![]() Using Perlite and Vermiculiteīoth products will improve drainage and prevent compaction although perlite is better for the later. Some bags may be labeled certified for organic agriculture, but all vermiculite is non-organic. They are however accepted in certified organic farming.Ĭlaims that “vermiculite can be organic, but it is not always organic” don’t make any sense. These nutrients are easily washed out in perlite, but held much longer in vermiculite due to its high CEC.īoth products are mined minerals and processed so they are neither natural or organic, as so frequently miss-stated. As the products are used and fertilized, both will hold nutrients in the soil water solution in and around the particles. ![]() Nutrients in Perlite and VermiculiteĪs un-fertilized products, perlite will release very few nutrients to plants, whereas vermiculite usually contains some potassium, magnesium and other cations in small amounts. If you are going to add either perlite or vermiculite, vermiculite will make a slightly wetter mix. The idea of adding vermiculite to media, be it peat moss, coir or bark, in order to make it wetter for plants is a myth. A peat + vermiculite mixture is drier for plants than just peat moss. Vermiculite does provide more water to plants than perlite, but not that much more, and it is certainly not as efficient as peat moss in this regard. Vermiculite absorbs more water than perlite (the water holding capacity), but it also holds on to it better keeping it away from plants. The difference between the water holding capacity and the wilting point is the amount of water available to plants, called the “plant available water.” This value is much more important to gardeners than the water holding capacity since it tells us how much water is available to plants, and this varies for different kinds of media. The soil still contains water, but plants start to die because they cant’ use it. In garden soil this is called the wilting point. ![]() The amount of water slowly decreases. At some point the peat moss will still contain water, but plants will no longer be able to use it. ![]() Over time plants absorb water and some is lost to evaporation. This is the water holding capacity of peat moss. For example, When a pot full of peat moss is submerged in water, allowing the peat to absorb as much water as possible and then allowed to drain, the amount of water in the pot will be around 76% of the pot volume. The above mentioned water holding capacity is a measure of how much water a media can hold. Vermiculite is a type of clay soil and does swell a bit as it absorbs water. Vermiculite will increase the water holding capacity of well drained sandy soil, but it won’t increase it in clay soil. In fact vermiculite makes peat slightly drier than peat moss alone. Based on the above numbers, that is not true. I see a lot of comments on line that say adding vermiculite to a peat-based soilless mix will make it wetter. These numbers are approximate and are affected by particle size as well as other properties. Mixtures of peat moss and either perlite or vermiculite result in a water holding capacity between these limits. The water holding capacity of peat moss, perlite and vermiculite are approximately 76%, 38% and 71% (v/v%). Properties of perlite and vermiculite Water Holding Capacity The mine producing this material has been closed for over 20 years and todays vermiculite is asbestos free. Some vermiculite was contaminated with asbestos a number of years ago and that led to the opinion that vermiculite contains asbestos. Vermiculite is light weight, chemically inert, holds a significant amount of water and nutrients, and adds some nutrients to soil. It looks similar to mica with thin layers of material. ![]() Vermiculite is mined silicate, a types of clay, that is heated to high temperatures to expand the layers in it to form the product used in horticulture. It absorbs water, has a low CEC (cation exchange capacity) so it does not hold nutrients very well, and it’s inert adding few nutrients to soil. Perlite starts as a mined volcanic glass-like rock that is heated to high temperatures to make it pop into the light weight material you are familiar with. I did a thorough review of perlite in a previous post called Perlite Myths – Should It Be Used in Gardens and Potted Plants? Perlite vs Vermiculite – Which Soil Additive is Better? ![]()
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