VPD (Vapor Pressure Deficit – the difference in water vapour pressure) is an important factor for indoor growers. It is closely linked to temperature and relative humidity, affects plant transpiration processes and their ability to take up water and nutrients. Proper climate and VPD control are essential for healthy growth and development at every stage of a plant’s life. In today’s article, you will learn why it is important to monitor VPD indoors.

Even small changes in climate can have far-reaching consequences for plant development in indoor growing, and VPD is a good example of this. Maintaining the correct VPD values requires proper regulation of temperature and humidity, as well as adapting the climate in the growing space to the age and type of plants. In the following lines, we will look at how VPD works, why it is important to monitor it, and how to achieve ideal conditions at every stage of plant development.

What is VPD

VPD is closely related to the data we commonly monitor when growing plants indoors, specifically temperature and relative humidity (RH) in the growing space. Air temperature affects its ability to retain water in the form of vapour. Warmer air can hold more water than colder air. Relative humidity then indicates how much of the maximum possible water vapour capacity the air is currently holding. VPD expresses the difference between the amount of water vapour currently in the air and the amount it could hold at full saturation (i.e. at 100% relative humidity).

VPD is an important concept for understanding how the surrounding air affects plant transpiration processes. The unit of VPD is pressure expressed in kilopascals (kPa). The lower the VPD value, the more saturated the air is with water, which limits the plant’s ability to evaporate water and slows the rate of transpiration. This leads to lower water and nutrient uptake and creates a humid environment where mould, bacteria and other pathogens can easily spread. On the other hand, a high VPD value means that the air in the growing space is very dry and can hold more water. In such an environment, transpiration speeds up and the roots take up more water and nutrients. However, excessively rapid transpiration forces plants to close their stomata, which are pores on the leaves that serve for gas exchange (primarily CO₂ and O). with the surrounding environment. Excessively high VPD can lead to overfeeding and problems with water uptake.

VPD control

The exact VPD range may vary slightly depending on the species being grown; however, the decisive factor is primarily the age of the plants. In general, the younger the plants, the lower the VPD that is suitable for their optimal development.

• Optimal VPD range for seedlings and clones – 0.45 - 0.8 kPa - Clones, seedlings and young plants do not have enough leaves for rapid transpiration and require a humid environment. During the first weeks of a plant’s life, keep VPD at the lower end of the range.

• Optimal VPD for vegetative growth 0.75 – 1.25 kPa - During the vegetative growth period, plants have enough leaves to transpire large amounts of water and thus also take up larger amounts of nutrients. The aim is to increase VPD to the maximum without causing the stomata to close and reducing the supply of CO₂, which would slow growth.

• Optimal VPD for the flowering stage 1.2 – 1.5 kPa - During flowering and ripening, plants are sufficiently robust and able to transpire large amounts of water; however, flowers and fruits are sensitive to a humid environment. During the flowering stage, increase VPD to prevent water condensation.
• 

If you want to know the exact VPD values for a specific temperature and RH, look for online VPD calculators (VPD Calculator).

Steps for controlling VPD

Given how the VPD value relates to the current temperature and humidity in the growing space, the key to correct values is controlling these two variables. For example, when the air temperature drops after the lights are switched off, relative humidity usually increases and VPD decreases, which limits the rate of transpiration. In practice, this also means that more water condenses in the growing space. If you want to maintain the current VPD in such a situation, it is necessary to increase the air temperature in the grow room. Essential tools for controlling VPD are greenhouse heaters, dehumidifiers or humidifiers, and additional extract fans.

1. Measuring temperature and humidity: Place a sufficient number of thermometers with hygrometers in the growing space. Make sure you measure the readings not only at the tops, but also in the lower parts of the plants.
2. Temperature control: If the temperature in the growing space rises too high, increase the output of the extract fans, or consider installing air conditioning. In cooler conditions, you can use greenhouse heaters. Use a sufficient number of circulation fans to prevent cold or hot air from building up.
3. Humidity regulation: If the relative humidity in the growing space is too low, use humidifiers. They are especially suitable in the summer months and at the beginning of the growing cycle. Excessively high humidity can be solved with a dehumidifier, which is particularly important after the lights are switched off or during flowering, when there is a greater risk of mould.
4. Automating climate control: Climate control units (grow room controllers) automatically adjust temperature, humidity, ventilation and lighting based on the set parameters. Some modern devices can also calculate and monitor VPD.

Are you looking for complete guides on indoor and outdoor growing or the latest gadgets for growers? Do not hesitate to visit the Higarden blog!

Precise climate control is the foundation of success in indoor growing. Yet the correct placement of fans is often an overlooked detail that can significantly affect the microclimate in the growing space. Air circulation influences plant growth as well as their resistance to diseases and pests. In this guide, we will look at the importance of fans, their effective placement, and add tips for grow boxes and grow rooms.

When growing plants indoors, we use two basic types of fans, each for different purposes. Extract fans remove “stale” air from the growing space. Fresh air can be supplied passively, or a second fan can be used for this purpose, which is especially useful in larger grow rooms. Constant air exchange helps maintain a stable temperature and humidity in the growing space. A consistently optimal climate is important both for plant photosynthesis and as prevention against mould and the spread of pests.

Circulation fans placed inside the growing space are designed to imitate the natural wind that affects plants outdoors and stimulates them to form strong stems. Constant air movement also makes life more difficult for pests and discourages them from settling on plants. Correctly positioned circulation fans help prevent pockets of hot or cold air from forming, for example under lights or in the corners of the grow room.

