Can you tell me what perlite is? Air for soil is what I call it, and it is the best substitute for compost when it comes to improving soil structure. Perlite can be used effectively in the garden if you know how to use it.
If you have ever bought potted plants, opened a bag of commercial potting soil, or purchased vegetable starters, you may have observed tiny white balls in the soil that look like small bits of Styrofoam.
Despite what some people may think, these white balls are actually soil components called perlite, not just fillers or artificial rocks.
What Is Perlite?
Here are a few things perlite isn’t: Perlite isn’t a type of soil; it’s an additive for soil that can also serve as a growing medium.
Neither plants nor soil benefit from perlite as a fertilizer or as an ingredient in microbial cultures. Soil structure must be kept loose and light for its benefits to be realized.
The defining characteristics of perlite are their inorganic nature, non-toxicity, and lightweight. However, if you’re an organic gardener, this shouldn’t dissuade you! (More on this below.) Perlite, also called expanded pyrite, is a mined volcanic rock that is utilized in many industrial building products for its structural stability, including masonry construction, loose-fill insulation, cement, and plaster.
Additionally, it’s used as a filter media for swimming pool filters, as well as a filter aid for beverages (such as juices, beer, and wine) and for waste water treatment.
The purpose of perlite is to provide drainage and aeration to the soil in the garden. I like to call it “air for the soil,” and it’s next best to compost in terms of circulating air between roots for strong, healthy plant growth.
If you look at perlite under a microscope, you will find that it is filled with tiny cavities that hold water (like a sponge), so it is efficient at delivering moisture to the roots. This provides perlite with the possibility of retaining up to four times its weight in water. It can also protect nutrients from washing away if it does not contain all those nooks and crannies.
However, the cavities in perlite mean that it is quite porous, so it drains excess water more readily than vermiculite and other potting media. It is important to keep soil from becoming waterlogged since this is the most effective way to prevent root rot and other fungal diseases.
How Is Perlite Made?
Perlite can be found in potting mixes and is sometimes called “volcanic popcorn” for good reason.
Perlite is a dense, amorphous volcanic glass with a high water content that comes directly from the earth. Perlite typically appears brown or black in its natural state because it forms through the cooling of lava when obsidian is formed.
As perlite is processed, it is rapidly heated to temperatures between 1560°F and 1650°F, which causes the material to soften and the moisture inside the glass to turn into steam. A trapped moisture in the material bubbles as it tries to escape, expanding the material up to 16 times its size, similar to popcorn popping.
As a result of the trapped bubbles, the expanded material appears white, and the resulting material has an extremely light, foamy texture that is chemically inert.
How To Use Perlite In The Garden?
The use of perlite in potting soil and soilless mixes is very common (especially in indoor seed starting), because it helps keep the soil loose and well-draining without allowing it to become compacted over time.
Perlite, vermiculite, and peat moss (or coco coir) can be combined for a clean, basic seed starting mix that works well for healthy seedling development and helps prevent disease transmission. You can use the mix to propagate plants, too. To root a cutting instead of just soaking it in water, place it in a small jar filled with moistened perlite.
Likewise, it is recommended that seeds be started in moistened perlite only, or that older seeds be tested in moistened perlite baggies. For in-ground or raised garden beds that have hard clay soil, in addition to using coffee filters for seed starting, you can also improve drainage by raking in 2 inches of perlite between 6 and 12 inches of the top layer of soil. During the process of amending the soil, you apply compost along with other fertilizers.
A single application of perlite can keep the planting bed light and loose for several years since it does not break down! This was my “secret ingredient” when I needed more than compost to break up hard dirt clods in our beds during my gardening years.
Additionally, some (but not all) bags of potting soil can be improved by adding more perlite.
In particular, deep-rooted plants are more productive when their roots don’t have to drive down into dense, compressed soil. Furthermore, perlite facilitates the drying process in the weeks or two leading up to harvesting. This versatile soil conditioner is always on hand in my garden, and I buy several bags every year because I can always figure out how to use it.
It’s important to know that smaller grades of perlite, as well as cheap perlite with little quality control, can be dusty (especially at the bottom of the bag). Perlite can be a dusty, abrasive material, so be sure to wear your dust mask and a pair of glasses when handling it.
Grades Or Sizes Of Perlite
Perlite is available in four coarseness levels or grades of granule size.
Super Coarse and Coarse Perlite
A dense, water-retentive soil (clay) or raised beds often contain this type of perlite to improve their water-holding capacity. Using size #4 perlite as a soil amendment is not recommended unless your soil is extremely heavy.
Medium Perlite
Commercial potting soils are mostly composed of medium-grade perlite. The potting media is a good size for window boxes, potted plants, and general use in the garden.
Fine Perlite
Small particles like these are great for starting seeds and rooting cuttings. Fine perlite is hard to come by in this size as a standalone product, so I usually use fine pumice, which is usually used for bonsai and succulent plants.
Benefits Of Using Perlite In The Garden
The following reasons make perlite an important part of gardening:
- No matter how heavy or saturated the soil is, it remains stable and functional.
- As it does not decompose, it is ideal for potting mixes for plants that are not repotted frequently (such as succulents and other houseplants).
- With a pH level of neutral, it is suitable for use in any container or garden bed.
- Perlite does not contain any toxic chemicals or additives; whenever you buy a bag labeled as perlite, that’s what you are getting.
- The material can absorb some water while letting the rest drain freely.
- Excellent aeration is provided by this device. Root development depends on good aeration since plants absorb almost all their oxygen through their roots. The soil food web is also supported by proper airflow, which is good for earthworms, beneficial nematodes, and other beneficial organisms.
- In addition to popularizing perlite as a growing medium for orchids, cacti, and succulents, perlite is also used in hydroponic setups to provide a drier environment for growing plants.
Does Perlite Cause Fluoride Burn In Plants?
The rumor is that perlite is responsible for fluoride burn in houseplants, the symptoms of which appear as brown spots or scorched leaves in plants like dracaena, spider plants, and Easter lilies.
Perlite is a mineral that is not found in most commercial potting soils; however, it has a very small chance of occurring.
The presence of fluorine toxicity can be caused by a number of factors, including fluoridated water, superphosphate fertilizers, low soil pH, and a number of other conditions which are independent of the perlite in potting soil.