The choices you make when growing flowers or shrubs are one thing, but when it comes to plants that are going to end up on your dinner table, you might want to pay a little more attention to the materials you add to the soil.
Are you adding anything that will make the plants grow well, but that will also add contaminants or toxins to your food? What about perlite and vermiculite? They are often found in soil, and most people wonder just how safe they are.
Most won’t be able to tell them apart, but they are indeed two different compounds. And knowing whether perlite or vermiculite are safe in the vegetable garden is important to know before you start doing work with your soil.
What Is Perlite?
Between the two, perlite is the one most people recognize when they see it, and it’s the one material that causes the most distress. You know those little white balls or pellets you see in potting soil, that most people associate with styrofoam? That’s perlite. And it’s not plastic.
Perlite is a naturally occurring mineral that forms from volcanic obsidian in the right conditions. But the white material that you see in your potting soil is technically “expanded” perlite, which means it’s been heated to high temperatures until the water content inside vaporizes and the perlite itself expands. Think about what happens to a popcorn kernel when it is heated.
Once expanded, perlite is very light and porous, and excellent at adding air pockets to your soil. Now that you understand a bit better about what this is, the question still needs to be answered whether or not perlite is safe for vegetables?
We’ll get to that after looking at vermiculite.
What Is Vermiculite?
Vermiculite doesn’t stand out as brightly as perlite does, and you may not have even noticed it in your potting soil mix. It’s darker and blends in with the soil. It’s like perlite, as a natural mineral that has been heated up until it expands.
Similar to mica, vermiculite looks like little clusters of fine layers, sometimes described as “accordion shaped.”
Compared to perlite, vermiculite is the better choice if you are looking for a material that helps retain water as well as aerate. For aeration alone, stick with perlite.
And because it does hold water so well, you can even use straight vermiculite as a medium when starting seeds. It’s holds lots of water, and the light texture is ideal for those tender new vegetable seedlings.
Are Perlite and Vermiculite Safe for Growing Vegetables?
You may already be feeling better about both perlite and vermiculite now that you see they are both natural and rather inert materials. Are they safe for your vegetable garden? The answer is definitely yes. These materials are not going to add any possible toxins or residues to your soil that could effect your veggies (or any other plants for that matter).
Another safety issue is how these minerals will impact the environment when used outside. Is perlite or vermiculite going to be a hazard to anything else?
Thankfully, the answer to that is no. Both of these substances are not only safe for your vegetables, but also safe for anything else as well. Birds can easily tell what they can eat and what they can’t, and they won’t ingest either of these materials if they happen to start poking around your plants.
They are no different than any other small bits of stone.
Why Use Them in Your Garden?
The main reason anyone uses vermiculite or perlite in their soil is to improve drainage, add more aeration and to lighten up heavy or clay-based soils. All plants need a good supply of air for their roots, not just water.
Even if you are watering the appropriate amount, a lack of air pockets under the soil can still smother the plants and give the same symptoms as over-watering.
With an outdoor vegetable garden, it’s even more important to make sure you have well-draining soil because you can’t control when it rains, which can lead to over-watering no matter what you do.
They’re not the most common (or cost effective) options for large outdoor spaces, and are usually only used to loosen up soil for containers or houseplants. They both work nicely for indoor plants because they are light-weight to handle, fairly clean and compact to store.
Alternative Drainage Materials to Consider
For the purposes of breaking up heavy soil or improving aeration, vermiculite and perlite are only 2 options. There are a number of other materials that will also get the job done for you in the vegetable garden.
- Sphagnum moss
- Coconut fiber
- Shredded bark
- Wood chips (not sawdust)
- Fine gravel
- Straw or hay
Really, any natural material that is bulky and won’t break down immediately can be used for drainage. Perlite and vermiculite have the advantage of being inorganic (the same applies to sand and gravel as well), so they don’t decompose.
That also means these types of products won’t effect the pH or nutrient level in the soil. Moss or bark will eventually decompose and can lower the pH of your garden (make it more acidic).
Compost and manure can sometimes help with aeration in the vegetable garden, but they are more often used when you want to boost the nutrient levels in the soil.
When Does it Make Sense to Use Perlite or Vermiculite for Growing Vegetables?
Even though vermiculite and perlite are safe for vegetables, that doesn’t mean they are necessary for them. All plants need good drainage, but certain vegetables will do better with really loose and aerated soil.
Root vegetables like carrot, radish, potatoes, beets, onion and garlic will all need the additional drainage. Herbs are also known to like airy soil too.
As you can see, soil in a vegetable garden can be complicated. Hopefully you can relax a little, and use either perlite or vermiculite in your garden and not worry whether it’s safe or not.
Not only are they safe, they can be extremely helpful in keeping your plants healthy and productive.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.