Types of fans for indoor growing

• Clip-on circulation fans are the most commonly used type. They can be easily attached to the tent poles and are best suited to small or medium-sized grow boxes.
• Oscillating pedestal fans are suitable for moving air in medium-sized or large tents and grow rooms. They take up slightly more space than the clip-on version. They are usually larger and, thanks to oscillation, cover more of the growing area.
• Floor fans stand out for their high output and are most often used in large grow rooms, where they move air between the aisles with plants. They can also be used in large tents. Be careful with the strong air stream, which may damage plants.
• Extract fans of various types are an essential part of every indoor grow room. Older types with an AC motor are noisier and consume more energy than newer models driven by an EC motor. More modern versions of extract fans are easier to regulate and the purchase price is slightly higher.

Fan placement in small tents

In small grow tents with roughly up to 2 m² of growing area, you will usually manage with one extract fan and one circulation fan.

• Circulation fans should be placed in the corner of the tent 20-50 cm above the tops of the plants. The air stream should reach both the upper and middle parts of the plants. In a small space, the fan may be very close to the leaves, so set it to a lower output so that the air does not dry out the plants. For this purpose, small clip-on fans with or without oscillation are sufficient.
• Additional circulation fans are usually not needed in small grow tents. If you wish, you can place one small fan at the base of the tent so that the air is directed at the lower parts of the plants. In that case, the substrate will dry out slightly faster. Small clip-on fans are suitable for this purpose in small tents.
• Extract fan always belongs in the upper part of the tent so that it can efficiently remove warm air rising from the lights. An intake fan is not necessary in smaller tents.

Fan placement in medium-sized tents

Medium-sized grow tents with an area above 2 m² may require several circulation fans and one or two fans for extraction and possibly also air intake.

• Circulation fans should be installed in a similar way as in smaller tents, that is, in the corner 20-50 cm above the tops of the plants. If you want to ensure better air movement or are growing in a medium-sized tent, place a second circulation fan in the opposite corner. The air stream should be directed slightly above the tops of the plants towards the lights.
• Additional circulation fans can be used to move air near the floor of the tent or in the middle parts of the plants. This is especially useful if you are growing many plants close together, for example with the SoG method. For this purpose, you can use oscillating, floor or clip-on fans.
• Extract fans, just like in smaller tents, should be installed in the upper part of the grow box. In medium-sized tents, a second fan for air intake may also be needed.

Fan placement in large tents and grow rooms

Large grow boxes and grow rooms with tens of square metres of area require a more sophisticated ventilation arrangement to ensure sufficient air flow in all parts of the growing space.

• Circulation fans should be installed in every corner of the tent or grow room. Make sure the fans evenly cover the upper, middle and lower parts of the plants. For larger growing spaces, oscillating pedestal and floor fans are most suitable.
• Extract fans must have sufficient output in the case of large tents or grow rooms, and several units for air intake and extraction may also be needed. For successful climate control and optimisation in large spaces, growers usually use automatic climate control units.

Are you interested in the hottest tips for indoor growers and growers? Read the latest articles on our blog.

Tips for indoor growers are an inseparable part of our blog. This time we will focus on fresh air and its movement inside the growing space, where everything must be done to prevent the climate from getting out of control. So what kind of air are your plants breathing? To a large extent, that is also how well they do. And perhaps it is time to get things moving at last! Read on to find out how to ensure that the air in the grow box circulates properly.

It is rather surprising that regular air exchange or proper air circulation is among the most underestimated aspects of indoor plant cultivation, despite the availability of information today. The clear aim of this article is therefore to explain and remind readers of the importance of these aspects. Plants growing freely in nature automatically have a constant supply of fresh air with enough oxygen and carbon dioxide, which flows freely through the vegetation, thereby also ensuring the removal of accumulated moisture.

Nature, of course, has it all under control. Why, however, so many growers still take these processes lightly is still something of a mystery in the world of indoor gardening. If we use a closed greenhouse or have at our disposal a grow tent, or even an entire room for indoor plant cultivation, we have no choice but to account for completely different conditions than those outdoors and to try to imitate nature using proven methods.

According to experienced growers, we should not be lulled into a false sense of security by the fact that the plants look fairly healthy at first glance and are growing reasonably well. Such an approach could cost you tens of per cent of your potential yields unnecessarily! It would certainly be a shame to miss out on higher yields, which is why we will divide the following advice, related to the perfect climate inside the growing space, into two parts:

1. Air exchange
2. Air circulation

You probably already know that plants capable of photosynthesis consume carbon dioxide (CO2), while at night it is mainly oxygen. Humidity inside a closed growing space increases as a result of their transpiration. Given that a closed growing environment, for example a medium-sized grow tent, requires an intensive source of artificial lighting, replacing sunlight for the plants present there (partly in the case of discharge lamps or completely in the case of full-spectrum lighting), but also emitting a considerable amount of heat into the surroundings together with the light, which tends to accumulate inside the grow tent or room. Rising temperature and humidity in a closed environment... You have probably quickly imagined, from these words, what scenario would occur inside the grow box without sufficient ventilation. The transpiration activity of the plants would gradually cease. They would therefore be unable to cool themselves naturally, which would lead to their death.

Our TIP: The new Resin+ LED AX 600W 2.8 µmol/J also belongs among full-spectrum LED grow lights, simulating natural sunlight for plants, while emitting less heat into the growing space than a classic discharge lamp.

1. Air exchange

In terms of air exchange in the growing space, it is first necessary to distinguish between two types of environment, namely open or closed.

