Types of Substrate and How to Prepare Them – Complete Guide

Translated by Nick R

If you want to get into the gardening world and have your own garden, you need to know about the substrate. After all, your plants will grow on it, and by knowing how they work, you will be able to give your plants all the necessary nutrients.

For this, we bring you this guide with everything you need to know about substrates. You’ll learn what their function is, what properties they have, what types of substrates exist and we’ll even give you a selection of special substrate mixtures for specific plants.

What are substrates and what are they used for?

When plants are sowed directly on the ground, they have more space to grow freely. However, when we have to plant in pots, especially for home gardens, the plants need specialized care.

Similarly, all plants have different characteristics and requirements depending on the habitat where they belong. So, if we want to have certain species in our garden or vegetable garden you should provide them with the necessary conditions to survive.

This is where we start talking about substrates, which are different growing soils to the ones we normally have in the garden since they will have other added components that allow the plant to grow in a more aerated, lighter environment and with more organic matter.

Soil types

Therefore, in case you use garden soil, you first need to recognize the types of soil in order to identify yours based on its texture and make the necessary modifications:

Sandy: Coarse mineral particles. It’s rough, dry to the touch and doesn’t retain water well. It’s a light soil that is easy to work, aerated, but with little water and nutrients.
Loamy: Medium mineral particles. It is dark brown colored, softer to the touch and holds water and nutrients better. It favors the air/water balance depending on the good or bad structural conformation.
Clayey: Small mineral particles. With fine yellow grains, it’s a rather heavy soil with waterlogging problems and lack of aeration, even forming puddles, although it has a good capacity to retain nutrients.

Why use substrates in your garden

Now, some of the reasons to use substrates include:

Because of the need to pot plants either for indoors or because they need to be carried for maintenance. For example, those outdoor plants that must be moved from place to place when temperatures change.
Due to the lack of nutrients in the natural soil, we need to make adjustments so that the plant adapts and has similar conditions to its original habitat.
To have better control of water supply and humidity according to the requirements of each plant.
For better comfort of potted plants and to encourage the root development they need, despite the limited space.
To ensure significant plant growth and vitality. This is because they develop depending on the adequate supply of nutrients provided by the substrate.

Substrate properties

Substrates have physical and chemical properties that allow them to provide the ideal habitat for our plants.

Physical properties of substrates

Among the physical properties we can find:

Porosity, which refers to the presence of air in the substrate, allowing it to be a light material with good aeration.
Density, which has to do with the components that make up the substrate, both solids and air spaces.
Granulometry, which is about the size of the particles or fibers that form the substrate. These influence the behavior of the substrate when moisture is present, which will determine its water-holding capacity.
Structure, which can be granular or fibrillar. In most cases, it’s granular since it has no stable shape and easily adapts to the container. When it’s composed of fibers it gets more rigid and less treatable.

Chemical properties of substrates

Chemical properties are those that facilitate the degradation of the materials that make up the substrate. Likewise, they help in the transference of nutrients to the roots of the plants. Among them are:

The pH (Potential of hydrogen), is important for the adequate development of the crops and to achieve high yields. It is a key property because nutrients can be added to the soil, but if the pH is not appropriate, the roots won’t be able to absorb them.
EC (Electrical conductivity), measures the concentration of soluble salts present in the substrate. It’s recommended that the EC is low to facilitate fertilization and avoid toxicity issues in the crop.
CEC (Cation-exchange capacity), which refers to the capacity of the substrate to retain and exchange nutrients.

There are also chemically inert substrates, which help to support the plant but don’t provide additional nutrients. Therefore, it is important to add separate fertilizers.

These include sand, pea gravel, perlite, expanded clay and rock wool.

On the other hand, there are chemically active substrates that provide support for the plant and are rich in nutrients. Something interesting is that they store nutrients and release them according to the needs of each plant.

These include peat, vermiculite, and tree or pine bark.

6 Natural substrates

These are substrates that come from nature and do not usually require treatment before use. Here are 6 types of natural substrates.

Sand

This is one of the most commonly used because of its ease of use, porosity, granulometry and because it provides good drainage. River sand, which, unlike sea sand, doesn’t contain salts, is advisable for this purpose.

Its water retention capacity is average but over time it loses aeration capacity. Its pH varies between 4 and 8.

Sand is heavier than most of the components of a substrate so it cannot be used on its own, but mixes well with other materials. It’s also low in nutrients, so it has zero cation exchange and is chemically and biologically inert.

It’s preferable to wash and sieve it before use. Primarily to ensure its purity, water drainage capacity, and that it doesn’t condense after a good watering.

