Guide to Growing Substrates

Growing substrates are essential for successful plant cultivation, whether in a home environment or in professional agriculture. From traditional soil mixes to modern coconut substrates or mineral wool – each type of growing media has its specific characteristics and uses. Explore with us the advantages and disadvantages of individual growing substrates and find the most suitable one for your plants.

We refer to a growing substrate as a material or mixture intended for plant cultivation that serves as a medium retaining water, air, and nutrients absorbed by plant roots. A growing substrate can consist of organic materials such as soil, coconut fibers, clay pellets (expanded clay) or inert materials such as perlite, vermiculite, or mineral wool (rockwool).

Coconut substrates

Coconut growing substrates are made from finely shredded coconut fibers and coconut husks. The added value of this growing media is that it combines the benefits of soilless and soil-based substrates, making it versatile in use. You can use coconut growing substrates for pot cultivation with hand watering or irrigation systems, outdoors in beds, and in greenhouses.

If you choose coconut as your growing medium, you will need water-soluble fertilizers for preparing a hydroponic nutrient solution. Pure coconut substrate contains no nutrients on its own and serves only to anchor roots, which you must supply with water and nutrition. Coconut substrates retain water well while protecting plants from overwatering, making them a suitable medium even for beginners. The only thing to watch is not to let the coconut substrate dry out completely, because it will lose its water-retention ability.

Advantages: neutral pH, supports growth of beneficial bacteria and fungi, excellent retention properties, versatile use

Disadvantages: zero nutrient content, poor-quality blends may contain high salt levels, some coconut substrates must be pre-buffered before use

Rockwool

Rockwool is mineral wool made from melted basalt rock, which is then formed into cubes or slabs. The result is an inert medium that retains both water and air very well and is ideal for hydroponic cultivation, seed germination, and cuttings. Standard rockwool is manufactured so that 18% of its volume is reserved for air, even when fully saturated. At the same time, mineral wool dries evenly, so plant roots constantly have access to water.

As with other soilless substrates, mineral wool contains no nutrients and plants must be fed using hydroponic fertilizers. Rockwool itself has a high pH, so cubes or slabs must first be soaked in an acidic solution at pH 5.5 before use. First adjust the pH of standing water to the desired value using acid for lowering pH and then rinse the medium thoroughly. From that point on, the nutrient solution pH should not exceed 6.1 to compensate for the alkalinity of the mineral wool.

Advantages: inert and sterile substrate, high capacity to retain water and air, reusable

Disadvantages: can irritate skin and eyes if handled carelessly, pH adjustment required, contains no carbon for microbial life

Expanded clay (LECA)

Expanded clay (LECA), also known as LECA, is a porous material produced by heating clay to high temperatures. It resembles small lightweight pebbles and can be used as an additive to soil in various types of hydroponic systems (run-to-waste, DWC, NFT, ebb and flow, drip irrigation) or as a medium to anchor plants in aeroponic cultivation.

If you use expanded clay as a standalone growing medium, you must supply all nutrients to the plants via the irrigation water in the form of water-soluble hydroponic fertilizers. Also, similar to rockwool, the growing substrate should be rinsed first and the nutrient solution pH monitored carefully throughout the cultivation cycle.

Advantages: does not decompose, neutral pH, retains water and nutrients, good aeration of the root zone

Disadvantages: can irritate skin and eyes if handled carelessly, pH adjustment required, contains no carbon for microbial life

Perlite and vermiculite

Perlite and vermiculite are produced by heating rock to high temperatures. Perlite results in a bright white grit from lightweight stone. Vermiculite has a slightly finer structure and an ochre color. Perlite and vermiculite are used as additives to garden and coconut substrates, for seed germination and cuttings, or as a medium in hydroponic systems using irrigation systems.

Perlite and vermiculite are inert substrates, so all nutrition must be provided to plants in the form of a hydroponic nutrient solution. Vermiculite differs from perlite in that it has a higher capacity to retain water and nutrients and decomposes over time, which may slightly raise pH around the root zone. Perlite is more durable and does not decompose or affect root zone pH, but it has minimal capacity to retain water and nutrients.

Advantages: sterile, nearly or completely neutral pH, good air access to roots

Disadvantages: non-renewable resource, irritating dust, fine particles can clog irrigation systems

Soil-based garden substrates

Soil-based garden substrates are a traditional growing medium that can take many forms. Seed mixes for germination or cuttings, light mixes for the first weeks of plant life, moderately and heavily fertilized mixes or soil blends suitable for organic cultivation. Garden substrates can be used for pot cultivation with hand watering or irrigation systems, outdoors in beds, and in greenhouses.

The main advantage of soil as a growing medium is its natural nutrient content, and manufacturers may also add fertilizers to the mix that serve as nutrition for plants in the first weeks after planting. When growing in soil substrates you can use fertilizers for soil cultivation, including mineral salts in the form of nutrient solution, powder, or slow-release pellets. You also have the option to grow entirely without chemicals using purely organic fertilizers. Thanks to high buffering capacity, soil mixes can handle pH fluctuations better than other substrates, making them a suitable choice for beginner growers.

Overview of growing substrates