• If we mean a closed indoor growing room in the true sense of the word, we count on automatically controlled ventilation and CO2 supplementation (see separate article: Growing plants and carbon dioxide. How and why should it be used?). In practice, however, this usually concerns professionally equipped growing spaces for commercial growers.
• At the moment, we are more interested in home growing, and in this case we refer to the system as open, where a reliable extract fan removes air from the grow tent or room and fresh air flows into the growing space. These are the two options for achieving this effectively in the comfort of your home:
• Active air intake - this requires two fans. The one with the higher output serves to extract air (the so-called extract fan). As you will no doubt correctly suspect, the second fan in this setup serves to bring in air, and it is usually sufficient for it to have a lower output than the extract fan. Negative pressure controllers allow simple control of both fans at the same time and optimisation of their output.
• Passive air intake - fresh air is brought into the growing space thanks to the negative pressure created by the extract fan. If you opt for passive air intake, do not forget that the area of the intake opening for passive intake should be at least twice as large as the area of the extract ducting! Only then will negative pressure not prevail inside the grow box or indoor growing room, which would mean an insufficient supply of fresh air to the plants.

Our TIP: WHISPERBLOWER: professional fans with unrivalled efficiency (in the picture)

One of the most common questions from growers starting out indoors is which factors are most important when choosing air handling equipment for a grow box. Therefore, always consider the following first:

• What is the total volume of the growing space you will be using?
• What is the (average) air temperature and humidity of the air that will be brought into the growing space?
• What grow lighting will you use inside the grow tent or room?
• How many plants do you plan to grow inside the growing space? To what extent will it be filled?
• There is one more very important factor, without which this overview would not be complete, and that is duct resistance.

Returning to the first bullet point, it should be noted that the total volume of air in the growing space should be exchanged at least every 5 minutes and ideally every minute! There is never any shortage of examples, so for illustration let us imagine a grow tent with a volume of 2 m2. Although it might seem that a fan with a flow rate of 120 m3/h will be just right in this case, an experienced indoor grower will choose a fan that allows at least double the airflow, because they also take into account duct resistance (see the last point) and the odour filter. They will leave an even greater reserve if the pipes are long or bent. Simply put, the longer and more complex your ducting system is, the harder the fan has to work to extract air, and therefore it should have adequate output. It is always better to have a higher output available, which can also be easily reduced using controllers, than to have to buy a completely new, more powerful fan because you need more power.

Our TIP: Do you not want to design your growing air handling system yourself? Use a complete tailor-made indoor solution in the form of our cost- effective grow box sets, assembled by our experts (example in the picture). You can leave the technical concerns to us and simply connect the whole system at home and start indoor growing.

2. Air circulation

One thing is to ensure that plants grown in a closed environment breathe nothing but fresh air through their leaves. However, many growers forget that air exchange and air circulation are interconnected.

It is therefore also necessary to think about proper air circulation, which is absolutely crucial in a closed space of several cubic metres if we want to maximise the genetic potential of the plants being grown.

But beware! Everything in moderation. If you overdo the airflow provided by circulation fans, you will expose your plants to unwanted stress and may even damage their leaves. For this reason, it is important to place a circulation fan inside the grow tent or room so that the air always blows level with the tops of the plants. Truly even air circulation and the associated homogeneous climate in the growing space will be ensured by installing a larger number of circulation fans, about which you can learn everything you need in a separate article: How do you choose a circulation fan?

And these are the three reasons why we do not know anyone who does not use circulation fans in a grow tent:

• Photosynthesising plants consume carbon dioxide. They exhale oxygen and moisture. In the immediate vicinity of the leaves, a climate gradually accumulates that is so-called stale and no longer allows the leaves to function normally.
• Fresh air that has just been brought into the growing space is effectively mixed by circulation fans, thanks to which no areas with different temperatures arise in the grow tent or room and overheating of plant leaves is also prevented.
• What is second nature outdoors is once again provided indoors by a circulation fan, whose operation gently moves the plant stems through the airflow, forcing them to strengthen healthily. The leaves of the plants should be in slight motion at all times. This also clearly shows you whether the air in the growing space is circulating continuously. This is easiest to check with grow tents whose construction has viewing windows, such as the BudBox PRO XL (see separate article: BudBox - stable grow tents are number one in England).

After reading the above lines, you should have no doubt whatsoever that a constant and at the same time sufficient supply of fresh air to all leaves in a closed growing system is a basic prerequisite for effective photosynthesis, and thus for high yields indoors.

Would you like to ask us something? We are here for you at the well-known e-mail address info@higarden.eu. We will be happy to advise you, for example, on choosing the right air handling equipment.

We also recommend these products:

• LED Set 720W Lumii Black
• Clip fan PF 15 cm 15W 2 speeds
• VDL TT 100 fan, 145/187 m3/h

What to read next

• Prima Klima - fans for maximum output and minimum noise
• VIPARSPECTRA and growing under LED - definitely a good idea!
• Do you know what VPD is? Discover the key to perfect conditions for plant development

Although summer is now irretrievably behind us, the heating season is already in full swing. That is why the topic of high temperatures remains highly relevant, as they can quite easily become the cause of restricted growth or flowering in your precious plants and, in the worst case, even permanently damage them. In this article, you will learn how and why to deal with high temperatures inside a grow tent or room. And it will not be only about air temperature. Among other things, we will also remind you why substrate temperature is important. You will also learn the difference between temperatures that suit the roots and the above-ground parts of plants.

Are you wondering why plants every year tolerate extreme temperatures so poorly, not only outdoors during summer, but also in overheated rooms during the winter months? It is because if the environment in which they grow is too hot, the plants can no longer cool themselves sufficiently through the process called transpiration. Simply put, they cannot keep up with releasing water, and the hot air causes them to dry out relentlessly and gradually deteriorate. This is, of course, a problem that needs to be prevented or at least addressed in time. It is also worth noting that plants grown outdoors are partly adapted to summer heat, because they cannot escape it in nature. As an indoor grower, however, you can take the right steps so that your harvest never again suffers from high temperatures and hot air.

What can high temperatures in the tent cause?

