Like perlite, you can use vermiculite as a soil amendment when preparing for growing media. This material is mostly present in soilless potting mixes that are being sold commercially. But, it can also be used in soil-based mixes to improve structure and texture.
Vermiculite is a clay mineral that belongs to the mica family. The process of transforming this silicate material into lightweight particles is the same as perlite. Vermiculite is heated at the temperature of 1000°C (1832oF) until it fully expands and pops. The final product appears to have a white or yellowish, translucent, shiny, light-brown, or greenish color.
There are different grades of vermiculite that you’ll find in the market. One is a medium grade which is used for germinating seeds. The other is a coarse grade that is a good amendment for potting medium. Check out Vitax Vermiculite 10 Litres.
Advantages of Using Vermiculite
Improves Water Retention
Vermiculite has the capacity to expand once it absorbs water. Thus, it improves the water retention of the medium. The coarse grade has more capacity to hold water than the finer grade.
Provides Good Drainage
The coarse particles of vermiculite can add spaces within the medium. It alters the texture of the soil especially if it’s heavy on clay. Vermiculite reduces soil compaction.
Enhances Aeration and Root Penetration
Adding vermiculite to the soil will improve its structure. It will increase the medium’s aggregation creating hollow spaces where oxygen can fill in. This gives the root enough breathing room and freedom to penetrate further down the soil.
Improves Seed Germination Rate
Add vermiculite over the top of planted seeds in seed trays or pots and water it in. It maintains constant moisture which is an ideal condition for high germination rates of seeds. Its lightweight structure also makes it easy for seedlings to emerge from their seed casings.
Another good feature of vermiculite is that it’s very lightweight like perlite. It won’t make your medium heavy, unlike small pebbles or sand. You can make use of it as a replacement for heavy materials.
The process of producing vermiculite ensures that all pathogens are killed. The very high temperature where it’s subjected is sufficient to make the particles sterile.
High Cation Exchange Capacity (CEC)
Vermiculite has a high cation exchange capacity. Thus, it easily retains exchangeable ions such as magnesium, potassium, and calcium into its surface. It’s one advantage of vermiculite over perlite.
Mixing Vermiculite in the Potting Medium
Combine 1 part of garden soil (sterilised), 1 part compost, and 1 part of vermiculite (perlite or coarse sand can be used here as well)
Note: Different plants would require varying soil texture. Adjust the texture of the soil accordingly by adding more peat or coco coir, vermiculite, perlite, or coarse sand. Add in small portions until you achieve the desired looseness of the growing medium suited for your plant.
Soilless or Coco coir/Peat -based Mix
Combine 1 part of peat or coco coir and 1 part of vermiculite (or perlite). Add in small amounts of fertilizer. This will supply the needed nutrients for the plant.
For seedlings, combine 2 parts sieved compost; 2 parts sieved coco coir or peat; 1 part vermiculite (pre-wet)
Health Cautions in Using Vermiculite
Vermiculite is dusty and can aggravate respiratory problems when inhaled. Pre-wet the material before using it.
Some vermiculite is contaminated with asbestos which can endanger your lungs when inhaled. Use only the horticultural grade vermiculite for safety.