Fertilisers: A Complete Guide to Buying Plant Nutrition for Your Plants

Fertilisers: A complete guide to choosing plant nutrition

You’ll find dozens of brands and hundreds of different types of fertilisers on the market – in liquid, powder and solid form, organic and mineral, for different growth stages and growing methods. How do you make sense of it all and avoid choosing the wrong one? We’ve put together an overview of the main types of fertilisers, along with practical advice to help you choose the right nutrition for your plants.

Main types of fertilisers by growing medium

Fertilisers for growing in soil, coco, inert growing media or hydroponics are different. Before you start shopping for fertiliser, decide what growing medium you’ll use and how you want to grow your plants. You can then choose the right type of nutrition.

• Fertilisers for soil: Suitable for growing in open ground (in beds) or in pots.
• Fertilisers for coco growing media: Growing media made from coconut fibres do not contain nutrients themselves and require special fertilising. Coco growing media are generally used for indoor growing or in greenhouses.
• Fertilisers for hydroponics: Intended for preparing nutrient solution for soilless systems or for growing in inert media such as rockwool.

You may also be interested in: A guide to growing media

Choosing fertiliser by growth stage

From germination to harvest, plants go through several growth stages, and their nutrient requirements change accordingly. During the first few weeks of their lives, they need little or no fertilising. During the vegetative growth stage, it is important to provide them with enough nitrogen, while during flowering it is a good idea to use fertilisers with higher potassium and phosphorus content.

• Starter fertilisers-Start: Contain small amounts of nutrients and often also substances that support root growth and beneficial microorganisms, such as mycorrhizal fungi or soil bacteria.
• Fertilisers for the growth stage-Grow: Contain higher amounts of nitrogen, which plants need to produce leaves and stems. Nitrogen fertilisers can be purely organic, mineral or combined, and the nitrogen they contain may be in the form of nitrates (NO₃-) or ammonium (NH₄+), which affects how quickly it is absorbed and influences fluctuations in the pH of the growing medium.
• Flowering fertilisers-Bloom: Contain higher amounts of phosphorus and potassium to support flower and fruit production and, like other types of fertilisers, can be organic, mineral or combined.
• Fertilisers for the pre-harvest period-Flush: Particularly when growing medicinal plants, some growers stop using fertilisers several weeks before harvest and replace them with plain water or special flushing fertilisers or finishers. The aim is to improve the aroma and flavour of the harvested product.

You may also be interested in: What are NPK fertilisers and what are they used for?

Organic vs. mineral fertilisers

Although plants do not care where the nutrients absorbed by their roots come from, the difference between organic and mineral fertilisers is significant when growing plants. Organic fertilisers are effective only in the presence of soil microorganisms, so they are suitable only for growing in soil-based (organic) growing media or in beds. Synthetic fertilisers contain mineral salts, which plants can absorb directly from water and which can be used for growing in coco, inert growing media and hydroponic systems.

• Organic fertilisers: Made from natural materials such as compost, manure, bone meal, guano, fish, seaweed or plant extracts. When using organic fertilisers, bear in mind that it takes some time for them to start working.
• Mineral fertilisers: Contain nutrients in the form of mineral salts, which are obtained from phosphates and ammonia, or by synthesising nitrogen from the air. They work immediately, but there is a risk of over-fertilising. Therefore, always follow the dosage charts and measure the pH and EC of your watering.

You may also be interested in: Organic vs. synthetic fertilisers: Which is better for your plants?

Fertiliser form: liquid, solid or powder?

Fertilisers come in several forms – from liquids to loose powders and solids with slow-release properties. Each form has its advantages, depending on where and how you grow. Both organic and mineral or combined fertilisers are available in different forms.

• Liquid fertilisers: From a user’s point of view, concentrated fertiliser solutions for preparing watering are the most convenient. They work quickly, are easy to use and have a long shelf life.
• Dry fertilisers: Water-soluble fertilisers in powder or granule form can be used to prepare nutrient solution or applied directly to the growing medium (if designed for this purpose).
• Slow-release solid fertilisers: Fertilisers in the form of slow-release pellets or granules are suitable for outdoor growing because they leach out of the soil more slowly and supply nutrients to plants gradually. The drawback is that they are more difficult to dose.

You may also be interested in: Dry vs. liquid fertilisers: Which are better for growing?

Complete nutrition: Multi-part vs. single-part fertilisers

Multi-part fertilisers are commonly used, particularly for hydroponic growing. They are mixed in specific proportions to create the ideal nutrient solution for each situation (for example, with more nitrogen during the growth stage or more phosphorus and potassium during flowering). Single-part fertilisers, on the other hand, contain a set proportion of nutrients, usually for a specific growth stage (veg/flowering).

Nutritional supplements and stimulants

Alongside basic fertilisers, which contain the macro- and micronutrients essential for plant growth, growers can also find a range of nutritional supplements and growth stimulants in specialist shops. These additives are not usually essential for growing, but many growers use them to help their plants reach perfection.

• Root stimulators: Speed up root formation and are used during germination, propagation from cuttings or when transplanting plants.
• Growth and flowering boosters: Stimulate plants to produce leaves or flowers.
• Vitalisers and enzymes: Various types of additives that protect plants from stress and support microbial life.

You may also be interested in: When and how to use root stimulators

You should now be ready to buy the right fertilisers for your plants. Before you go, though, allow us to share a few final tips.

Avoid combining brands: Different manufacturers use different formulas, which may not be compatible.

Use a pH and EC metre: Measuring the pH and EC of your nutrient solution or growing medium will give you a clearer idea of the nutrient content in the root zone.

Fertilise regularly: Plants benefit from a steady, consistent supply of nutrients. Do not put off fertilising until signs of nutrient deficiency appear.

Unsure how to choose fertilisers, or just starting out with growing? You’ll find useful information for both beginners and experienced growers on our Higarden blog, or you can get in touch with our sales team.