The primary function of a growing substrate is to provide a perfect environment for the normal development of the root system of our plants. To do this, the substrate must provide adequate anchorage to our plant, provide adequate amounts of water, nutrients and oxygen and be free of any substance that could be toxic to plants (phytotoxicity).

We can classify the substrates into:

  1. Organic materials;
    1. Of natural origin; they are subject to biological decomposition (peat and sphagnum moss).
    2. By-products and residues of different agricultural, industrial and urban activities. Most of the materials in this group must undergo a composting process, for their suitability as substrates (coconut fiber, rice husk, pine bark, sawdust and wood shavings, etc.)

B. Inorganic materials;

to. Of natural origin; They areobtained from rocks or minerals of various origins, often slightly modified by simple physical treatments (sands, gravels, volcanic lands, etc. ).

b. Physically modified; they are obtained from more or less complex treatments of minerals and natural rocks (perlite, vermiculite, expanded clay, rock wool, etc.)

The mobs.

They come from the partial decomposition of plants, mostly plants from swampy areas, due to a lack of oxygen dueto an excess of water. Basically they are plant remains in the process of fossilization.

They can be:

  • Blonde mobs; they usually belong to the upper area of the stratum and are the most recently formed. It is poorly decomposed and has excellent physico-chemical properties; fluffy structure, high porosity, high water retention capacity, good air content, low bulk density, acceptable cation exchange capacity and low salt content.
  • Black peat; it comes from deeper layers of the stratum and is therefore older and more decomposed. It has a lower quality than blonde mobs.

Among the physicochemical properties of peats are:

PARAMETER

BLONDE PEAT

BLACK PEAT

Bulk density

0.09 g/cm3

0.3 g/cm3

Porosity

90-95%

75-80%

pH

3,5

8,5

Cic

110 meq/100 g

250 meq/100 g

Carbon/Nitrogen Ratio

40

20

Nutrient levels

Low

Low

Aeration capacity

40%

20%

Readily available water

25%

30%

Reserve water

5%

6%

Water fully available

30%

35%

Water hardly available

25%

30%

Water holding capacity

700 ml/l

800 ml/l

Wettability

17 minutes

5 minutes

Contraction

20%

35%

Peat, apart from its excellent physico-chemical properties, presents another advantage which is to provide the plant with a certain stimulating effect due to the presence of substances of a hormonal nature and soluble humic substances. On the other hand, being a material of natural origin, marked differences can be found between different batches of product.

Coconut fiber.

Coconut fiber is a by-productof the coconut processing industry, in which coconut shells are processed to extract the fibers for various industries. Coconut shells go through a crushing process in which the longest fibers are separated into a range of particle sizes, according to the intended application. The leftover mixture of tiny fibers and powder is sold «as is» and used for horticultural purposes.

There are different granulometries; we will focus on the 1/4 and 3/4 inch ones. The first, thinner, we will use in seedbeds with small seedling and the second for cultivation.

Among the physico-chemical properties are:

PARAMETER

COCONUT FIBER

Bulk density

0.075 g/cm3

Porosity

96%

pH

5.5-6.2

Cic

70-100 meq/100 g

Carbon/Nitrogen Ratio

60-70

Nutrient levels

SODIUM AND POTASSIUM

Aeration capacity

55-60%

Readily available water

23%

Reserve water

4%

Water fully available

27%

Water hardly available

25%

Water holding capacity

750 ml/l

Wettability

<8 minutes

Contraction

15-18%

It is usually presented in plastic bags with dimensions of 100x18x16, 100x18x14 and 100x18x12 (between 26 and 28 liters of volume). It is also sold loose to fill any type of pot we have.

Among the advantages of coconut fiber over other substrates is its low bulk density, being easy to transport and handle. It also has a high C/N ratio which will give greater stability to the physico-chemical properties over time. The pH of this substrate is ideal for any type of plant.

The disadvantage is that, when coconut trees come from coastal areas whipped by marine winds, the material can have a certain content of salts, mainly sodium chloride; it is solved by washing the bag several times with good quality water before planting our vegetables until the outgoing water has similar electrical conductivity to the inlet.

Pine bark.

Pine bark is a term that includes both the material from the outer trunk area (floema), and the inner part (xylema). It can belong to different species of trees. In our area this bark comes mainly from pine and is a material that, like all those that come from natural origin, can present variability depending on the tree species (Aleppo pine, salgareño pine, black pine, stone pine, albar pine), at the age of the tree, the type of wood from which it comes (soft or hard), to the region where it is produced, to the type of soil and to the time of year in which it is collected.

