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I was always told that when starting seeds indoors that combining Vermiculite particles with the potting soil was crucial. What exactly is vermiculite, and what role does it play in growing seedlings? Just how “crucial” is it?

My first reaction is that seeds have been growing for ages without vermiculite, indoor and out, but since you asked we looked it up. According to the U.S. Environmental Protection Agency, vermiculite is “a naturally occurring mineral composed of shiny flakes, resembling mica. When heated to a high temperature, flakes of vermiculite expand as much as 8-30 times their original size. The expanded vermiculite is a light-weight, fire-resistant, and odorless material and has been used in numerous products, including insulation for attics and walls.” Vermiculite’s primary function in the garden is to act as a wedge that separates soil particles, increasing soil porosity and aeration by preventing soil from being packed too tightly. 
While some gardeners do choose to use this, know that some forms of vermiculite are created with asbestos, and therefore have health risks associated with using it. The U.S. Department of Public Health states that the health risk to home gardeners is low, due to infrequent contact with vermiculite. However, it is recommended to only use it in well-ventilated areas. Indoor gardening that uses vermiculite, therefore, might not be a safe choice.  Nevertheless, if you wish to use vermiculite, the U.S. Department of Public Health recommends taking a few simple precautions:
  • Use premixed potting soil. It normally contains more moisture and less vermiculite and reduces the amount of asbestos-laden dust.
  • Keep vermiculite moist while using to minimize dust and possible asbestos fibers in the air. As with any dust, breathing in large amounts of particles can cause nose and throat irritation.
  • Handle the material outdoors or in a well-ventilated area.
  • Avoid bringing dust into the house on clothing or shoes.
  • Try alternatives such as peat, sawdust, perlite or bark.
See our Gardening How-To Guide for all of your gardening questions, and remember to sign up for our gardening reminders too!
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  1. The trade name for this material is Syndanyo and was used very xieenstvely in the engineering business. Its useful because it is fireproof and makes an excellent insulator and can be machined and drilled where soft asbestos can not.When its use was banned the search for replacement was a failure, the most common being ceramic but this splits under extreme heat.The authorities turn a blind eye to its use in electric ovens and such as some products would be not possible.Its main danger is to the operators who cut it drill it etc.Its the dust that is dangerous.Touching it is not dangerous and you are ok.

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The Expert: Wendy Reinhardt Kapsak, MS, RDN, is the President and CEO of the Produce for Better Health (PBH) Foundation. At PBH, she guides the Foundation’s efforts to advance the overall effort of increasing fruit and vegetable consumption.
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