Otherwise, nutritional deficiencies will sooner or later appear (see separate article: Symptoms of a deficiency of important nutrients), or the signs of their undesirable excess. In addition, plant growth usually slows down significantly, and the leaves may also die off. If the leaves do not die directly in such cases, they usually curl and dry out. Once your plants start to wilt, things are really serious. That is almost the end, when irreversible degenerative processes occur and the harvest is permanently devalued.

Dealing with high temperatures in indoor growing

Now let us focus on the most important factors related to temperatures in the growing space within indoor plant cultivation, which you can influence as a grower.

• SOURCE OF ARTIFICIAL LIGHTING

You may already know that especially powerful discharge lamps emit a considerable amount of heat into their surroundings in addition to light radiation. Although many growers still swear by classic discharge lamps, whether out of habit or for other reasons, modern LED lamps are gradually, but surely, overtaking them on the grow lighting market.

Our TIP: LED Set 720W Lumii Black

LED grow lighting can work with electrical energy more efficiently, converting it into light radiation. Thanks to this, increasingly popular LEDs do not raise the temperature inside the grow tent nearly as much as discharge lamps do. You can read about other differences between discharge lamps and LED fixtures, such as the composition of the light spectrum or electricity use, in a separate article: Growing under artificial lighting: HPS vs. LED.

The good news is that you can at least partly control the heat generated inside the grow tent when using powerful discharge lamps. On the one hand, you can temporarily reduce the light output, because plants suffering from excessively high temperatures will not be able to make use of high PPF values anyway, but above all, when using a discharge lamp, you can take advantage of air-cooled reflectors or COOLTUBE-type reflectors.

• VENTILATION AND AMBIENT TEMPERATURE

 The temperature inside the growing space is, of course, primarily determined by the temperature of the surrounding air that is brought into it. Indoor growers are not some special species that likes freezing at home in winter, but in some cases it is still worth lowering the temperature in a comfortably heated room by at least a few degrees. In summer, there is nothing better than air conditioning, which is not among the cheapest equipment, but especially second-hand it can become a more accessible solution that will significantly make home growing of herbs, fruit or vegetables easier for you. Other proven tips include switching the grow lights on only at night, when temperatures are usually lower. And if the layout of your flat, or the placement of the grow box, allows it, bring fresh air into it directly from outside using an intake fan connected to ventilation ducting.

This brings us to the flow of fresh air around the plants, which is unnecessarily underestimated in indoor gardening, at least at hobby level and in the early stages. But remember that the more fresh air you “move” through the growing space, the better the plants grown inside are able to cope with higher temperatures. It is important that the air being extracted from the grow room does not mix with the fresh air that is still flowing into the growing space. It would affect both its temperature and humidity. The quality of a well-designed ventilation system is simply essential. On this topic, we also recommend the following separate articles:

• How to choose and assemble tent ventilation
• How powerful a fan do you need?

And how can you ensure that the hot air in the grow room does not stand still, but instead keeps flowing around the plants? Simple! That is exactly what circulation fans are for, as they are indispensable helpers for every indoor grower, and cheaper versions can be bought for literally a few pounds. You can learn everything important in a separate article: How to choose a circulation fan?

Our TIP: Clip fan PF 15 cm 15 W, 2 speeds

• HUMIDITY

When growing plants indoors in a grow box, it is not so much about the fact that the relative humidity inside the tent directly lowers the temperature, but it can certainly be said that higher humidity inside the growing space helps plants cool themselves more effectively. And that is exactly what we need when temperatures are too high at a given moment. Temperatures approaching 30 °C require at least 70% humidity in the environment. A high-quality and powerful ultrasonic air humidifier is a great helper in these cases, except in the late flowering stage. For your plants grown in the grow box to achieve the optimal level of transpiration, it is good to understand the relationship between temperature and humidity, which a separate article will help you with: Do you know what VPD is? Discover the key to perfect conditions for plant development.

• TYPE OF GROWING MEDIUM AND ROOT SYSTEM

Are you used to the classic combination of a pot and soil substrate, or do you prefer hydroponic systems, in which you use inert hydroponic media, or perhaps coconut substrates? It is also important to realise that the chosen growing medium and the selected irrigation method will affect the plants’ ability to take up water. The easiest time of all is in hydroponic or aeroponic systems.

High temperatures then pose a threat especially to growers who cultivate plants in soil, which is not as airy as coconut coir, for example. And the combination of high soil temperature that is also waterlogged, which is one of the most common beginner mistakes, opens the door wide to root rot. So if you are dealing with high temperatures inside an indoor grow room, you will achieve better results if you opt for airy growing media and self-watering systems. In such a case, however, you must keep an eye on the temperature of the nutrient solution. (We also recommend the separate article: Why and how to maintain a stable nutrient solution temperature?) The above-ground parts of plants are prepared for temperatures around 30 °C, but the temperature in the root zone should be about ten degrees lower and should not deviate too much from the optimal 21 °C. This is because plant roots need as much oxygen dissolved in the water as possible, and its content decreases as temperatures rise.

The previous lines therefore show that in a grow tent and in indoor gardening in general, it is not only about air temperature, but also about the temperature in the root zone, which is often unnecessarily overlooked. Most fast-growing plants are comfortable at temperatures in the range of 20 - 30 °C, but remember that for the roots, unlike the above-ground parts, the lower limit will always apply.

Our TIP: Time-tested prevention for plant health and resilience is Cannazym - a blend of more than 12 types of enzymes, enriched with vitamins, which intensively supports the breakdown of dead roots and their subsequent conversion into nutrients usable by the plant.

High temperatures should no longer hold you back when growing plants indoors. And if you want to ask us anything, we are here for you at the well-known e-mail address info@higarden.eu.

