How to Choose a Potting Substrate

In our complete guide to choosing a suitable garden substrate we present the most important information about the composition of garden substrates, their proper use and recommend the best brands and mixes for growing plants indoors and outdoors, in pots and in beds or under artificial lighting.

Garden substrates are growing media intended for cultivating plants in soil by traditional methods. Their main use is for growing plants in pots both indoors and outdoors or as soil for beds or greenhouses.

Read also: Guide to growing substrates

What do garden substrates contain?

Manufacturers adjust the composition of garden substrates so that the resulting mixes have different properties in terms of water retention, nutrient content or soil acidity.

The basic component of every garden substrate is organic materials of plant or animal origin. These most commonly include peat, coconut fibers, composted wood and tree bark, compost, worm humus and other materials that serve as a source of organic nutrients for plants.

Another ingredient is inorganic natural materials that ensure substrate aeration, improve drainage and help retain moisture. These include perlite, vermiculite, expanded clay, sand and others.

Many garden substrates are enhanced with fertilizers, whether mineral slow-release types or organic soil supplements like bat guano, bone or blood meal, alfalfa or seaweed extracts.

Other additives, for example lime and substances to balance pH, beneficial microorganisms (Trichoderma, mycorrhizal fungi) or other admixtures further adjust the specific properties of the substrate.

How to choose a garden substrate?

The choice of garden substrate depends mainly on the age of the plants and your growing method. Generally, for seedlings and young plants both indoors and outdoors, unfertilized or lightly fertilized mixes are most suitable. Garden mixes with a higher fertilizer content are used as a medium for nutrient-demanding plants, indoor cultivation or as soil for beds or greenhouses. For some growers, the purely natural origin of all components may also be important, for example for organic cultivation or in organic farming.

Unfertilized garden substrates are made only of a clean mix of organic and inorganic materials without added fertilizers. They are suitable as a starting medium for germination, cuttings, seedlings or young plants intended for later transplanting. When growing in unfertilized garden substrates, it is necessary to supply nutrients to the plants in the form of fertilizers, whether organic or mineral.

• Plagron Promix
• Canna Terra Professional
• Gold Label Custom Mix (zemina/kokos)

Lightly fertilized garden substrates, sometimes referred to as “light-mix”, contain only a minimal amount of nutrients in the form of mineral or organic fertilizers. They are suitable either as soil for young plants intended for later transplanting, rooted cuttings or for growers who want to supply nutrients according to their own preferences and needs. Lightly fertilized mixes can be combined with most commonly available fertilizers and feeding programs.

• BioBizz Light Mix
• Plagron lightmix s perlitem
• Atami Janeco lightmix
• Gold Label Special Mixlight

Pre-fertilized garden substrates are balanced mixes with a moderate amount of nutrients that will sustain plants for the first weeks to months of life depending on species, pot size and growing method. They are suitable as a basic substrate for growing in pots indoors and outdoors, however in later stages it is necessary to provide plants with nutrients in the form of mineral or organic fertilizers.

• Plagron Growmix s perlitem
• Plagron Allmix
• BioBizz All Mix
• Canna Terra Professional Plus

Heavily pre-fertilized substrates contain a high dose of nutrients in mineral or organic form and are not suitable for seedlings, cuttings or young plants because the high nutrient content in the soil can cause “burning” of leaves and roots. Heavily pre-fertilized mixes are suitable for nutrient-demanding plants, as soil for beds or greenhouses and as a medium for indoor cultivation under very intensive artificial lighting.

• Plagron Royalmix
• Plagron Batmix
• Atami Kilomix
• Monkey Super Soil
• Guanokalong Complete Mix

Substrates intended for organic cultivation contain only materials of natural origin and are often certified for growing plants in BIO quality without the use of mineral fertilizers and chemical pesticides. These substrates can be pre-fertilized or unfertilized and are suitable for cultivating plants in pots indoors and outdoors or as soil for beds or greenhouses.

• Canna BIO Terra Plus
• Atami Bio Growmix
• Terra Aquatica Organic Soil Light-mix
• BioNova Bio Soilmix

Vegan substrates are similar to substrates for organic cultivation in that they are made only from natural materials, with the difference that they contain only plant-based components. These mixes are suitable for growing in pots indoors and outdoors or as soil for beds or greenhouses.

• BioNova Bio Soilmix

Substrates for sowing and germination contain a minimal amount of nutrients and have a finer structure to retain more moisture, and are used for germinating seeds and rooting cuttings.

• Canna Terra Seed Mix

Special substrates are designed to meet the specific requirements of certain plant types. Among them you can find substrates for citrus, orchids, substrates for roof gardens or herbs.

Answers to the most frequently asked questions about garden substrates

Is it possible to use garden substrates for multiple growing cycles in a row?

Used growing substrate can be refreshed and reused; however, if done incorrectly there is an increased risk of pests, diseases or molds. In indoor cultivation it is common practice to replace the growing substrate with new substrate after each cycle. In outdoor cultivation in pots or beds it is possible to rejuvenate the soil before planting by adding compost, worm humus or a heavily pre-fertilized garden soil mix.

Do I need special fertilizers when growing in garden substrates?

Garden substrates may or may not contain a certain amount of fertilizers that serve as nutrients for plants. Especially when growing in pots, plants can quickly deplete nutrients from the soil and after some time it is necessary to replenish them. Various types of fertilizers are available for this purpose, from fast-acting mineral ones to fully organic options. The choice of the right feeding program then depends on the plant species and your growing style.

How often should plants grown in garden substrates be watered?

The frequency and amount of watering depend on many factors, but in general for plants grown in beds the substrate should be watered when the soil has dried to a depth of about one inch. For plants in pots we can estimate the amount of water in the growing medium by weighing or feeling the pot.

Read also: Dry or liquid fertilizers — which are better for indoor growing?