How to Use Soil Amendments-Vermiculite

Have you ever noticed how some potting mixes sparkle in the sun? That’s because they contain vermiculite, a soil amendment that helps with water retention, aeration and nutrient exchange. Vermiculite is a phyllosilicate mineral that is mined from rocks formed 1.5 to 3 billion years ago. Crude untreated vermiculite is used in a variety of industrial materials. The garden variety of vermiculite is called “exfoliated” vermiculite, which has been treated with extreme heat and pressure to force it to expand. This process creates a porous surface that is great for retaining moisture and nutrients. In the past, some vermiculites contained asbestos. However, those contaminated mines were shut down and modern vermiculite is rigorously tested to make sure it is free of this carcinogen. Vermiculite is a non-toxic mineral that will not deteriorate in your soil, so its effects last for a long time. Since it does not break down, it is not useful as a source of nutrients. Instead, it is a structural helper for your soil. Its unique shape traps water and nutrients, which can be extracted by plant roots as needed. This means you need to water less often than you would with soil that does not contain vermiculite.

What is the Benefit of Adding Vermiculite to the Soil

  • Improves water holding capacity of the soil.
  • Helps with aeration, although if this is your primary goal in using a soil additive, you should instead choose perlite.
  • Because it is a sterile medium, it is great for starting seeds and for propagating cuttings. Using plenty of vermiculite–or even straight vermiculite-can prevent bacterial and fungal problems such as damping off and root rot.
  • Improves drainage and lightens the soil in the garden, in raised beds, or in pots.

Using Vermiculite in the Garden and Landscape

  • Use 1/3 to 1/2 vermiculite in your potting soil for containers or when building your raised beds, or improve your garden soil by adding it in the spring with your other soil amendments and compost.
  • For new lawns, spread a 1/4 inch layer evenly around the planted area just after you seed it, then irrigate well. The vermiculite will help hold moisture near the seeds to improve germination.
  • Vermiculite can also be used for storing bulbs and root crops over winter. It will soak up any excess moisture from the air or the surface of the roots and bulbs, without desiccating the roots and bulbs themselves. Just layer the vermiculite and the roots or bulbs, and store in a cool, dry place away from sunlight.
  • Your worm bin can also benefit from the addition of vermiculite. Just add a handful to provide the grit your worms need to digest their food.
Vermiculite is used similarly to perlite, pumice, biochar and rice hulls. Each has its own pros and cons, and they can be used in combination to get the most benefits. Compared to these other soil amendments, vermiculite is best for areas and plants that require plenty of moisture, as it has the best water retention. It is not as good at aerating as perlite, so for heavy soils you should use perlite instead or in combination. Since it doesn’t break down like rice hulls, it is good if you want the benefits to last multiple seasons with a single application. Give your plants some vermiculite and grow organic for life!

2 comments

  • So, did you check the pH of the soil, peat moss can cause a decrease in your pH. You can add soil inoculants to boost your soil biology or add good compost or fertilizers with microbes. If the soil is really compact I would work in some compost, it will help with compaction and increase your soil biology. Another thing is to not walk in the areas that you are planting, keep defined paths and only walk on those to avoid compaction.

    Suzanne
  • Greetings. I recently began gardening (mostly veggies) in a community garden plot. A long, cold and wet spring prevented us from planting until fairly recently. During those cold/wet weeks in mid-late spring we added a couple inches of topsoil (scott’s premium sphagnum peat moss) and tilled it into the existing soil. Since then – In the past few weeks, we’ve planted numerous veggies and flowers. The weather over the past few weeks is great – not too hot, cold, dry or wet. The plants are living, but they’re definitely not thriving (at least not as well as some plants we’ve potted). It seems that the soil has become compacted – and when I dig into it I’m not seeing a lot of critter activity (no worms for instance). Given that all our veggies have been planted for 2-3 weeks, would it help/hurt to try to condition the soil – perhaps by amending the soil surrounding the plants with vermiculite, or by aerating the surrounding soil with spike shoes or even plugs? Thanks for your thoughts. Appreciate this article and wish I’d read it a couple months ago!

    SO

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