We also recommend these products:

• PrimaKlima Cooltube
• CO2 Generator MOTHER NATURE
• Red Scorpion METAL fan 100 mm, 320 m3/h

What to read next:

• VIPARSPECTRA and growing under LED - definitely a good idea!
• Comparison of top LED lights from Lumatek: ZEUS PRO vs. ZEUS PRO 2.9
• TechGrow again: microclimate under control thanks to flawless multifunction controllers!

Are you dealing with unwanted odours drifting indoors from your grow tent? It is the right time to install an odour filter with activated carbon into the ventilation system. Effective carbon filters from the leading manufacturer Prima Klima are used not only in indoor plant cultivation, but also in industrial premises or in the home. This article introduces their features so that you can more easily choose the right one across the product ranges.

Depending on requirements and needs, filters from the Prima Klima brand cater to all customer categories and offer the right carbon solution, whether you prefer affordability or the longest possible odour filter lifespan. Regardless of the product range, they have long been a guarantee of high quality and reliability for customers. The German manufacturer, which produces these popular, high-quality odour filters in the Czech town of Radnice, does not take the environmental aspect lightly either and has long paid attention to sustainability in production. That is why Prima Klima odour filters with activated carbon are almost 100% recyclable.

Highly porous activated carbon as the basis

This is also related to the use of activated carbons, which perfectly absorb odour particles. CTC-75 carbon is a product of human activity and easily solves the problem of unwanted odours in enclosed spaces. If we enlarge this activated carbon from coconut shells under a microscope a thousand times (image on the left), we find that its porosity is much greater than in the case of commonly used activated carbon (image on the right).

We now come to the individual product ranges. Which are they?

Prima Klima PITPUK

The Pit Puk range represents a specific modular filtration system, characterised by excellent adsorption of odour particles using pellets of highly active virgin carbon. Adsorption is a process in which gaseous, liquid or solid particles (odour particles) accumulate on the surface (carbon layer). This type of carbon filter can be used for both intake and extract air. Depending on airflow, humidity level and the presence of organic compounds, expect an average service life of two years.

The unique odour-removal filtration system consists of the following parts:

• PIT: plastic flange - an impact-resistant part made of high-quality, durable nylon (polyamide). This material is also non-flammable and completely odourless.
• PUK: carbon filter cartridge - the activated carbon cartridges are easy to replace and can also be conveniently stored as needed.

How to assemble the Pit Puk filtration system is shown in the manufacturer's video. We recommend buying the complete PITPUK filtration system straight away: Prima Klima PITPUK Starter Kit 125 mm. In the image you can see what it looks like when connected to the extra powerful PK125ECblue fan.

Prima Klima Eco Line

The ECO Line filters provide reliable odour removal and are characterised by an excellent price-performance ratio, which is also the main reason why they have long been among the most popular on the market. They are the ideal choice if you do not know which odour filter to choose, as ECO Line filters are simply a timeless classic, with a whole range of variants to choose from. (At the end of this article, we will guide you so that you know what to look for when choosing a specific filter.)

To ensure an optimal level of air filtration, each filter in the ECO range has a 3 cm layer of highly active carbon with an area of >1200 m²/g and the same quality as in the professional Industry LINE filters.

Given the price, it is then a pleasant surprise that even the “economy” variants in this range are equipped with a pre-filter against dust.

Filters from the Prima Klima Eco range cannot be refurbished. Their service life is usually around 9 months. In some cases, it reaches one year. As with any filter, the above factors (airflow and humidity of the filtered air, impurities, etc.) can again affect it.

Prima Klima Industry Line

The premium INDUSTRY range includes professional carbon filters with a pre-filter against dust, which will satisfy even the needs of demanding customers. The refillable filters are characterised by a 4 cm thick bed of highly active CTC75 carbon with an area of >1200 m²/g, as well as a robust and stable steel construction. What can you expect if you pay extra for them?

• Extra long contact time between air and the activated carbons. It is simple: longer contact allows better air purification. The result is an exceptional level of odour absorption.
• The above-standard service life of these filters is usually in the range of 1.5–2 years, again depending on the factors mentioned above.

Prima Klima CARBOCONE

Finally, we have high-tech odour filters with a patented conical inner basket design, whose uniqueness is best illustrated by the manufacturer's video or our separate article: Prima Klima CARBOCONE: innovative activated carbon filters. In short, it is their unique structure, thanks to which they can boast the longest service life on the market. While the carbon layer of ordinary odour filters gradually fills with odour particles unevenly over time, the structure of Carbocone filters guarantees even saturation of the carbon. This brings the following benefits for users:

• Lower consumption of activated carbon
• The longest service life on the market (+ 30%) 
• Significantly more efficient absorption

Our TIP: Do not forget that the specific odour filter model should be chosen mainly according to the flange size or airflow. So if you are choosing your first activated carbon filter, be sure to read what to watch out for when selecting a carbon filter. For this purpose, we have prepared a separate article for you: Odour Filter – How to Choose?

We will also be happy to advise you on anything you are interested in, for example at the well-known e-mail address info@higarden.eu.

We also recommend these products:

• Activated carbon
• Replacement Pre-Filters Prima Klima
• PRIMA KLIMA fan 400 m3/h, 125 mm, with thermal control (PK125-TC)

What to read next?

• WHISPERBLOWER: professional fans with unbeatable efficiency
• VIPARSPECTRA and growing under LED - definitely a good idea!
• How to choose and assemble tent ventilation

VPD (vapour pressure deficit = the difference in water par) is still a big unknown for many growers. On the other hand, more and more home growers have recently been getting acquainted with the topic of VPD, especially those who devote themselves to indoor gardening in their grow box. Join them thanks to the information you will absorb in this article. For professionals, knowledge of VPD and its use in growing practice is then a matter of course. Join them and reach a new level!

