White Balls in the Soil
Mon, Oct 25, 2021

White Balls in the Soil: What Are Perlite Used for in Potting Mixes

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White Balls in the Soil

Commercial potting soil is usually a mixture of several ingredients that together form an ideal growing environment for a wide variety of plants. And if any person can identify the soil without problems, even those far from gardening, then white balls in soil raise many questions even among experienced gardeners.

Soil Ingredients

Typically soil is made up of 3 main components: peat moss, aged compost or bark, and perlite (or vermiculite). The ratio of these components in your potting mix depends on the brand you purchase. But whatever you choose, all potting mixes have the same goal: retain moisture and provide good drainage, while leaving room for air. High-quality mixtures usually contain 10-15% white pellets in soil.

What Are the White Things in Potting Soil?

Many people mistakenly assume that these white stuff in soil are pieces of styrofoam. But really, it is nothing more than perlite beads.

What Is Perlite?

What Is Perlite

Perlite is a form of amorphous volcanic glass (SiO2) that has a relatively high water content, usually formed when obsidian is hydrated.

In the processed form it is used in horticulture in the form of a light, porous, granular material, consisting of silicon dioxide and oxides: aluminum, potassium, sodium, calcium, magnesium, and iron. All these natural minerals are part of the potting mix.

The rock is mined in open pits, after which it is crushed for subsequent heat treatment. High temperatures cause water to evaporate from the softened mineral, which causes it to expand 13-16 times its original volume.


In agriculture, these white squishy balls are used to mulch the soil. In gardening, it is a very sterile medium, a filler for mixtures. It is in these white specks that most weak-rooted plants are grown and rooted. The purpose of perlite is the same as that of sand, however, compared to sand, this white stuff in potting soil is lighter, more porous, and homogeneous. Crushed perlite is added to pot mixes, improving their porosity and drainage properties. Perlite is poor in nutrient chemical elements, completely devoid of organic matter.

Perlite Properties

Important properties that determine the effectiveness of tiny white balls in houseplant soil in floriculture are low specific gravity, environmental friendliness, high resistance to microorganisms and pests, and the ability to retain some moisture while maintaining aeration. These small white balls made of perlite perfectly increase the air permeability of the soil, providing oxygen to the roots of plants. Possesses insulating properties that protect root systems from extreme fluctuations in substrate temperature.

The porous structure of gray balls in the soil allows you to retain nutrients and a small amount of moisture, which for some time helps to avoid drying out of the roots in the absence of irrigation. The white pebbles in the soil also provide more even watering in the growing area and reduce the chance of overflow. However, compared to vermiculite, this material does not absorb water. Its task is to improve aeration and drainage.

Thus, it is a more suitable addition to the soil for plants that do not require frequent watering, for example, cacti, zamioculcas, succulents, etc.

An additional advantage of perlite used for plants is its sterility, which avoids the development of fungi that arise in an organic environment.

Benefits of Perlite

Benefits of Perlite in potting soil


It is known that 98% of all oxygen is supplied to the plant through the roots. Soils, closed to oxygen, lead to the fact that plants die of suffocation, the root system in such dense soils does not develop well. The introduction of expanded perlite into heavy soils makes the soils loose and breathable.


There should be plenty of water, but not too much. The soil should absorb water well and also give it well to the plant roots. At the same time, it would be good to spend it minimally and irrigate less often. It would also be very useful so that the water from the soil does not evaporate quickly so that the top layer does not form an impenetrable crust after drying.

These white clumps in soil are like reservoirs of water. When watering, perlite particles intensively absorb water and collect it up to 400% by weight. Even though perlite is very hydrophilic, it easily shares moisture with similar perlite particles. The layer of soil filled with perlite is evenly moistened. Only plant roots would get water from the perlite “reservoir”. The particles that have given up water to the root would immediately pull it up from other perlite granules, more full of water.

The top layer of the soil may dry out a little in the sun, but would not form a crust. Perlite draws moisture from the underlying layers, providing moisture to the upper roots.

White in color, highly reflective perlite in the upper layers can reflect the light and heat energy of the sun directly to the underside of the leaves and prevent the soil from overheating.

Stable Temperature Conditions

Good moisture migration in the soil, and therefore heat transfer in it, average the temperature in the root layer well. It is known that the thermal conductivity of the soil, and indeed of any material, directly depends on the density. The lower the density, the worse the energy moves through such an environment: the soil cools more slowly and heats up more slowly. This protects the roots from both freezing and overheating.


It is known that no matter how they are introduced into the soil, nutrients enter plants in the form of aqueous solutions directly through the roots. With the processes of water migration that take place in soil substrates filled with white perlite rocks, nutrients can certainly reach the consumer – the plant roots. Moreover, they may accumulate in the perlite particles.

No Weeds and Pests

The advantage of the natural component of soils, namely perlite, in the preparation of artificial soil substrates is undeniable. After all, perlite is obtained in ovens at very high temperatures, as a result of which they do not contain not only weed seeds, but also insect larvae.

Other Use

Pot with soil for growing

It is customary to use perlite not only in gardening. It is also a good insulation material in homes since after heating it becomes an effective insulating material with a low density. Often, perlite is also used as an aggregate in gypsum plaster or Portland cement. It is also an excellent filter material in water filtration systems.

Thus, perlite is a real salvation for the gardener. These white balls in the soil can work wonders for gardeners to grow a wide variety of plants. But before buying a potting mix, be sure to read the composition and make sure that it is perlite, and not other cheaper materials.

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