At first glance, it may seem perlite and vermiculite are very similar products and could be used interchangeably.
The fact is, they are quite different and impart very different qualities when used as soil amendments.
This article explores the differences between perlite and vermiculite and gives good advice to help you choose the right one for your gardening project.
Read on to learn more.
Both Vermiculite and Perlite Are Valuable Soil Additives
Both of these common garden products are inorganic, sterile soil additives.
When mixed in with potting soil or garden soil, they perform very different functions.
What Is Vermiculite?
Vermiculite is a lightweight material produced by the process of superheating mica.
It is a soft and spongy material capable of holding quite a bit of moisture through absorption.
Vermiculite can absorb three or four times its volume in water.
For this reason, vermiculite is a good soil amendment for plants preferring to be kept in moist soil.
This soil amendment will be light tan, medium brown, or dark brown.
Your product may be a mixture of these three colors.
The pH level of vermiculite is fairly neutral.
Vermiculite can be a good addition to a seed starting medium because it helps keep the soil evenly moist while protecting the seedlings against fungus.
What Is Perlite?
Perlite is produced by the process of superheating volcanic glass (obsidian).
It is a very lightweight, extremely porous, hard material.
Water is held briefly in the material’s porous surface.
The porosity also allows for greater air circulation. More on soil porosity…
For this reason, perlite is a good choice as a soil amendment for plants preferring dry, light, airy soil (e.g., succulents and cactus).
Perlite is always pure, bright white.
The pH level of perlite is slightly alkaline.
Perlite is rather delicate, and it will crush into dust between your fingertips.
This doesn’t cause problems when used as a soil amendment because when mixed into soil, it will not encounter much pressure.
How Do You Use Vermiculite and Perlite?
Both products provide soil aeration, but vermiculite can hold moisture for a longer period than perlite, so it is used differently in potting and the garden.
Vermiculite does very well with foliage plants which like moist soil and need a continuous release of nutrients.
As vermiculite holds onto water, it also holds onto the nutrients contained in water.
Using vermiculite in the soil helps keep it consistently hydrated and delivers added nutrients at a consistent, ongoing rate.
Because of its ability to keep the soil consistently moist, vermiculite is a great choice as an addition to a seed starting medium.
It is sometimes used on its own as a seed starter medium.
Perlite retains drops of water in the crevices and crannies found on its rough surface.
Having perlite in the soil can help increase the humidity above the soil and around the plants.
Perlite is a good choice as a medium for starting cuttings.
It is a good amendment for plants doing well in sharply draining soil.
Cactus, succulents, and epiphytes, such as orchids, appreciate the addition of perlite to their growing medium.
Which Is Better in the Garden, Perlite or Vermiculite?
While there’s a raging debate amongst gardeners as to which product is the best for outdoor gardening, you needn’t choose between the two altogether.
When deciding which product to use in your garden, you simply need to evaluate all of the factors of the specific situation.
You may use perlite in some instances and vermiculite and others.
Follow these guidelines:
Perlite is the best choice when:
- You’re dealing with plants that should dry out thoroughly between waterings.
- You are moving new seedlings from a tray to separate pots.
- The soil in your garden has heavy clay content.
Used in garden soil, perlite improves drainage and prevents problems with puddles forming on the soil’s surface.
Vermiculite is the best choice when:
- You are dealing with plants needing to have a consistent level of moisture in the soil.
- You are starting seeds in trays and want to protect the developing seedlings against drying out and against fungal infection.
Used in garden soil, vermiculite lightens the soil while improving its water retention qualities.
It also makes a good addition to large containers, and it works added to compost heaps and bins to help retain moisture.
Vermiculite is an excellent addition to the substrate used for growing mushrooms.
Additionally, it does well strewn across your lawn to help retain moisture.