What is Perlite? What is Perlite made of?
Have you ever bought potted plants or veggie starts, and wondered what those tiny lumps of white are that look like bits of Styrofoam? That’s perlite, a non-toxic, lightweight soil additive that improves the soil structure to help keep plants healthy and happy.
It is a mined volcanic rock product, made from a type of volcanic glass that has been superheated until it expands and turns white. It is 70 to 75% silicon dioxide, but don’t expect it to provide that micronutrient to your plants because it breaks down extremely slowly.
What Does It Do For My Soil?
Its purpose as a soil amendment is not to provide nutrients, but instead to improve soil structure in two important ways.
- It provides excellent drainage. This soil amendment has a very porous surface that retains water and nutrients, but still allows excess water to drain away. This keeps your soil from becoming waterlogged, which in turn prevents root rot.
- It provides excellent aeration. 98% of the oxygen that a plant absorbs is taken up through the roots, so you can see why good soil aeration is important!
In the Garden
Horticultural perlite can be used everywhere, in any kind of soil. It is excellent both mixed in and sprinkled on top of propagation beds and seed starting containers.
- For seed starting, mix it half and half with Peaceful Valley soilless mix, Quickroot.
- For cuttings, use the same blend or as much as 100% perlite.
- In your garden beds, apply a 2" layer at the same time you apply compost and other soil amendments in the spring, and work it into the top 6 –12" of soil. One application will help keep your soil light and loose for several years.
- For container gardens, potted plants and raised beds, use up to 1/3 perlite per container. Succulents and orchids especially love perlite, and their potting soil can be mixed with half or even more perlite depending on the species.
- Perlite is also good for your lawn and promotes root growth. Broadcast it evenly across the whole lawn, where it will work its way into the soil over time. To help the the amendment get into the root zone quicker, spike or plug your lawn first.
- This soil amendment is also great for storing bulbs overwinter, to keep them fresh for planting in spring. Just alternate layers of fine perlite and bulbs, cover with more perlite, and store in a cool, dark, dry place.
Perlite vs. Vermiculite, Pumice vs. Perlite
There are many other soil amendments that and potting mixes have similar benefits to perlite, such as vermiculite, pumice, biochar, peat moss and rice hulls. Each have their own pros and cons, and ideal conditions for use. Perlite is the best choice where you want moderate water retention, excellent drainage and aeration, with long-term effects.
You can find more information on soil drainage here in our resource center.
It is also the preferred choice for seed starting and propagation in bulk quantities. You can even combine it with vermiculite or other soil amendments to get even better results!
Treat your soil to some perlite, and grow organic for life!