All growers certainly want to provide their plants with perfect conditions for development. To give them an ideal climate inside the growing space so that they can later enjoy a wonderful, flawless, abundant harvest. However, when it comes to the climate inside a grow tent or indoor grow room, most growers deal only with factors such as temperature or humidity. These factors can be directly influenced using common equipment, whether it is quality ventilation equipment or suitably chosen artificial lighting for plants. Even measuring temperature and humidity is no science at all.

VPD and the importance of plant transpiration

Transpiration is the process by which plants breathe and release water through stomata, which are pores on the leaves. Intensive transpiration of plants through the stomata on the leaves is extremely important for plants, because the amount of water a plant exhales is always closely related to how much water with nutrients (feed solution) it is able to take up through its root system. 

Now comes an important fact. The rate of plant transpiration largely depends on the difference between the water vapour pressure in their stomata and the water vapour pressure in the surrounding air. This also explains the concept of VPD without unnecessarily technical wording. The difference in water vapour pressure simply tells us how strong the “drying” power of the air around the plants is, which directly affects the intensity and overall quality of their transpiration.

The water vapour pressure around plants always depends on the temperature and humidity of the air in the growing space. The humidity inside the stomata on plant leaves can generally be considered 100%. The pressure is influenced mainly by leaf temperature. If we measure leaf temperature in addition to air temperature and humidity, we are able to calculate the difference in water vapour pressure between the stomata and the surroundings of the leaves from the measured values. In relation to the current stage of the plant’s life, we can therefore maintain and control VPD. And that is great news, because if you can keep VPD under control throughout the growing cycle, your plants will thrive much more!

How to achieve the correct VPD?

You may be wondering what the catch is. The best thing about it is that there is practically none. It is enough to measure responsibly the main factors affecting the difference in water vapour pressure. Repetition is the mother of wisdom and, in this case, of high yields too, so for completeness we provide a clear summary of them:

• air temperature
• leaf temperature
• relative humidity of the air
• light intensity
• substrate moisture and EC substrate

Our TIP: Get the practical and elegant Milwaukee KIT case with waterproof instruments for reliable, regular measurement of pH and EC.

Accurate measurement and influencing of the individual factors affecting VPD is truly essential if you want to use this knowledge for a better harvest. On the internet you will also find many tables with generally recommended values for the difference in water vapour pressure. To begin with, remember a simple but most important rule: The leaf surface must always have a lower temperature than the surrounding air! If it were the other way round, the rate of plant transpiration would not be sufficient, the plants would not cool down enough and, in the end, they could suffer irreversible damage or, in the worst case, die.

This description of the opposite and undesirable state again clearly shows how important the difference in water vapour pressure is when growing indoor. At a certain point, most growers (especially in the beginning) encounter seemingly inexplicable problems. At first glance, the plants do not look vigorous, show signs of nutrient deficiencies and their leaves are wilting. In this situation, growers ask themselves and more experienced colleagues where the problem is, and they search in vain for the reason why they still cannot achieve satisfactory results. After all, they apply fertilisers exactly according to the manufacturer’s dosage tables and give their plants almost more care than they give themselves!

Practical examples

• If the difference in water vapour pressure is too high, the plants cannot cool down sufficiently because the surrounding air dries them out too quickly. As a result, the plants do not develop as they should. They usually also show symptoms of nutrient deficiencies, which we covered in a separate article: Symptoms of a lack of important nutrients. In these situations, the leaves of the plants often dry out, curl up or gradually die off.
• How does this happen? In indoor gardening, the most common cause is a combination of low air humidity and a powerful discharge lamp.
• Now the opposite scenario. A too low difference in water vapour pressure prevents plants from transpiring, the importance of which you already know from the previous lines. It is therefore no surprise that, as a result of too low VPD, the surrounding air is no longer able to absorb additional moisture and transpiration cannot take place. A clear indicator of this scenario is moisture condensed on the leaves of the plants and their slow growth. Again, signs of deficiencies in important nutrients can be observed and an ideal environment is created for the development of fungal diseases in plants.
• How does this happen? A classic example from the world of indoor plant growing is the combination of low temperatures and LED lighting, whose diodes heat the surrounding air in the growing space much less than discharge lamps.

Would you like to ask us something? We are here for you, whether by phone or at the well-known e-mail address info@higarden.eu. We look forward to your questions!

We also recommend these products:

• HUMIPRO 4L ultrasonic humidifier
• Garden Highpro Clip Fan 15CM / 15W, 2 speeds
• PRIMA KLIMA EC WHISPERBLOWER fan

What to read next:

• Symptoms of a lack of important nutrients
• Discover modern Garden Highpro grow boxes
• CANNA substrates and fertilisers: 30 years of research for successful plant growing indoor and outdoor

For many growers, the main advantage of indoor cultivation is the discretion that this method of plant cultivation offers. However, a grow room or grow tent can easily give itself away through compromising odours that may be bothersome or attract unwanted attention from the surroundings. In the following article, we will focus on methods that will help you effectively neutralise odour from a grow room or grow box.

Odour filters with activated carbon

Carbon filters that absorb odours are now part of the basic equipment of every grow room or grow tent. They work on a simple principle, where air from the extract fan passes through a cylinder filled with activated carbon, which captures the particles causing the odour.

