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Perlite vs Vermiculite: Uses, Differences & How to Choose | Almanac.com

Perlite vs Vermiculite: Uses, Differences & How to Choose

Perlite and vermiculite in plant pots
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Learn all about the differences between perlite and vermiculite

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How do you know which is best to use in your garden—perlite or vermiculite? Some people think they are the same and used for similar purposes, but that’s not the whole story. Let’s look at the similarities and the differences and help you to pick the best one.

What is Perlite?

Perlite being added to a potting mix / Credit: RESTOCK Photos

Perlite is made from volcanic rock that has been heated until it pops, making it expand to many times its original size, like popcorn. You probably have seen the white pebbles in commercial potting soil and thought they looked like Styrofoam pieces. Some folks think they look like little pearls, which makes it easy to remember that the white stuff is perlite.

  • Perlite can hold a little water in the surface pockets, but its main purpose is to provide good drainage and aeration. If you have heavy garden soil that tends to compact, adding perlite will help make it more porous by providing channels for air and water to flow.
  • It is perfect for lightening up the soil for potted plants that need good drainage, such as succulents, cacti, and some orchids. It is also great for creating loose soil for rooting cuttings and starting seedlings. 
  • Since it is a sterile medium, it will prevent fungal diseases, such as damping off, from attacking newly germinated seedlings.
  • The only disadvantages to perlitle are that it is dusty, provides no nutrients, and is so lightweight it can float or blow away.

What is Vermiculite? 

Vermiculite is a mica-like mineral that expands when heated, similar to perlite. You probably have seen its shiny golden-tan chunks in commercial potting soil. It is very porous, and like a sponge, it can expand to absorb up to three or four times its weight in liquid, which it then slowly releases as needed. 

  • Vermiculite is ideal for moisture-loving plants. 
  • If your garden soil is sandy and dry, the addition of vermiculite will help it to retain more moisture.
  • Similar to perlite, vermiculite is a sterile medium that protects seedlings against damping off and other fungal diseases and is perfect for rooting cuttings.
  • It has the same disadvantages as perlite in terms of being dusty, but also can contain minute traces of asbestos so you need to be mindful when using it. Even though the EPA has determined that the danger to home gardeners is minimal, it advises us to wear dust masks, goggles, and gloves, and to use it in a well-ventilated area. Keeping it moist also helps to keep the dust from floating in the air.

Common Bonds

Even though vermiculite and perlite come from different minerals, they have many things in common:

  1. Often found in commercial potting mixes 
  2. Commonly used soil amendments
  3. Good for indoor plants 
  4. Have applications outdoors
  5. Can be used in hydroponics
  6. Lightweight
  7. Sterile
  8. Neutral pH
  9. Contain no nutrients
  10. Approved for use in organic gardens
  11. Made from mined substances that expand when heated

What to Choose?

The main difference between perlite and vermiculite is their ability to hold moisture. 

Use vermiculite if you are…

  • Potting up plants that crave moisture. 
  • Adding it to a bed with sandy soil or a hanging basket or windowbox -  anywhere the soil dries out too quickly. 
  • Using it for rooting cuttings to keep their tender new roots hydrated. 
  • Covering newly sown seeds to insulate them and keep them moist while they germinate

Use perlite if you are…

  • Trying to improve aeration. 
  • Potting up plants that need good drainage.
  • Rooting cuttings that may rot if kept too wet.
  • Lightening up a bed with heavy soil.
  • Trying to prevent or break up soil compaction.

There is no rule that says you can’t use vermiculite and perlite together. The perlite aids drainage and allows air to reach the plant’s roots, while the vermiculite provides a steady supply of moisture.
 

About The Author

Robin Sweetser

Robin has been a contributor to The Old Farmer’s Almanac and the All-Seasons Garden Guide for many years. Read More from Robin Sweetser

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