Pine bark should not be used fresh since when composted it can demand large amounts of nitrogen, and also give off certain phytotoxic substances for our plants. The ideal is to acquire it already composted.

Among the physico-chemical properties are:

PARAMETER

PINE BARK

Bulk density

0.30 g/cm3

Porosity

80-85%

pH

3,5-5

Cic

80-160 meq/100 g

Carbon/Nitrogen Ratio

130-160

Nutrient levels

MEDIUM (phosphorus, potassium and calcium).

Aeration capacity

30%

Readily available water

13-18%

Reserve water

4-8%

Water fully available

17-26%

Water hardly available

10%

Water holding capacity

675 ml/l

Wettability

13 minutes

Contraction

9 %

It is worth noting the immunosuppressive properties that pine bark has with respect to certain fungi such as phythopthora, pythium, etc.

Sand.

Material of siliceous nature and variable composition depending on the components of the rock from which it comes.

They can be extracted from quarries or from rivers and wadis. The former are usually of more homogeneous composition and the particles are presented with live edges; the latter are more heterogeneous and the particles are usually rounded. The former are preferable when mixed with organic substrates since the edges make the sand not deposit at the bottom of the container.

In any case, it is preferable that they are free of silt, clays and calcium carbonate since over time these materials are dragged to the bottom of the container, accumulating and negatively affecting the hydro-physical characteristics of the substrate.

Sands are characterized by good drainage and low water holding capacity, butthese qualities do not mean that they persist when sand is mixed with organic substrates.

Sand is a strong substrate and is used to increase the bulk density of the material with which it is mixed and, therefore, increase its wettability.

Due to its mechanical hardness it is a practically permanent substrate.

Among the physico-chemical properties are:

PARAMETER

GRAVEL (2-20 mm)

Sand (1-2 mm)

Bulk density

1.55 g/cm3

1.60 g/cm3

Porosity

40%

40%

Aeration capacity

35%

20%

Water fully available

2,5%

19%

Perlite.

Perlite is an aluminum silicate of volcanic origin. Perlite particles have a rough surface that allows you to retain water in it; it only retains water on its surface so it is used to provide aeration to substrate mixtures.

It is an inert material that does not break down biologically or chemically. It is formed by aluminum oxide and silicon oxide so we have to control very well the pH of the irrigation solutions that we use since an excessively acidic solution can solubilize the aluminum, creating phytotoxicity problems in our plants (pH 6.5-7.5). It can degrade during the growing cycle, accumulating at the bottom of the substrate container.

The cation exchange capacity of perlite is very low; around 3 meq/100 g; thisfactor makes us take special care in the fertilizers since the various nutritional elements that we provide, will hardly be retained in the substrate. The main advantage of growing in perlite, compared to other substrates, is the ease and simplicity of maintaining an almost constant moisture profile. Also the white color reduces the root temperature in very hot conditions.

Before planting, an initial saturation must be carried out dthe perlite container; consiste in carrying out various irrigations with our pre-established nutrient solution for the crop that we are going to develop, at a pH and an adequate E.C. It should be saturated little by little and not suddenly.

Among the physico-chemical properties are:

PARAMETER

PERLITE B12

Bulk density

0.143 g/cm3

PH

6,5-7,5

Porosity

85%

Aeration capacity

30%

Readily available water

25%

Reserve water

7%

Water fully available

32%

Water hardly available

25%

Worm humus.

It is the result of the transformation of composted organic matter by California redworms. The result is an organic matter of neutral pH that acts as a fertilizer (to some extent) and above all as a soil regenerator.

It has good levels of macronutrients (nitrogen, phosphorus, potassium, calcium, sulfur and magnesium) and micronutrients (zinc, iron, copper, molybdenum and chlorine) and a pH between 7.5 and 8.5.

It offers a rich and varied microbial flora and a huge range of phytoregulators, which work to improve the natural fertility of the soil.

It recovers depleted soils and is not toxic to plants, animals or humans. It provides a nutritional balance to plants because it contains substances that are released slowly.

Improves the physical properties of the soil.

Ayuda to retain moisture in yourstrato for longer.

Itprevents the compression of clay soils and contributes to improving sandy soils.

Akadama.

They are clay granules of volcanic origin found only in Japan. It is a very porous substrate that retains water well (ideal for plants that need a good water supply) but allows excellent aeration of the root. There are different granulometries and the pH ranges between 6.5 and 7.