• Appropriate size: For a carbon filter to work properly, its size and capacity must match the output of the extract fan. For example, for the PRIMA KLIMA extract fan with an output of 400 m3/h, a PRIMA KLIMA odour filter with a capacity of 480 m3/h is suitable. The maximum permitted airflow should always be higher than the fan output so that clogging of the ventilation system does not occur as the filter wears.
• Installation: Most growers connect the odour filter before the extract fan so that all air from the growing space comes into contact with the activated carbon. Air without odour then exits the ventilation duct outside the grow box or grow room. If the layout of your growing space does not allow this setup, you can also connect the filter at the end of the ventilation system in the direction of airflow. However, this method may not be as effective due to possible leaks in the ducting or tent. When installing an odour filter, you will need cable ties and ventilation ducting to connect the individual components.
• Regular maintenance and replacement: Activated carbon filters are extremely effective, but they do not last forever. Roughly every 6-10 months or every three growing cycles, replace the worn odour filter with a new one. You can extend the service life of the carbon filter by cleaning or replacing the white protective fabric after each cycle, as it traps dust and solid particles.

Do you not want to worry about assembling a ventilation system for your grow box? We have prepared ventilation kits for you, which include an extract fan with a custom odour filter and all the accessories needed for installation.

Gels and sprays for odour neutralisation

Chemical products for odour neutralisation contain aromatic substances that release an intense fragrance while also absorbing other odours. Thanks to their easy handling, the main advantage of odour absorbers is their universal application. Another benefit is their immediate effect, which you will appreciate, for example, during harvest.

• Use: To avoid affecting the terpene profile of the plants, we recommend placing chemical odour absorbers outside the growing area.
• Installation in ventilation ducting: For maximum effect, we recommend connecting a duct connector with space for placing an odour neutraliser in gel or a similar form into the ventilation system.
• Automatic dispensers: We recommend placing the ONA Block Dispenser and other automatic dispensers near the entrance doors to the grow room or room with the grow box.

Further tips for odour control

In addition to using carbon filters and chemical odour neutralisers, you can take several simple measures that will further reduce unwanted odours in your grow room or grow box.

• Adequate ventilation: Make sure that your growing space is sufficiently ventilated. It is important not only to have a sufficiently powerful extract fan, but also access to fresh air.
• Seal all gaps: Leaks in the grow box or in the ventilation ducting are a common cause of unwanted odour. It is important that as much air as possible passes through the extract fan with the carbon filter.
• Air ionisers: High-performance air ionisers are suitable for large growing rooms for medicinal plants. These are generators of negative ions that absorb odours and remove dust particles from the air.

Would you like to learn more about indoor growing and the most modern gardening techniques? You can find all this and much more on our Higarden blog!

One of the main attractions of indoor growing is that you can cultivate all year round, regardless of the whims of the weather. However, it is not entirely true that indoor growers are unaffected by the changing seasons. Even a small drop in temperature in the growing area causes fluctuations in VPD and slows down plant metabolism. You can learn how to prevent this in the following article.

Most plants grown indoors grow best at temperatures in the range of 21-29 °C, with the difference between day and night temperatures not exceeding 5 °C. As soon as temperatures fall, plants slow down their metabolism and the rate of photosynthesis. This means that even if we provide them with a large amount of energy in the form of light, they will not be able to use it to produce sugars and will grow more slowly than they would at higher temperatures. If the temperature drops below 15 °C, plants stop growing and remain stunted.

Plants also respond to low temperatures by slowing transpiration, that is, the rate at which they evaporate excess water through their leaves. Transpiration is crucial for the transport of nutrients and water. A smaller volume of water evaporated through the leaves means that plants use less water, but at the same time they stop taking up nutrients from the substrate or nutrient solution. The result is again slower growth and also an increased risk of overwatering substrates and root rot.

Growing at lower temperatures can also bring some advantages, especially in the prevention of pests and mould. Cold air retains less moisture and is drier than warm air. This can be useful in preventing moulds such as powdery mildew or Botrytis cinerea, which causes flower rot. At low temperatures, some insect pests, such as spider mites or aphids, also reproduce more slowly. However, remember that if the temperature drops below 15 °C, plant metabolism stops completely and they cease to grow.

The effect of low temperatures on VPD

Plants are affected by the temperature and humidity of the air surrounding them. Air temperature affects transpiration and relative humidity plays a significant role in CO2 uptake, which is important in the process of photosynthesis. The effects of climatic conditions on plants are best expressed by vapour pressure deficit (VPD). We covered this topic in detail in an older article on our blog. VPD values are derived from the temperature and relative humidity of the air in the growing area, and even small fluctuations in temperature (+-1 °C) or humidity (+-5 % RH) can represent significant changes in vapour pressure deficit. If you use VPD as a guide when growing plants indoors, it is extremely important to maintain a consistently stable and optimal temperature and humidity in the growing area.

How to keep the grow box sufficiently warm

During winter, you have several options for increasing the temperature in the grow box. The simplest and cheapest solutions consist of insulation, or alternatively blowing in warm air or moving the grow tent to another location. Slightly more expensive (but more reliable) is heating the growing space with a heater or replacing the grow lighting.

Insulate the grow box: Before you start heating the growing area, make sure that the grow box seals properly and check all zips so that warm air does not escape. If pots or the irrigation system stand on a cold floor, place them on a suitable insulating material, such as polystyrene.

Use warm air from another part of the house: During the winter months, it may be advantageous to bring warm air from heated rooms into the growing area. It is also a good idea to place the grow tent closer to heat sources, for example next to a radiator.

Heaters for the grow box: If insulation and the supply of warm air are not enough, consider getting a suitable heater. For grow boxes, tubular greenhouse heaters are particularly suitable, or hanging heaters. Most heaters are equipped with a thermostat, which keeps the temperature in the growing area stable. Heating the room in which the grow tent stands can also be a solution. Oil-filled or electric radiators are suitable.

Switch to another type of grow lighting: Modern LED grow lights stand out for their efficiency and therefore do not emit too much heat into the surroundings. Older grow lights using sodium discharge lamps (HPS) emit a considerable amount of heat, which can be an advantage in the winter months.

