What is perlite and what is it for?

Even if you have never bought perlite specifically, you have probably come across it. Its small fractions can often be seen in purchased soil, where it acts as a loosener. But, of course, its advantages do not end there.

What is perlite?

It is a natural material of volcanic origin, a rock. When lava comes to the surface, the areas where it comes into contact with the earth cool rapidly, forming obsidian (volcanic glass). Groundwater penetrating obsidian turns it into perlite.

Perlite is also called agroperlite – it is widely used in crop production. Its especially important qualities include moisture and air capacity, neutral pH, low thermal conductivity and unlimited shelf life. Agroperlite grains are completely destroyed in the soil in 3-4 years as a result of regular loosening.

Application of perlite in indoor and outdoor floriculture

Improving soil quality

  • In heavy soils, perlite prevents caking – when used with clay soil, it will provide air access to the root system and reduce the risk of rotting, crusting on the surface of the root ball.
  • In light sandy soils, perlite will help retain moisture longer due to its ability to absorb water and gradually release it into the environment.
  • The additive has a neutral pH, which means it can help reduce excessive acidity or alkaline reaction of the soil. In open areas, the use of perlite in the lowlands will prevent the spread of moss and moisture-loving weeds after floods and prolonged rainfall.

Seed propagation and cuttings

  • The practice of germination of seeds in perlite is popular. In this environment it goes without the typical problems – rotting, fungal diseases, algae or, on the contrary, lack of moisture. After the seedlings appear, they can be planted in the open air (unless you want to grow them in a greenhouse first).
  • In cuttings, perlite as an alternative to water also prevents rotting.
  • When growing seedlings in perlite it is necessary to water with an aqueous solution of fertilizer, because the material itself does not contain nutrients. Only complex fertilizers are used for this purpose, so as not to shift the pH of the medium from neutral to alkaline. As a rule, this method is used in industrial conditions, in addition involving special bacterial preparations for the formation of appropriate microflora.
  • Perlite is also used for even distribution of seeds on the surface of the ground: it is enough to mix them with perlite of a fine fraction. To protect against mold and substrate drying out, you can pour an additional layer on top – the material allows a certain percentage of sunlight, so even light-sensitive seeds will not suffer from such a solution.


  • In hydroponics, perlite is used as an independent substrate or its component, the coarse material is sometimes mixed with claydite to form the bottom drainage.


  • Together with water the material absorbs the fertilizers dissolved in it and provides a more even and natural flow of nutrients to the roots. In this way, the risk of chemical burn of the roots is minimized and the plants are more tolerant of fertilizers and the period between applications.
  • The low thermal conductivity of the material helps plants to tolerate rapid temperature changes. In the cold the soil with perlite cools more slowly, in the heat it heats up more slowly. Spring plantings and plants overwintering in such soil are less susceptible to frost (this does not negate the need to use a covering material).
  • Applying agroperlite before sowing lawn grass seed reduces the potential danger of flooding or drought.

Storage of planting material and crops

  • Bulbs, corms and tubers overwintering in perlite are better protected from rotting, temperature jumps, premature end of dormancy period. Planting material is poured over layers of perlite 2-7 cm thick, not allowing mutual contact.
  • Clean or fungicide-treated material will extend the shelf life of fruits and vegetables, prevent the development of mold and rot, and slow germination. Laying crops in perlite is done similarly to planting material – in layers, without touching. The thickness of perlite layers is up to 5 cm.

Air humidification

  • Moistened perlite of a coarse fraction is placed on trays around plants during drought or the heating season. Unlike spraying, this method gives a more gradual evaporation of moisture and a longer lasting effect.

What to replace perlite?

As a replacement for perlite as a leavening agent, vermiculite, brick crumbs, fine expanded clay, foam and sand are used.

Vermiculite dries out more slowly between waterings. At the same time, it is less prone to caking, does not create voids when backfilling, and has no abrasive effect on the roots.

Bricks and expanded clay have an alkaline reaction, so it is not recommended to use them for plants that require acidic soil. Claydite also reacts actively to ambient temperature – the substrate with it heats up faster in the heat and cools down in the cold.

Crushed foam and sand (not freshwater, but a coarser fraction) will also prevent caking, but the ability to store moisture and fertilizer and gradually give them to the roots they do not possess.

Minuses of perlite

  • In the material of white color it is quite difficult to see powdery and root worms, larvae of fungus midge.
  • Growing in pure perlite, a neutral pH can be a pain if you water hard: Over time, the pH of the substrate will become alkaline, negatively affecting plant development and making it harder for plants to get their nutrients.
  • Material is very dusty, it is recommended to use a respirator when working with large volumes.
  • Because of the positive electric charge, perlite is not capable of holding positive fertilizer ions – potassium, magnesium, ammonium and others.