Many home gardeners get confused about when and why to use the soil amendments perlite and vermiculite. The color is different, but they look and feel the same.
As gardeners, we seek balance. We want well-draining soil with good aeration that retains moisture for the seeds, seedlings, and plants we grow.
Soil amendments help us achieve this balance.
And this balance is vital. Soil balance is critical for growing strong and healthy plants. And soil amendments like perlite and vermiculite help create soil ideal for any plant.
Quick facts: Use perlite for better aeration, drainage, and soil structure. Use vermiculite for drainage while retaining an even soil moisture level.
This article will briefly describe perlite and vermiculite. We will also list the advantages and disadvantages and explain how and when we use them.
Because even though perlite and vermiculite, in a way, are similar – they are different, and we use them differently.
What are perlite and vermiculite?
Perlite occurs naturally and is a lightweight, volcanic glass or rock. Gardeners use perlite as a soil amendment to improve aeration and drainage while helping to keep the soil from compacting over time.
Vermiculite is a naturally occurring mineral that expands into a lightweight, spongy material when heated. Gardeners use vermiculite for its unique combination of improving drainage while having a high water-holding capacity.
3 reasons for home gardeners to use perlite and vermiculite
As we have already stated, perlite and vermiculite are, in many ways, similar. They are lightweight, sterile, inert, easy to store, and can be mixed with all soil types. But they are not the same.
Here are the 3 main reasons we use them with examples.
1. Improved soil structure
The soil will compact over time. Adding perlite and vermiculite will help keep the soil from compacting and create better drainage and aeration for the plant’s root system.
We use perlite for all container and potted plants that need good drainage and in outdoor garden beds exposed to snow and rainfall. Here, vermiculite may retain too much moisture.
Vermiculite is, however, ideal for container-growing tomato plants and herbs like basil and chervil, where you want well-draining soil and an even level of soil moisture.
2. Retain moisture
Plants need water to grow but will not survive in constant wet. Like most things in gardening (and life), it is about balance.
Perlite will retain moisture but not to the same degree as vermiculite. This also makes vermiculite a perfect substrate for starting seeds where it is critical to avoid dry outs.
When starting seeds we cover the pot with a thin layer of vermiculite and spray to keep moist. As vermilulite is sterile and inert we prevent inviting diseases and unwanted nutrients.
3. Easy to use
Both perlite and vermiculite are easy to use, store and handle. But there is, of course, the dust factor.
- Handle gently, using slow movements
- Lightly water or mist before handling
- Work in a well-ventilated space
- If outdoors, make sure you have the wind in your back
- Use a facemask if sensitive to dust
Why do we use soil amendments like perlite and vermiculite?
For us, it comes down to maximizing plant health and saving money.
1. Maximizing plant health and yield
Healthy plants grow strong and produce a richer, more plentiful harvest.
We have plants that prefer evenly moist soil, like basil and tomatoes, and then there are plants like Mediterranean herbs and some hot peppers that like a mild dry-out between waterings.
So how can we cater to these different needs without buying expensive specialty soils for each particular need?
Easy. We use soil amendments to create the type of soil each plant needs.
- Better drainage and mild dry-out between waterings? Add perlite.
- Evenly moist soil with good drainage? Add vermiculite.
It does not have to be more complicated than that.
Buying in bulk keeps costs down. And we create our specialty soils for far less than buying commercial specialty gardening soils.
First, we buy good-quality gardening soil in bulk as a base for all our plants. We are often presented with 3 different qualities of soil and tend to go for the one in the middle.
Next, we buy perlite and vermiculite in bulk (100-liter sacks) and use them to create the individual soil types our plants need.
Buying in bulk and mixing our soil saves us a lot of money annually. And leftover perlite and vermiculite store well and can be used the following season.
Perlite and vermiculite, when using grow bags
We use homemade DIY grow bags for many plants, including tomatoes, peppers, horseradish, Mediterranean herbs, and lemongrass.
Grow bags are inexpensive to make at home, easy to move and can be made to fit your specific needs and requirements.
But as grow bags present the gardener with two challenges
- grow bags are made from a breathable material and can dry out quickly on hot summer days
- the soil in grow bags compacts over time, especially when we top water
Here we can use a combination of perlite to create an ideal growing environment.
For moisture-loving plants like tomatoes and basil, add 30% vermiculite for moisture retention and 10% perlite to avoid compact soil.
But for plants that prefer a mild dry out between waterings, add 30% perlite for drainage and soil aeration and 10% vermiculite for soil moisture.
Soil amendments like perlite and vermiculite put you in control and allow you to serve your plants’ individual needs better.