How to Use Perlite to Improve Soil Structure

If you’ve bought potted plants or vegetable starters from a garden center, then you’ve probably wondered about those tiny white pellets in the potting soil. They look like bits of Styrofoam, but they’re not.

That’s perlite, a non-toxic, lightweight, mined volcanic rock. The pellets improve soil structure and each is about 70 to 75 percent silicon dioxide.

Perlite is a non-toxic, lightweight, mined volcanic rock.
Perlite, a non-toxic, lightweight, mined volcanic rock. (Photo: Maja Dumat/Flickr)

What does perlite do for my plants?

Perlite keeps plants healthy by improving soil drainage. The porous surface of the pellets holds water and nutrients but allows excess moisture to drain away.

The pellets likewise permit more air to flow through the soil. Plants draw almost all of their oxygen needs through their roots. Perlite helps ensure that the soil is sufficiently aerated for that purpose.

You can use perlite in any kind of soil. You can mix the pellets into the soil or sprinkle them on top of propagation beds and seed starting containers.

Perlite keeps plants healthy by improving soil drainage and airflow.
Perlite keeps plants healthy by improving soil drainage and airflow. (Photo: Huskita/Wikimedia Commons)

Should I use fine or coarse perlite?

Because coarse perlite has the highest air porosity, it offers excellent drainage and aeration. Coarse perlite is best for orchids, succulents, and container gardens.

The finer pellets are best suited for quality seed-starting mixes or root cuttings. You can also scatter fine perlite lightly across your lawn’s surface. Over time, the grains will work down into the soil to improve drainage. Good drainage encourages rapid root production.

Good drainage encourages rapid root production.
Good drainage encourages rapid root production. (Photo: Clivid/Flickr)

How to Use Perlite in Your Garden

For seed starting, combine one-part perlite, one-part vermiculite, and one-part peat moss or coco coir in a tub or bucket. Water the mixture down to keep it uniformly moist.

For your basic potting mix, use 1-part perlite and 1-part vermiculite for every 6 parts of peat moss. If you have leftover ingredients, you can save them for next season, or make a potting mix for your transplants.

For your basic potting mix, use 1-part perlite and 1-part vermiculite for every 6 parts of peat moss.
For your basic potting mix, use 1-part perlite and 1-part vermiculite for every 6 parts of peat moss.

In your garden beds, apply a 2-inch layer as you spread on compost and other soil amendments in the spring. Work it into the top 6 to 12 inches of soil. One application will help keep your soil light and loose for several years.

Perlite is also an excellent medium for storing bulbs over winter, keeping them fresh for planting in spring. Just set alternate layers of perlite and bulbs, cover with more perlite and store in a cool, dark, dry place.

Perlite is an excellent medium for storing bulbs over winter
Perlite is an excellent medium for storing bulbs over winter.

The Best Results

Many other soil amendments yield benefits similar to perlite. For instance, vermiculite, pumice, biochar, and rice hulls also help to aerate soils and ensure better drainage. Each has its ideal conditions for use.

Perlite is best when you want moderate water retention, excellent drainage, and aeration with long-term effects, says Meredith Cherry of Grow Organic. It is the preferred choice for seed starting and propagation.

More often, however, you get the best results from correct combinations of perlite, vermiculite, and other soil amendments.

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