If you are standing in the gardening center, trying to figure out which additive your soil needs the most, wondering what the difference is between perlite and vermiculite, then this article is for you. The two additives are similar, but they are distinctly different in a few important ways. Read on to learn more about these two all-natural soil amendments that gardeners use to change the water retention and nutrient retention levels in their garden soil.

What Is Perlite?

Perlite is made from volcanic rock, which is heated and crushed until it explodes in order to transform the rock into small white pieces. It has medium water retention ratings and low nutrient retention ratings. It is added to soil mixes in order to improve the drainage capability of both soil-based and soilless potting mixes.

Perlite helps insulate plant’s roots from extreme temperature fluxuations. It’s also used as a protective coating on pelleted seeds. Perlite is lightweight, odorless, clean, and easy to handle. It has a pH of 6.6 to 7.5. Add perlite to your soil for plants which need their soil to dry out between waterings, such as cacti or succulents.

• Perlite is great for seed starting mixes and blending your own custom potting soil mix
• Helps lighten and loosen heavy, compacted soils
• White granular pieces that contain about 6 percent water
• Perlite has a neutral pH level
• Holds nutrients and three to four times its weight in water
• Clean, sterile, odorless, and non-toxic
• Works as a lightweight sand substitute
• Won’t rot or mold
• Tends to float to the top of potted plant containers due to its light weight

What Is Vermiculite?

Vermiculite is magnesium-aluminum-iron silicate. It is an all-natural mineral product that is mined out of the ground and then processed into a soil additive that mainly increases water retention and nutrient retention levels in soil. It looks similar to mica with its layers or stacks, which are suited for trapping water. It has high water retention and high nutrient retention levels. Vermiculite’s water-holding capability makes it perfect as an anti-caking agent in dry pesticides and fertilizers.

Contrary to rumor, vermiculite does not contain asbestos and it is not a type of asbestos. This rumor is due to some vermiculite that happened to be contaminated with asbestos in a mine in Libby, Montana, which was closed in 1990 due to the contamination. Vermiculite from other sources has since been tested and proven to be asbestos free and harmless. The medium is considered safe for commercial and personal use.

Vermiculite is best used for water-loving plants that need their soil to stay moist at all times. Add a healthy scoop of vermiculite to the potting soil of plants that like lots of water.

• Great for seed starting or blending your own custom potting soil mix
• Helps to lighten and loosen heavy, compacted soil types
• Helps soil retain moisture and gives plants nutrients
• Mixes easily and well with soil
• Clean, sterile, non-toxic, and odorless

Vermiculite and Square Foot Gardening

Mel Bartholomew, author of Square Foot Gardening, describes vermiculite this way, “As you probably know it holds water yet drains when it’s filled, just like a sponge does. The plant roots grow around the particles and take in whatever moisture they need and since the particles of vermiculite take a long time to dry out, moisture is always there for the plant, enabling it to grow quicker and more healthy.” It is one of the three combined ingredients in his recommended soil recipe for the popular Square Foot Gardening method. The complete soil recipe consists of one third vermiculite, one third compost, and one third peat moss.

Mel has always been a big fan of vermiculite and thinks that it is far superior to perlite. He calls vermiculite, “the most marvelous natural material,” and says that even though perlite is much cheaper, he doesn’t mind paying up for vermiculite, particularly the coarser size of the material.

Common Traits of Perlite and Vermiculite

Perlite and vermiculite are both lightweight sand substitutes for soilless potting mixes which are often used to improve aeration and texture in potting soil and garden soil mixtures. Both are odorless, sterile, disease-free, insect-free, and seed-free. Neither medium will rot, deteriorate, or decompose.

Both mediums are used as an ingredient in soilless potting mixes that are made for the cultivation of plants as well as for seed germination, propagation, hydroponics, containers, and transplants. They are both also commonly used as carriers in dry fertilizers, pesticides, and herbicides to improve coverage.

Differences Between Perlite and Vermiculite

Both perlite and vermiculite are put to use in the garden to improve drainage, prevent compacted soil and increase moisture retention. They are both used in propagation of new plants and for seed starting and cultivation for indoor growing, outdoor growing, and composting. The differences in the way each medium retains water and how much water each medium can retain make them suitable for different applications.

Vermiculite is perfect for plants that enjoy lots of water, such as some irises and forget-me-nots. Perlite dries out too quickly for water-loving plants. The amount of water that vermiculite holds is too much for plants like cacti, succulents, or rhododendrons, which need a well-draining soil. Using vermiculite for plants like these could lead to root rot or death.