How to improve the drainage of a substrate with perlite

One of the biggest problems we encounter when growing in pots is the excess moisture retention that many substrates produce. Stagnant water and lack of oxygenation causes premature aging and rotting of the roots , causing the plant to decline day after day. Against this, the mixture of substrates with inert components such as perlite make it less dependent on our way of watering.

And yes, it is quite common to water more than you should. Either due to an excess of unusual affection for our plants or because we anticipate that they may be experiencing excessive heat, we tend to water very frequently and in large quantities.

An extreme example is that of the Dracaena marginata plant , commonly grown indoors. It is usual to water once a week, so after a short time the upper part of the trunk, from where the leaves are born, shows a brown color that anticipates the rotting and complete defoliation of the plant.


Pearlite is considered an inert substrate that has mineral origins. The volcanic rocks that have been subjected to extremely high temperatures result of ignition undergo changes in their physical structure, swelling many times their original size and adapting a completely different texture and specific weight. After all, it is considered a glass, made up of mineral rocks such as silica , which makes up almost 75% of its total composition.

Perlite also contains other minerals such as sodium, potassium, aluminum, iron, magnesium, calcium, etc.

The expansion resulting from the heat of the perlite makes it a recommended material for waterproofing , with low weight and high drainage capacity. This causes the oxygen to be trapped between each of the granules of this substrate and evacuates the water very quickly.

Therefore, it is a highly recommended substrate for plants whose roots are not very friendly to excess water. We are talking about species of palm trees, cacti, bonsai and, in general, many indoor plants. The ideal of perlite is that it can be mixed in the quantities that we consider with nutritional substrates, such as peat , worm castings or compost. This achieves an ideal moisture retention, nutrient concentration and drainage ratio.


An ideal mixture for all types of plants, in general, is the 70% -30% or 80% -20% mixture between peat and perlite. Peat is the ideal substrate since it provides the nutritional base to the plant, takes temperature and develops activity of microorganisms. However, if we are not careful with watering , we can easily flood this substrate and cause root suffocation in our plants.

Hence, adding a porous and draining material such as perlite, helps that harmful excess moisture does not accumulate.

Substrates – Perlite Substrate 5L – Batlle

  • Pure components of the highest quality, used as substrate formers; ideal for making custom formulas at the user’s home
  • Perlite offers a pore size that provides easily assimilated water retention for maximum plant
  • In addition to providing aeration and sponginess to the environment
  • Package Weight: 1.3 kilograms
  • Power supply: AC


In this section we are going to discuss the main benefits of perlite, as well as some disadvantages that must be taken into account.


  • It greatly increases the drainage of water, so we increase the amount of oxygen in the environment and favors root development.
  • Being a porous material, it also has the capacity to store some water readily available to plants.
  • It weighs little, making it easy to transport. 100 L of perlite weighs approximately 12.5 kg.
  • Its white color means that the substrate does not overheat in summer, with high temperatures.
  • Improves the consistency of caked soils, typical of those containing many clays.
  • On a professional level, it allows to control all the nutrients that are contributed to the plant, since it is totally inert.
  • Its color means that it can be used at an ornamental level to cover floor surfaces in the garden or in flowerpots.


  • The white color is a disadvantage in winter, where it considerably reduces the temperature of the substrate and worsens root development.
  • Its high drainage of water, makes us have to increase the frequency of irrigation.
  • It does not provide any nutrients, so we must work like a hydroponic system if used alone. At a domestic and non-professional level, it is a disadvantage.

For us, the main disadvantage of using it alone is that it makes us more slaves to irrigation and the supply of nutrients. Therefore, except for cactus or bonsai species, where the akadama substrate can be used , we recommend mixing it with other components such as peat or coconut fiber .

Plants with low root development and dry substrate need good drainage, so they are mixed with materials such as perlite.


Trial, trial and error when preparing substrate mixtures is necessary, since not all plants have the same requirements. For this reason, most nurseries and plant multiplication specialists usually mix black peat with inert elements that increase porosity, and one of them is perlite.

For horticultural and ornamental planting, the best mix that has worked for us is 80% peat (any quality universal substrate) and 20% perlite , although other materials such as volcanic gravel, sand, expanded clay or vermiculite can also be used. .

If, for example, we deal with species that flee from humidity (Dracaena, cactus and crassulaceae, species with low root production, etc.), then the amount of perlite will have to be increased.

Optimal irrigation is one that allows 15-20% of the supplied water to drain, dragging salts that can be harmful to the plant and renewing the oxygen in the environment.

In a peat substrate with poor drainage, we can water abundantly, and the water, instead of coming out through the lower holes, comes out above the substrate, puddling everything in its path and taking several minutes to swallow that water. This substrate will generate 100% security problems for us.

A substrate that in less than 10 seconds of watering is already draining water, will also cause problems. There is no optimal use by the roots and all the water (with the fertilizer, if you have it), you will lose it completely and we will have to water every little time.

The ideal substrate, with a perlite mixture, is the one that once watered, after 30 seconds or more, gradually releases the excess water, preserving an ideal humidity when we feel it with the fingertip.

Wet feeling but without leaving water on our finger, that is the ideal moisture / substrate ratio.


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