Gravel

Gravel is derived from different kinds of rock and it’s composed of small and large particles. The former and smallest ones are known as tepojal, gravel, or pebbles. The larger particles are known as stones or cobbles; however, they have low moisture retention. Thus, they are not highly recommended as a substrate for agricultural or hydroponic farming.

This item has a rough appearance, dark color, and a hard structure. It can be found in fragments of about 2 to 64 millimeters in diameter.

The gravel is most commonly used as a substrate for plants like pumice and quartz. However, some types of gravel, such as pumice or river sand, should be washed before use.

In general, they have good structural stability; although their water retention capacity is low, their porosity is high. There are substrates such as gravel or volcanic soil rich in alumina, silica and iron oxide. Its pH is slightly acid, it’s very steady, has good aeration, and very good water drainage.

Peat

On the one hand, there is black peat, a substrate that comes from the organic matter decomposition of swamps and peat bogs over many years. The result is a material low in nutrients, but that in conjunction with a fertilizer becomes ideal for the sowing of almost all types of plants (vegetables, trees, flowers, etc.).

Its PH is high, between 7.5 to 8, it’s formed in low areas and as it is more decomposed, it’s darker in color.

On the other hand, blond peat is formed in low-temperature areas with a high precipitation rate. Generally composed of moss debris, they have a higher organic matter content and have better aeration, as well as better water retention capacity. This allows to maintain the soil structure and reduce the watering frequency.

Its PH is acidic, between 3 and 4, since it is formed on the surface of swamps with low-temperature conditions, little sunlight and frequent rainfall. The physical and chemical properties of blond peat depend on its components and on the characteristics of the place of origin.

For this reason, it should be mixed with other substrates that favor the enhancement of the peat’s properties. This way, you can ensure a successful production, better results and high-quality products.

Tree bark

Different types of bark are used, but the most popular is pine bark. It’s a light substrate, with excellent porosity and aeration. It helps to retain moisture and even prevents the development of weeds, therefore it is also used as ~~mulch~~.

It should be used preferably as compost and not raw as it can be toxic. Additionally, the water retention capacity is medium to low, and the PH varies from slightly acidic to neutral.

Tree bark is a very resistant material that, if you need to, you can step on with no problem. It works fine for creating a color effect with plants you have in the garden, creating paths, and separating some areas. Note that you can also use wood chips or sawdust.

Worm humus

It’s one of the best available organic elements as it supplies nutrients to plants in the long term. It also increases and enhances soil structure, as well as working as a natural anti-pest and anti-disease agent.

In addition, earthworm humus can increase water retention capacity, favors soil cation exchange, helps to increase the effectiveness of mineral fertilizers, and other processes.

The use of worms for soil is known as vermicomposting or vermiculture. Its effectiveness lies in the fact that the worms’ digestive system harbors certain microbes’ species that better bind nutrients, and which are later expelled in the excrement and are more easily absorbed into the soil.

It’s a dark-colored, odorless element that leaves no residue when touched. You can use it in almost any type of crop as it is very rich in organic matter and has a neutral pH.

Coconut fiber

Coir fiber works as a substitute for peat or is often mixed with it. It stands out for its ability to provide a base with excellent aeration and drainage for plants. In addition, it’s perfect to be used together with other organic elements that contribute nutrients.

Clearly, as it’s a natural and ecological product, it’s free of chemicals, but must be washed before use due to its salts. It also works as a fungicide, and its neutral, slightly acidic pH is between 5.5 and 6.5.

Coconut fiber helps in vegetable production in greenhouses, gardens and nurseries, it also helps to reduce the damage that occurs in marshes and wetlands. Because it is lightweight, it can be used in all types of locations and structures.

It helps plant roots to develop easily and can absorb or transfer warmth. This favors root development in the hot and cold seasons of the year.

Coconut fiber can be found in 3 presentations according to its granulometry; the first one is fine coconut powder or coco peat; the second is coarse, as it’s found in small pieces; and the third is chip, which is a larger piece.

Artificial substrates

They are named in this way because they go through physical procedures to obtain them from the modification of a natural material. Now, we’ll mention 5 types of artificial substrates.

Perlite

Perlite comes from volcanic gravel. It has good moisture retention and enhances air circulation, but doesn’t provide nutrients by itself. It’s inert and PH neutral, so it doesn’t react with any element in the soil and doesn’t alter its balance.

Perlite is very dusty when dry and tends to float to the top of a container during watering. You should be careful to avoid breathing in this dust as it is somewhat toxic.

This mineral is widely used in gardening because it is very light, free of pests, diseases, and weeds, non-flammable, and, finally, its white color helps to reduce the substrates’ temperature and increase the reflection of light.

