How to use perlite vs vermiculite in gardening

For years now I have been using both perlite and vermiculite in my potting mixes. In general, my guiding principle is to use perlite for aeration in my potting mix and vermiculite for water retention in my mix. While this general principle is true, there is a little more to understanding how to use perlite vs vermiculite in gardening.

Estimated reading time: 4 minutes

What is perlite?

Perlite is a non-renewable resource. Perlite forms from an uncrystallized product of rapidly cooling magma (volcanic glass). After being heated to temperatures of 850–900 °C (1,560–1,650 °F), the water contained within the substance evaporates and the substance expands 7-16 times. The expanded material then turns a bright white and is hard and porous. While perlite allows water and air to penetrate, it does not retain water.

Perlite is a soil additive that improves aeration and drainage in soils. When you purchase a potting mix and see white particles within the mix, that’s usually perlite. The following are some good uses of perlite:

• Improve aeration, drainage, and compaction in soils
• Cacti, non-cacti succulents, and epiphytes are good candidates for using perlite in the soil medium as they appreciate a drier medium
• Use to root cuttings from plants

What is vermiculite?

Vermiculite is also a non-renewable resource. It’s a mineral that is mined in several countries including the United States, Russia, China, South Africa, and Brazil. As is the case with perlite, vermiculite is heated to expand its particles. What’s interesting about vermiculite is that it can absorb up to 3 to 4 times its volume in water. Further, vermiculite attracts and holds nutrients such as potassium, calcium, and magnesium. These essential nutrients are then slowly released to plant roots. Vermiculite is usually brown in color and lightweight.

As with perlite, vermiculite is a soil additive. Use it for its moisture retention capability. Here are some good uses of vermiculite:

• Used in soilless growing mediums for its water retention and nutrient attraction properties
• Apply a thin layer on top of seed starting mixes to retain moisture and prevent crusting of the top layer of soil. Check out my article titled “The complete guide to starting seeds indoors”.
• Place a layer of vermiculite around bulbs when storing for winter. Vermiculite will absorb moisture and prevent mildew. I use vermiculite when I store my dahlia bulbs.
• Add to the soil of newly prepared garden beds, especially clay soil, to add air channels and retain moisture for plant roots. For more information on this topic, check out my article titled “How to prepare in-ground and raised garden beds”.

Perlite vs vermiculite, a summary

Perlite and vermiculite are used as soil additives, are non-organic, and are sterile. Both are lightweight. Further, both can improve drainage and soil aeration. Use perlite for plants that need a quick draining soil, where moisture retention is not critical, and where aeration is a goal (cactus are a good example). Use vermiculite when moisture retention is important and where you want to attract nutrients to the roots of the plant (especially good in seed starting mixes).

A word of caution

Both perlite and vermiculite are non-renewable resources and are thus not sustainable.

• Mining processes are not good for the environment
• The extreme heat needed to form these minerals into their final form relies upon fossil fuels which contribute to carbon in the greenhouse gases surrounding the planet
• Further, there is a carbon cost in transporting these materials

So, what are some alternatives? Consider using horticultural sand instead of perlite to improve drainage. Instead of using vermiculite for water retention, consider using coconut coir or compost.

Thanks for reading and I hope you now have a better understanding of how to use perlite vs vermiculite in gardening.

Here are some additional articles you may find helpful

• How gardening can diminish greenhouse gases
• Prepping garden beds for the season
• Creating and maintaining an organic vegetable garden – part one
• Creating and maintaining an organic vegetable garden – part two
• Four essential tools for working in your garden
• Survival of the fittest approach to thinning seedlings

References

• Virginia Tech
• National Gardening Association
• Horticultural Magazine
• Wikipedia – Perlite
• Wikipedia – Vermiculite