Indoor plants need well-permeable soil that, depending on the type of plant, dries faster or slower. Find below how to create such soil and what to use to achieve the ideal substrate for indoor plants.
Water and air in the earth
Just as roots need water to function, roots also need oxygen.
When watering the plant, we literally push out all the air in the ground with water. When the soil is soaked like that for too long, when a certain amount of oxygen is not available to the roots – they begin to rot over time.
On the other hand, if the soil is so permeable that it does not hold water at all, an imbalance is created in the opposite direction, by having too much air around the roots, which, over time, causes the roots to stop functioning.
That is why it is important to create an appropriate balance between water and air, i.e. oxygen, in the soil around the roots.
In order to create that ideal balance between water and air, i.e. oxygen, it is important that when planting, we use containers with drainage holes and a good substrate that matches the plant we are planting.
Containers with drainage holes ensure that excess water, which the plant does not need, is not retained in the bottom of the container and thus damages the roots.
What makes a good substrate for indoor plants?
Depending on the type of plant, some require an extra permeable substrate that dries quickly, such as Orchids whose roots require a very breathable substrate.
This is precisely why Orchids are most often planted in bark that is very airy. If we planted the Orchid in very fine soil that absorbs and retains water very much, its roots would rot very quickly due to lack of oxygen.
On the other hand, some plants like to be planted in soil that absorbs a little more water, so they should be planted in a substrate that will retain a certain amount of water, and also be airy enough so that the roots get the amount of oxygen they need. needed.
Such a substrate is actually liked by most indoor plants.
The soil for indoor plants must consist of organic materials that absorb a lot of water (water binds to small particles of soil), such as peat and coconut bark, and materials that improve soil permeability, such as perlite, zeolite, vermiculite, etc.
These latter materials, in addition to allowing the soil to be more permeable, also have the ability to retain air (that is, oxygen) due to their porous structure.
By mixing such materials into peat or coir (any soil for houseplants that you can find in stores), we literally introduce a certain amount of air into our substrate.
Which materials promote better soil drainage and which are the best to use?
We will create the ideal soil permeability for most indoor plants by mixing – in volume, 70-80% absorbent material and 20-30% permeable material.
In order to create a more permeable substrate for our plants, we can use perlite, vermiculite, pumice stone, clay balls or zeolite. Each of these materials has different properties and depending on that, some will be more suitable for one type of plant and some for another. In addition, you can add some orchid bark to the substrate to create an even more permeable substrate.
These are porous materials that have (more or less) the ability to absorb and retain water, while simultaneously retaining oxygen.
In addition, some of these materials also have the ability to exchange cations (eng. CEC – cation-exchange capacity). This means that they have the ability to attract and retain the nutrients that we add to our plants in the form of fertilizers.
What they all have in common is that they help with soil drainage and bring air into the soil, thus creating a balance between water and oxygen. That is why it is important to add them to the soil for our green indoor plants so that they do not spend a long time in compact wet soil.
PERLITE
Perlite is a volcanic glass that, when heated at very high temperatures, explodes like popcorn, thus creating a permeable and light structure.
While using perlite, it is good to either wear a mask or lightly spray it with water, so as not to inhale fine volcanic glass dust.
What we achieve most with perlite is that we improve the drainage of the soil and, in addition, add oxygen to the soil.
Perlite does not absorb much water (unlike vermiculite, for example), so it dries very quickly. That is why it is ideal to use for those plants that like their soil to dry quickly.
In addition, perlite has a low cation exchange capacity, i.e. it does not have the ability to attract and retain nutrients.
CLAY BALLS
Clay balls are most often used either as decorative balls on the surface of the soil of indoor plants or placed at the bottom of the container to accelerate the drainage of water from the container.
You can also mix them into the soil to create better drainage and add oxygen to the soil.
Clay balls are a better choice for those plants that like their soil to dry out faster because they themselves dry out quickly.
Like perlite, they have a low CEC, that is, a poor ability to absorb nutrients from fertilizers.
KAMEN PLAVAC (PUMICE)
Increasingly, you can find a slightly more expensive option for soil drainage, which is pumice stone.
Pumice stone is a material of volcanic origin that, like perlite, expands when heated at high temperatures.
However, unlike perlite, pumice stone absorbs water well, so it adds water to the soil, as well as air, i.e. oxygen.
It dries more slowly, that is, it retains moisture for a longer time than perlite or clay balls.
Plumite also has a weak ability to exchange cations.
ZEOLITE
Zeolite is also a porous material that absorbs water well.
In addition, it has the ability to exchange cations, that is, it attracts and retains nutrients from fertilizers.
One study that tested zeolite and its benefits in agriculture showed that tomatoes grown in peat and zeolite (in a ratio of 70:30) produced more fruit, developed larger roots and thicker stems, and more leaves than those grown in 100% peat.
VERMICULITE
The vermiculite we use in horticulture is heated at high temperatures, thus obtaining a spongy structure that has by far the highest water absorption capacity of all the previously mentioned materials.
In addition to helping with soil drainage, it absorbs a lot of water and has the ability to retain nutrients from fertilizers.
It is recommended for plants that like moister (not wet) soil, that is, that do not like their soil to dry out quickly, such as Calathea, Maranta, Spatiphyllum, etc.