Perlite can be used in other activities besides gardening, some of these are:

Ceramics and glass industry
Filter manufacturing
Electrode manufacturing
Cement and concrete production
Mining industries
Metallurgical operations

Vermiculite

It’s obtained from minerals such as mica. It has good aeration, although it tends to compact with time. It has a high water-holding capacity, even more than perlite, and contains potassium, calcium, ammonium and magnesium.

Although vermiculite is not as resistant as sand and perlite, its chemical and physical properties are highly desirable. It contains a high cation exchange capacity and its pH is also neutral, between 7 and 7.2.

It’s a very light, economical, inert element (i.e. it does not contain pests or seeds). It can be used in hydroponic crops, seedbeds, pots and plants sold or transported in bags.

Expanded clay

It’s obtained after the treatment of clay nodules. It has a high porosity level, but low water retention. That said, it tends to be mixed with peat or other components to improve soil drainage. Its PH is between 5 and 7.

Also known as arlite, it is usually round in appearance and the size of its granules is very variable, however, it’s generally between 10 and 16 millimeters. It favors the aeration of the roots and the water flow in them.

It has the ability to maintain its physical structure and properties for a prolonged time. It can be mixed with other elements such as peat to favor drainage and aeration.

Rock wool

Made from volcanic rock. Its chemical composition includes components such as silica and oxides of aluminum, magnesium, iron, and calcium. In addition to its aeration capacity and water retention. It is not biodegradable but has excellent porosity.

Its physical structure is a plate or cube shape with a fibrous structure. It’s a substrate normally used in hydroponics, a cultivation method in which the plants are in mineral dissolutions and not in soil.

It lasts for a limited time, so it’s functional for about 3 years. After this time, its properties are lost and must be replaced to ensure opportune plant growth.

Expanded polystyrene

It’s obtained by processing polystyrene. Highly resistant to decomposition, it’s white in color, very light, has low water retention, increases aeration and drainage, and decreases bulk density.

However, it disposes of organic matter and is non-biodegradable. Therefore, its common use is often due to its low cost and a pH slightly higher than 6.

How to prepare the ideal substrate?

Well, now that you know the components and their characteristics, we’ll show you how to prepare specific substrates for certain plants.

Universal substrate

Initially, we’re going to prepare the best substrate for all types of plants, except for succulents. You should keep in mind that the 3 essential aspects to prepare a mix that favors plants are:

Humidity
Nourishment
Drainage and aeration

That said, for moisture, you can go for coconut fiber or peat moss. For food and nutrients, you’ll need worm hummus which you can buy in garden stores or even florists. Finally, for water drainage and aeration, you can use either perlite or vermiculite.

Now, you’ll just need to mix equal parts of the elements for moisture and food and 1⁄5 for drainage. In percentages, it would be 40% coir fiber or peat, 40% humus, and 20% perlite or vermiculite. The quantities will depend on how much substrate you need to prepare.

This type of substrate is recommended for both outdoor and indoor growing. As you could observe, it works thanks to its high degree of moisture retention, good organic matter composition and good water retention.

As an extra tip, if your plants require more humidity, you can choose to add only 10% of perlite or vermiculite.

Substrate for succulents

Due to the succulents’ needs, we must prepare a light substrate with low humidity and without water stagnation.

Therefore, we’ll implement perlite, river sand, and prepared soil, which already comes with nutrients and you can get them in gardening stores or flower shops. However, the natural soil that you have in your garden will also work.

You must mix equal parts of all the elements. As a tip, it’s preferable to wash the sand before using it; simply pass it through a strainer until the water comes out clean.

As another option, you can choose to use sand (either river, beach or construction sand, but remember to wash it), shavings or sawdust, and coconut fiber. You should mix all the ingredients evenly.

If you wish to provide it with some additional nutrients, you can add some crushed eggshells.

Substrate for pots

If you want to prepare a substrate for your vegetable garden plants or for those that are going to be planted in pots, we recommend the following mixture.

You’ll need black or prepared soil, perlite or vermiculite, and worm castings. You’ll have to use 40% of prepared soil or 30% of natural soil and supplement it with 10% coconut fiber to provide more nutrients.

Then add 10% or a bit more of worm humus and the remaining 50% will be perlite or vermiculite. Remember that you can also choose to use 25% of each.

Substrate for carnivorous plants

If you have or want to introduce this type of plant in your garden, we invite you to read our article on carnivorous plants so that you know all their qualities. In the meantime, here we tell you what is the special substrate for these beautiful plants.

In this case, we’ll use peat and perlite or vermiculite. It is particularly ideal for seed germination. What you should do is mix 50% of peat and 50% of perlite or vermiculite, although you can also use both ingredients for aeration using 25% of each one.

We hope this article has allowed you to better understand and learn about substrates and their functions. As you could have observed, it is an essential element in gardening as it allows us to recreate the best habitat for our plants so that they grow at their best.