If you’re like me, you’ve probably been in this position before… You’re standing in the garden center trying to decide between perlite and vermiculite. All you can remember is that one looks like little Styrofoam balls. But the difference between perlite vs vermiculite is important to know for the prosperity of your garden. They seem very similar but differ in a few crucial ways.
Both are useful soil additives that provide distinct benefits around moisture, but they are assuredly not the same. Moisture retention in the soil is an important factor, of course, but you don’t want excess moisture retention. If you use the wrong one in your potting mix, you might make it too dry or too wet, and it’s important to be able to tell them apart.
Let’s get deep into perlite and vermiculite so that you will know which one you’ll want to use as a soil additive for your next batch of potting mix!
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What is Perlite?
Perlite is lightweight, easy to handle, clean, and has no odor. It has a pH of 6.6 to 7.5.
The life of a bag of perlite begins as volcanic glass — but not just any old glass. It’s formed when obsidian contacts water, creating a unique type of volcanic glass with high water content. When manufacturers apply heat to perlite, it puffs up into little white balls. Often they’ll mix these little white balls — what we call perlite — into potting soils to aid with soil aeration and drainage. It retains some water but also air on the surface of the little balls in all the hidden nooks and crannies.
Perlite is a good choice when plants in your garden require soil to dry out completely between watering. For example, if you’re growing a cactus or a succulent, perlite is a great addition to the soil.
Because it’s so porous, perlite does allow excess water to drain quickly…sometimes all over your porch. It tends to crush into a powder between your fingers easily, but this usually isn’t a problem because it doesn’t encounter that type of pressure in your pots or beds. Its chief use is to improve soil aeration, lightening the soil and giving better drainage and oxygen access for your plants’ roots.
Perlite has another very important use: it reduces soil compaction. Because it’s so light and airy, it tends to keep soils broken up more effectively. Now, this doesn’t make it the only soil additive to treat compacted soil, but it’s certainly one of the options you might use!
There is such a thing as too much perlite in the soil. Over time, perlite will stain to match the color of the soil it’s incorporated into, so you’ll need to watch for the distinctive shape of this mined volcanic rock in your potting mixes to ensure you don’t go overboard. An excess of perlite can reduce water retention in your soil.
What is Vermiculite?
Vermiculite interacts with potassium, calcium, and magnesium in your soil. It also helps to raise the pH slightly of your plants, even though it’s a neutral pH of 7.0.
Vermiculite is made from compressed dry flakes of a silicate material that is absorptive and spongy. The color of vermiculite is a golden brown to a dark brown, and it is sometimes difficult to tell from the potting soil it’s mixed with. When water is added to vermiculite, the flakes expand into a worm-like shape and act like an absorbing sponge. If you want to poke these “vermiculite worms” with your fingers, you’re not alone — that’s what I wanted to do when I first saw them too!
Vermiculite is best used for plants that require soil to stay damp and not dry out. For plants that love water, using vermiculite or mixing a healthy scoop into your potting soil is the way to go. It can absorb 3 to 4 times its volume when water is added, making your pots a bit heavy.
Since vermiculite acts like a sponge and absorbs more water than perlite, it doesn’t aerate the soil as well as perlite does. This means less oxygen for plant roots. If you use too much of it when growing plants that don’t need damp soil, you may create an environment where root rot or other fungally-caused plant diseases may develop. Treating root rot can be tricky, so it’s best to avoid it entirely.
Similarly, you might want to skip vermiculite if you’re adding things like coconut coir, peat moss, or worm castings (all of which are soil amendments that hold moisture). Be aware of your plants’ needs when you decide how water retentive you want your soil to be. Too much water retention can be as bad of a thing as too dry of a soil blend!
More Differences Between Vermiculite and Perlite
There are major differences between vermiculite and perlite, making it important to choose the right one, lest your garden is ruined by a bad potting soil choice.
We’ve already covered the biggest difference: Vermiculite will mix with soil and help to retain water. Perlite, on the other hand, will add drainage to the soil that it’s mixed with.
Vermiculite finds its way into many seed starting systems. It protects seedlings from fungus that often ruins seed starting and helps retain water in the cell trays that seeds start in. While perlite can be used with seedlings, it’s better when you move your seedlings into separate pots for additional drainage.
