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soilless mixes

(Part 2) Perlite vs. Vermiculite: 6 Ingredients for Easy Soilless Mixes

The 6 Ingredients of a Soilless Mix, Part 2: Perlite vs. Vermiculite

Most soil mixes for a container plant contain little to no soil at all, which is why they are called soilless mixtures. They are usually comprised of a combination of organic matter, like peat moss, and inorganic material, like perlite or vermiculite. Indoor plants can thrive in actual soil from your backyard – just make sure you know what your plant needs and what type of soil you have!

Many of the ingredients for these soil mixes can be confusing for a first time DIY-er, so I’ve compiled a short list of the main components and how they differ. For this second installment, I compare the advantages and disadvantages of perlite and vermiculite so you can decide which is best for you and your plants.

soilless mix
ingredients for a soilless mix

Perlite vs. Vermiculite

Both soil additives change water retention and nutrient retention levels in your garden soil and in soilless mixes in different ways. Perlite – an amorphous volcanic glass – is usually formed by hydrating obsidian, a type of volcanic rock. This hydrated obsidian is then heated until the water molecules trapped inside the obsidian expand, exploding into tiny white pieces. In essence, this process is like popping popcorn!

Vermiculite – which is a hydrated magnesium aluminum silicate material similar to mica – is mined from the ground and then processed. The main factors in the formation are ascribed to natural weathering and percolating ground waters.

 

perlite & vermiculite
Perlite vs Vermiculite by Urban Turnip is licensed under CC BY 2.0

Despite seeming very similar on paper, these two soil additives have significant differences, so make sure you know what your plant needs before you choose perlite or vermiculite to add to your soilless mix! 

Associated Risks

There are some slight risks associated with both. Perlite is considered a “nuisance dust,” so be sure to take proper precautions. To avoid excessive inhalation, I always handle perlite outside. If you are working with a large amount, you may want to wear protective eyewear – like glasses or goggles – and gloves.

From 1919 to 1990, nearly 80% of the world’s vermiculite was supplied from one mine in Montana; however, it was discovered to have been contaminated with naturally occurring asbestos fibers. Once this was discovered, the mine was shut down. Vermiculite – now mined from all over the world – is regularly tested to ensure the product’s safety.

Perlite
  • White, fluffy, lightweight, and odorless
    • Looks like Styrofoam; however, Styrofoam is NOT a suitable substitute
  • Has a relatively neutral pH level ranging from 6.6 to 7.5
  • Advantages
    • Because perlite is porous, it allows excess water to drain quickly
      • Lix’s Pro Tip: I add perlite to heavier pre-made cactus and succulent mixes to ensure proper drainage!
    • Improves soil aeration, providing better oxygen access for the root system
    • Reduce garden soil temperature fluctuations
    • Loosens heavy, compacted garden soils, like clay soils
    • Does not decompose
  • Disadvantages
    • Contains no nutrients
Vermiculite
  • Golden-brown to dark brown, compressed, dry, odorless flakes that are absorptive and spongy
    • When vermiculite absorbs water, the flakes expand into a worm-like shape
  • Has a neutral pH level of 7
  • Advantages
    • Can absorb 3 to 4 times its volume in water
    • Vermiculite is a great additive to seed starters, as it keeps seeds from drying out during germination – aka the crucial time during the beginning of a seed’s growth
    • Protects plants from fungal diseases
    • Does not decompose
  • Disadvantages
    • Less porous than perlite, so vermiculite does not aerate the soil as well, leading to less oxygen for the root system
      • Be careful of overwatering, as your plant may end up suffering from root rot
      • Damp, wet soils are ideal environments for certain pests, like springtails and fungus gnat larvae – beware!
    • Contains no nutrients
In conclusion…
  • Use perlite if you want better drainage and aeration

  • Use vermiculite if you want better water retention

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