Ecological substrates and natural fertilizers for garden plants

In organic farming it is essential to use suitable substrates and fertilizers, organic substrates and natural fertilizers that do not have chemicals and that allow plants to grow healthy and strong.

Here we see various types of planting substrates

Characteristics of ecological substrates

To be able to say that we are using an “ecological substrate”, first of all it must lack any type of synthetic chemical fertilizer (it must be used to fertilize it with organic or natural fertilizers) and it must not have been subjected to any artificial disinfection (radiation ionizers to disinfect the soil, for example, are not allowed in Organic Farming).

In addition, the use of ecological substrates has positive effects or benefits for the conservation of the environment. For example, ecological substrates are those:

  • Recyclables: by-products from other activities or industries that are themselves biodegradable or recyclable.
  • That limit the development of pathogens, which often prevents their treatment with artificial chemical products: composted pine bark to prevent/eliminate some diseases caused by fungi.
  • That prevent the washing of nutrients.
  • That optimize water consumption: substrates with high water retention and cation exchange capacity.

Most common substrate components

  • PEAT

We will devote another article to explaining how to properly choose and/or combine the different materials and the techniques for preparing and maintaining the substrate.

You also have more information about the suitable characteristics of the substrate in this post that I wrote about the “ideal substrate”.

Natural fertilizers: ecological fertilization

We have already seen that, in addition, if it has been a while since we established the orchard or if the nutrient supply of the substrate is low, we must fertilize it. We are going to see the different fertilizers or fertilizers that we can use in our organic garden.

– Organic fertilization: compost, green manure, manure, liquid manure…

the compost

It is the most widely used fertilizer in organic farming. It is very interesting because we can make homemade compost ourselves (so we save ourselves having to buy fertilizer) and we also take advantage of domestic organic waste and that of the garden itself.

Compost to fertilize the organic garden. On the left: mature compost, on the right: compost in formation

Composting is a technique of controlled decomposition of waste to obtain humus. This transformation is a biological decomposition, that is, it is carried out by microorganisms (fungi, bacteria and small insects or arthropods) so the conditions (humidity, temperature, air, size of the residues, process time, etc.) have to be within limits. (We will dedicate an article to the technique of traditional composting).

We can also buy industrial compost or, as an alternative to traditional compost, use vermicompost or worm compost, obtained thanks to the action of the California red worm (Eisenia foetida).

green manures

They are crops of different fast-growing plants (legumes, grasses, cruciferous plants…) that are sown, cut and buried to improve the properties of the soil. Not only do they fertilize the soil with the humus that comes from buried organic matter, they also improve its structure and favor the growth of populations of beneficial microorganisms.

Clovers to use as green manure

The crops most used as green manure due to their rapid growth and the amount of nutrients they provide are: legumes such as clover, alfalfa, vetch, peas, broad beans, lupins…cereals or grasses (normally associated with legumes) such as rye, oats or barley, and some cruciferous crops such as fodder rapeseed, white mustard or fodder radish.

Nutrient content of crops used as green manure and recommended dose

For adequate humus production, the crop should be cut between flowering and fruit formation, and buried, not immediately but after aerating for a few days.

Instead of burying the waste, we can also use it to create a vegetable cover or mulch, which will protect the soil.


Waste from extensive livestock or extensive ecological farms is used. The most used are manures from: cattle, sheep, goats, horses, pig slurry, chicken manure, guano…

Proper handling of the manure before its application to the soil is very important to favor the formation of a good humus, the absence of weeds, seeds or pathogens and to avoid the loss of nutrients. Before it is added to the soil it must be «matured» in a well-compacted, oxygen-free heap (anaerobic) or in a composter under aerobic conditions.


There are many types of peat from peat bogs, where sphagnum moss accumulates. This organic fertilizer is composed of organic matter, water and minerals. In addition to providing organic matter, it improves the structure of the soil and favors the slow release of nutrients. It is a non-renewable natural resource, since the rate of extraction of peat reserves is higher than that of natural generation.

Prepared organic fertilizers and humic amendments

There are many types of natural organic fertilizers already prepared from algae, vegetable remains… They can be liquid or solid (crushed).

We must ensure that the product is suitable for use in organic farming, since not all natural products are. You have to follow the manufacturer’s recommendations and pay attention to whether it is a fertilizer for application in the substrate or in the leaves of the plant.

– Mineral fertilization

Starting from the fact that organic fertilization is essential due to the contribution of nitrogen, microorganisms and because it favors the structure of the soil, it is also possible to use mineral fertilizers to complement it and supply any deficiency, directly providing useful nutrients for the plant.

In organic farming, mineral fertilizers must be natural: synthetic products cannot be used, nor with the addition of chemical products.

Below are the types of natural materials for natural fertilization allowed in organic farming according to the most important nutrient they provide:

  • Potassium: wood ash, potassium salts such as sulfates or potassium chloride (sylvinite, carnallite, kainite…)
  • Phosphorus: Calcined natural phosphates (such as aluminum calcium phosphate, which also provides aluminum and calcium), Thomas’s slag…
  • Magnesium and Sulphur: the amount supplied to the soil with organic fertilization is usually sufficient, but if it is not enough, natural mineral amendments can be used from dolomite, magnesite, epsonite (with magnesium) or sulfur.
  • Silicon: crushed siliceous rocks.

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