Whether you decide on insulation, moving the grow box, or investing in heating and new lighting, always keep in mind that a stable temperature is the key to success. For more tips and tricks on how to grow even in the winter months, visit our Higarden blog.

How do you choose the right ventilation ducting for your indoor grow room or grow box? We have prepared an overview of three basic types of ventilation ducting and practical tips for their use.

Choosing the right ventilation ducting is essential for the efficient operation of the ventilation system in your indoor grow room or grow box. Ventilation ensures air circulation, removal of excess moisture, temperature regulation and odour removal, all of which are key factors for the healthy growth of your plants. In this article, we will introduce three basic types of ventilation ducting, their advantages and disadvantages, and provide practical tips for their correct use.

ALU aluminium ducting (ALUFLEX)

Flexible ALU ducting is made from a combination of aluminium and laminate. The ducting structure consists of steel wire wound between several layers of material, which gives it the necessary flexibility. ALU ducting is easy to shape, which allows simple attachment even in hard-to-reach places or where obstacles need to be avoided. The ducting material withstands temperatures from -30 °C to 140 °C and a maximum pressure of 2,500 Pa at an air speed of up to 20 m/s. ALU ducting is particularly suitable for connecting fans and carbon filters.

Rubber-coated COMBI ducting (COMBIFLEX)

Flexible COMBI ducting is designed to be resistant to mechanical damage. The inner part is made of aluminium, while the outer layer consists of a durable protective plastic. COMBI ducting is durable and flexible at the same time, so it can be used for complicated and heavily loaded connections. The COMBIFLEX material can handle temperatures from -30 °C to 140 °C and a maximum pressure of 3,000 Pa at an air speed of up to 30 m/s. COMBI ducting is suitable for air distribution as well as connections between fans and odour filters.

Acoustic SONO ducting (SONOFLEX)

Flexible SONO ducting minimises noise caused by flowing air. The ducting consists of a hardened aluminium inner section wrapped in an insulating layer of mineral wool. SONO ducting significantly reduces the noise level of the ventilation system and is particularly suitable for air distribution. Like the other types of ducting, SONOFLEX withstands temperatures from -30 °C to 140 °C and a maximum pressure of 2,000 Pa.

Tips for installing ventilation ducting

When installing ventilation ducting, bear in mind that every obstacle the air hits reduces the efficiency of the fans and increases noise. The fewer bends and the shorter the duct runs, the quieter and smoother the operation of the ventilation system will be. Use metal cable ties to attach the ducting to fans, odour filters and connectors, and check the joints from time to time to make sure they are sufficiently sealed. Between individual growing cycles, dismantle the ventilation system, clean it and, if necessary, replace worn parts.

You may also be interested in: Where and how to position fans in a tent or grow room

Are you starting with indoor growing and looking for beginner tips and advice? Visit our Higarden blog, where you will learn everything you need to know about indoor growing under artificial lighting, hydroponics and urban growing.

Although Central Europe is no Sahara, many indoor growers are forced to switch off their grow room during the hot summer months. Plants grown indoors thrive best at room temperatures, and although they can withstand more extreme heat for a short time, this has a significant impact on their health and yield. In the end, it may not even be worth switching on the equipment. But how should you set up your grow room so that you can cultivate all year round?

Replace outdated discharge lamps with LED lighting

If you are still using discharge lamps (HPS, MH), summer is the ideal time to switch to LED grow lights. Discharge lamps emit a lot of heat and convert up to 70% of the energy they consume into infrared radiation, which directly heats the growing space and does nothing to support plant growth. LED luminaires have lower power consumption and produce minimal heat, which will significantly reduce the temperature in the growing space. In addition, you will save on electricity bills, because compared with discharge lamps, LED diodes convert much more of the supplied energy into photosynthetically effective radiation in the PAR spectrum.

Pro tip: If you light during the day and are struggling with high temperatures inside the growing space, try lighting your plants at night, when it is cooler.

Improve ventilation and air circulation in the growing space

It is obvious that the better and faster you manage to remove heated air from the growing space, the cooler it will be inside. Before you start buying new equipment, however, first check what you already have. A common cause of ventilation problems is clogged carbon filters and fans, or leaking ducting and joints. If that does not help, try the following:

• Increase extract performance: Check whether your fan can handle the increased load. It may be time for a more powerful model.
• Maintain negative pressure in the grow box: Ideally, the extract performance should create slight negative pressure in the grow tent. You can tell this by the “sucked in” walls of the grow box.
• Add circulation fans: Circulation fans not only help plants develop strong stems, but also prevent hot air from building up in one place.

You may also be interested in: Where and how to position fans correctly in the grow room

Air conditioning and cooling

If you have tried all of the above advice and still need to reduce the temperature in the grow box a little, it is time to use air conditioning. Air conditioning units are relatively expensive to run, so use them efficiently. Always vent the warm air from the air conditioning unit outside or into another room. Use timers and thermostats so that the air conditioning runs only when it is absolutely necessary.

CO₂ supplementation

Although for most growers the best approach is to keep the temperatures in the grow box at optimal levels, under certain circumstances they can be an advantage. Specifically, this refers to supplementing the atmosphere in the growing space with carbon dioxide. Plants use CO₂ during photosynthesis, during which they absorb light and convert it into energy in the form of glucose. Higher concentrations of carbon dioxide allow plants to carry out photosynthesis at higher temperatures. Under normal conditions, the air contains around 400 ppm of CO₂, which allows plants to carry out photosynthesis efficiently at temperatures between 25 and 30 °C. It has been found that if the CO₂ content is increased to 1935, this temperature can rise to as much as 36 °C.

Interested in the latest news from the growing industry and practical advice for growers? Visit our Higarden blog.