• Perlite is a volcanic rock that increases circulation and moisture retention in soil.
• There are different grades of coarseness perlite is available in, and they each have different uses and benefits.
• Perlite has many uses and benefits, including as a base for hydroponic gardening.

If you purchase seed-starting mix or potting soil, you may see small, white particles. That is perlite, a volcanic rock; it is commonly added to potting mixes to improve aeration, drainage, and water retention.

Learn more about perlite, when to add it to soil, and how it is used in hydroponics.

What Is Perlite?

Perlite is a naturally occurring volcanic rock mined in many countries including the western United States, China, Greece, and Japan. It forms as molten volcanic lava slowly cools and contains silicon dioxide, aluminum oxide, and other minerals. Once the perlite is brought out of the ground it is taken to processing plants where it is crushed into small pieces.

The form you find in potting soil or buy by the bag in garden centers has been superheated to 1600°F, causing the water molecules in the perlite to expand and pop into small light gray or white kernels.

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Types of Perlite

Perlite is sold for industrial, construction, and horticultural use. When purchasing perlite for gardening, it is important to select the correct form and grade. The most common grades used in horticulture are coarse, medium, and fine. Selection depends on the type of plants you are growing and the soil you are using.

• Coarse: Best suited for large potted plants, trees, and shrubs, add coarse-grade perlite to the soil for plants that are prone to root rot if overwatered.
• Medium: Medium-grade perlite is most often used in commercial potting soils. It’s a good addition to soil used for growing houseplants and container-grown flowers and vegetables. 
• Fine: Fine-grade perlite is included in seed starting mixes because the tiny particles will not impede the germination of seeds or the growth of fine roots. It’s also a good choice for potting seedlings because it helps prevent harm to the delicate roots of young plants. 

Why You Should Use Perlite When Gardening

If you want to use garden soil for houseplants or have heavy clay soil in the garden, adding perlite helps improve drainage. Perlite is sterile, lightweight, and doesn’t change the soil pH. It can be reused often as long as the soil is free from diseases or pests.

If you enjoy or want to start hydroponic gardening, perlite can be used as a growing medium. It is lightweight, inorganic, disease-resistant, and supplies iron, sodium, calcium, and other helpful trace elements to the water supply.

How to Use Perlite in Gardening

Perlite has many advantages in gardening. Here are just a few ways it can be used to help your plants.

Improve Soil Drainage

Adding perlite to soil helps prevent soil from forming clumps that impede water drainage. Proper drainage helps prevent root rot and fungal soil diseases. Perlite can be mixed directly into freshly tilled garden soil or added to potting soil mixes.

Moisture Retention

Popped perlite kernels have tiny pockets that can trap water and help the soil retain moisture while still draining well. Do note that it is a balancing act to add the correct amount of perlite per cubic foot of soil to get the optimum growing medium for individual plants.

Improve Air Circulation in Soil

Plant roots need oxygen to thrive. The shape and structure of perlite create pockets in the soil that improve air circulation and prevents compaction.

Create DIY Potting Mix

In a large container, add one gallon of sterilized garden soil sold at garden centers. Add one gallon of moist sphagnum peat moss and one gallon of perlite. Mix well to create a loose mixture for filling containers. Store in a covered container.

Create DIY Soilless Seed Starting Mix

In a large container, mix two gallons of peat moss and two gallons of fine-grade perlite. Store in a covered container and moisten the mixture well before adding to seed starting flats or pots.

Hydroponic Gardens

Perlite offers insulation against temperature fluctuations in hydroponic systems. One limitation of perlite is its neutral pH, which means it might not capture and hold nutrients as efficiently as other growing mediums.

What Are The Differences in Perlite and Vermiculite?

While both perlite and vermiculite help improve drainage in soil, they perform differently for moisture retention. Perlite holds some water in its crevices, while vermiculite absorbs water like a sponge. If you are looking for a product that will help maintain higher soil moisture levels, choose vermiculite to add to your growing medium.

Disadvantages of Perlite Use

Just as with any product, there can be issues when using perlite. Perlite is very lightweight and can float to the top of soil mixtures if it is not combined well. The dust from perlite, especially fine-grade particles, is considered nuisance dust and protection should be taken if you have respiratory issues. Always moisten perlite before mixing with other potting soil ingredients.