Vermiculite vs perlite: which is better for your potted plants?

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When it comes to vermiculite versus perlite, the names may hurt you in favor of the second candidate. Perlite, after all, comes from French for “pearl”, while vermiculite comes from Latin for considerably less attractive “breeding worms”.

However, perlite doesn’t really look like pearls, nor does vermiculite look like worms, and both amendments can improve soil porosity and water retention. While neither is perfect, they each have their pros and cons and have proven to be gems for gardeners around the world.

What is vermiculite?

Vermiculite is a “flaky” clay mineral – in more ways than one! When heated to around 570 degrees Fahrenheit, it opens up into light, tanned worm-like strands, so the “breeding worms” its name suggests. The size of the flakes makes different grades of vermiculite from micro to coarse. These spongy particles can aerate the soil and help it retain moisture.

Vermiculite lost some popularity when the product from a mine in Montana, which had been in operation since 1919, was found – after a 1999 EPA investigation – to be “contaminated with a toxic form of asbestos. ‘natural origin’. However, this mine had closed in 1990.

In 2000, the EPA reported that it had tested vermiculite products nationwide and concluded that “only 15 percent of these products contained enough asbestos for the EPA to quantify the percentage of asbestos reliably. Further analysis of the likelihood of asbestos dispersing in the air, during routine use of these products, indicated that this potential exposure poses a minimal risk to the health of consumers. The EPA, however, concluded that vermiculite could be dangerous for workers who come into frequent contact with it.

Related: The best seed starter mixes

What is perlite

What is perlite made of? You could say that it is natural “exploded” glass. This glass, which in its natural state can be of any color, is created by the rapid cooling of lava. When crushed and then heated to 1,800 to 3,200 degrees Fahrenheit, the steam trapped inside causes glass to swell into white pieces four to twenty times its original size.

The product obtained is light and porous. This makes it ideal for creating drainage channels in the potting mix without adding excess weight to that soil as sand sometimes does. Perlite is also available in fine to coarse grades.

The downsides of perlite include its fluorine content, which could be detrimental to plants sensitive to this chemical, including lilies, the prayer plant, and the spider plant. Although tests have shown that the fluorine in perlite seeps out quite quickly, it would probably be best to avoid using it in the soil of species sensitive to fluorine.

vermiculite vs perlite

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The biggest difference between vermiculite and perlite is moisture retention.

When making the decision between perlite and vermiculite, keep in mind that the differences between the two include the fact that vermiculite contains nutrients such as potassium, magnesium, and calcium that perlite does not have. not. Additionally, rounded perlite sometimes floats on the soil surface, making it less likely than flatter vermiculite to stay evenly distributed throughout the pot. However, vermiculite compacts more easily, which can reduce its aeration capacity. So, it would appear that it does not hold up as well as perlite.

The main difference between the two, however, is that while perlite for plants can suck four times its weight in water, vermiculite sponges up to sixteen times its weight in water. Thus, vermiculite is more efficient at collecting and redistributing moisture than perlite. Whether this is a benefit or not depends on the type of plants you are growing.

One thing the amendments have in common is that they generate a lot of dust. Therefore, if you do decide to mix your own potting soil, you will want to wear a dust mask or respirator while doing so.

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When to amend the soil with vermiculite:

What is vermiculite used for? Due to its water-holding abilities, vermiculite is typically used for seed starting, whether on its own or mixed with peat moss. Wet vermiculite can also be used to store seeds which will lose viability if they dry out. Vermiculite is often added to the soil of moisture-loving potted plants, such as ferns, primroses, and calla lilies, which, too, can die if left to dry out.

Gardeners who reside in already excessively humid climates should probably avoid incorporating vermiculite into the soil of outdoor pots, as it can hold too much water and cause their plants to rot. But gardeners in drought-prone areas might find vermiculite very beneficial, as the soil that contains it should hold moisture longer than that containing perlite. Those who often forget to water their houseplants should also opt for vermiculite over perlite.

vermiculite vs perlite

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When to amend the soil with perlite:

What is perlite used for? Its wet “pearls” are often used to root cuttings, as perlite is less likely to cause rot than vermiculite. Perlite is also a popular addition to potting soil for plants that require excellent drainage and not too much moisture, such as cacti and succulents, because soil containing perlite dries faster than soil containing vermiculite. Gardeners in humid climates may want to add perlite to the soil of their outdoor pots to help these containers flow more freely. And those who tend to overwater their houseplants may also find it beneficial in preventing rot.

While you can also add perlite or vermiculite to flower beds or raised gardens, you will likely find it more convenient and economical to use compost instead to improve soil aeration and water retention. in a large-scale cultivation area. This especially applies to non-raised beds since perlite can be sprayed by foot traffic, while vermiculite is likely to be compressed by it.

Related: What’s the Difference? Garden soil vs potting soil

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