Kiryuzuna.

It is a material formed from the cooling, when reaching the sea, of a volcanic eruption. It is of small granulometry so it allows a good drainage of the water. Its pH ranges from 6.5 to 6.9.

Moss sphagnum.

Substrate of plant origin comprende a genus of mosses called peat mosses. They come from northern areas of humid tundra. It has a high water and nutrient retention capacity. Widely used in orchids and vertical cultivation.

The ideal substrate.

Theoptimal levels of the physico-chemical properties of the ideal substrate would be the following:

PROPERTY

OPTIMAL LEVEL

Particle size

0.25-2.5 mm

Bulk density

<0.4 g/cm3

Total porous space

>85%

Water retention

-10 centibars 55-70%

-50 centibars 31-40%

-100 centibars 25-30%

Aeration capacity

20-30%

Readily available water

20-30%

Reserve water

4-10%

Total water available

24-40%

Volume contraction

<30%

pH (saturated paste)

5,2-6,3

Electrical conductivity

0,75-1,99

Cic

>20 meq/100 g

C/N ratio

20-40

ASSIMILABLE NUTRIENTS IN SATURATION EXTRACT (ppm saturation extract)

 

Nitric nitrogen

100-200

Ammoniacal nitrogen

0-20

Phosphorus

6-10

Potassium

150-250

Calcium

>200

Magnesium

>90

Iron

0,3-3,0

Manganese

0,02-3,0

Molybdenum

0,01-0,1

Zinc

0,3-3,0

Copper

0,001-0,5

Boron

0,05-0,5

Rarely does a material alone meet the most suitable physical, chemical and biological characteristics to consider it as the ideal substrate. In most cases they must be mixed or combined with other materials in different proportions to adapt it to the required conditions.

Let’s first distinguish between combining and mixing substrates:

  • To combine is to arrange different substrates in an orderly way in a container or pot. In the lower area we will put the material of greater weight to give stability to the pot (gravel, boulders, etc.). In the intermediate zone, whereour roots will develop, we will put that material that best suits the plant in terms of water retention and aeration (peat, coconut fiber, sphagno moss, etc.). Finally, in the surface area we will put materials that prevent the loss of water and heat (pine bark, pruning remains, etc.).
  • Mixing substrates is stirring different materials until a homogeneous mixture of them is reached. Rarely does a material alone meet the most suitable physico-chemical and biological characteristicsfor certain growing conditions. In most cases it is necessary to make mixtures of different substrates. A very important aspect to take into account is that, by mixing materials of different granulometry, the finer material will occupy the space between the particles of the thicker material, leading to a decrease in porosity and volume. Whenever several materials are mixed, we must pay attention to the homogeneity of the resulting mixture.

The mixture of organic materials with blonde peat results from the best substrates.

If we combine we will do it in layers, and each layer of substrate will maintain its physico-chemical properties. On the other hand, when mixing we will give rise to a new type of substrate whose properties will depend on the properties of the components and their percentage in the mixture.

As for the mixtures, for me thes that I likethe most and the best results I have given are the following:

  1. 50% blonde peat, 25% perlite and 25% worm humus.
  2. 70% blonde peat and 30% perlite.
  3. 50% blonde peat and 50% perlite.
  4. 50% coconut fiber, 25% perlite and 25% worm humus.
  5. 70% coconut fiber and 30% perlite.
  6. 50% coconut fiber and 50% perlite

If we provide humus we will have a contribution of certain nutrients for some time. Once it has been completely mineralized, it does not provide nutrients. A little organic matter comes in handy for certain plants.

If we want to manufacture a substrate for seedbed we will use:

  • 50% blonde peat or coconut fiber.
  • 50 % perlite.

If instead we want a substrate evento cuttings we will mix:

  • 50% blonde peat or coconut fiber.
  • 50% sand.

If we have acidophilic plants (those that need a substrate with low pH) we will mix:

  • 50% Blonde peat.
  • 30% perlite.
  • 20% worm humus.

For crassulaceae and cacti:

  • 50% akadama.
  • 30% blonde peat.
  • 20% perlite.

Para bonsai:

  • Akadama 70%
  • Kiryuzuna at 30%.

We have not mentioned any mixture that contains natural soil (what we call «terraced land») since I want this blog to be intended mainly for those who grow in your homes; if someone has the possibility of easily accessing this type of land, one of the best mixtures is the following:

  • 40% land
  • 20% blonde peat or coconut fiber
  • 20% worm humus
  • 20% perlite.