Another interesting point to note is that while soil moisture is crucial in a seed starting mix, it may not be as important in a regular potting mix. Comparing seed starting mix vs potting mix, you’ll often find vermiculite appears in a seed starting mix, but perlite’s only found in potting soil. This really depends on the age of a plant. Seeds need consistent moisture for germination, and young seedlings are very thirsty. A more mature plant has an established root system that’s able to seek out moisture through more soil, and thus a lighter soil it can easily penetrate with its root system is key.
Which To Use In Your Garden?
There’s a large discussion in the gardening community on which to use in the garden. Here’s the truth: it’s a false debate comparing perlite vs vermiculite. Both perlite and vermiculite have their own purposes in the garden.
Use Perlite If…
- You have plants that need to dry out before watering again.
- You’re blending soil for potted plants that needs to be well-drained
- You need to loosen clay soil or compacted soils in your garden.
- You’re starting cuttings — perlite can be a great temporary media for rooting!
- You want to lighten up a soil blend so it’s better aerated and less heavy.
- You garden in a damp climate where you need to promote soil drainage.
When added to clay soil, perlite can eliminate surface crusting and puddles. It will also help to reduce fluctuations in soil temperatures in your garden soil. Perlite will also improve both drainage and aeration in your home gardens. Horticultural perlite can be bought in different grades according to how you will use it. For general application, a fine to medium grade can be used. It’s free of weeds, disease-free, and sterile.
Use Vermiculite If…
- You need an additive for plants that need to be kept moist.
- You want your seed trays to develop strong seedlings
- You’re not using another moisture-holding material like peat moss, coconut coir, or worm castings
- You’re trying to keep the surface of a seedling tray damp (it works great on top when fully hydrated)
- You’re rooting cuttings (yes, vermiculite works well for short-term rooting too!)
- Your climate is dry, and your soil could use a little water retention booster.
Vermiculite is odorless and can be purchased in horticultural-grade bags with directions on working it into the garden soil. It’s a permanent soil conditioner and won’t break down in your soil as compost does. When it is watered, or it rains, the vermiculite will hold water in the soil until the soil begins to dry out and releases it. Vermiculite can be used in potted containers, on lawns, and for composting. It can be used in mycology for mushrooms added to the substrate. It can improve the soil that needs an additive to retain water for your plants that need it.
To summarize all of this information: Both perlite and vermiculite can be good as a soil amendment, but they’re used for different purposes. Both retain moisture, but vermiculite holds a lot more (which can become a risk for root rot or other fungal conditions in excess). Both have naturally occurring mineral origins, and vermiculite and perlite can be used to keep cuttings moist as they develop roots. Perlite is better for aerating soil and ensuring it drains properly.
In organic gardening, perlite and vermiculite both have their purposes. But we hope we’ve helped you to understand what the difference is between perlite vs vermiculite!
Frequently Asked Questions
Q: Which is better, vermiculite or perlite?
A: Neither one is “better” as they have two different purposes in the garden. There are even times when you might use both! One improves aeration, the other improves water retention.
Q: Can you substitute perlite for vermiculite?
A: We don’t recommend it. They provide different purposes. If you want a substitute for vermiculite, options include worm castings, peat moss, or coconut coir. To substitute perlite, consider rice hulls as an organic product that will gradually decay into the soil.
Q: What are the disadvantages of perlite?
A: Perlite has no nutritional benefit for plants. It’s a non-renewable mined material, so it will eventually become harder to acquire. It’s very lightweight and can actually blow away if on the soil’s surface, and it floats in water, so can easily be washed away if your garden floods. Finally, like many minerals, you should avoid breathing in the dust from it while working it into your garden so you don’t irritate your nasal passages or lungs.
Q: What are the disadvantages of vermiculite?
A: Vermiculite provides no nutritional benefits for plants. Like perlite, vermiculite is a non-renewable material, so isn’t permanently sustainable. It can hold a tremendous amount of moisture and create conditions where fungal root rots can develop. Bacteria and oomycetes (water molds) can also thrive in overly-wet soils, so it can cause the risk of plant damage from those sources as well.
Q: Can I use both vermiculite and perlite?
A: Well, you can, but there are very limited uses where most people would. Typically, you’ll want to use one or the other for their intended purposes. There is no harm in small quantities of one of these soil additives being blended into potting soil that holds the other, which is good for those of us who start seeds early and then transplant them into the garden!