Vermiculite is a sterile natural material. It is used in potting soil because it absorbs water keeping the soil moist as well as increasing spaces between soil particles enabling better root growth.Vermiculite is an ideal medium for germinating seeds as well as rooting cuttings because it is sterile and stays moist for a long time. Its water absorbing capacity makes it an ideal medium in which to store Dahlia tubers and other bulbs, that are routinely dug out of the garden in areas with severe winters.
Mix vermiculite into homemade potting soil. A good general mix consists of 1 part garden soil, 1 part vermiculite, 1 part bonemeal, 1 part lime and 1 part peat moss.
Mix seeds with wet vermiculite in a plastic bag. Place in a warm place such as the top of the fridge until they germinate. Use tweezers to pick up the seeds and repot them to continue growing.
Make a mixture of one half soil and one half vermiculite. Use this to root plant cuttings. Soak the mixture before planting the cuttings making sure not to compress it against the base of the cutting.
Store dahlia tubers, over winter, in a plastic bag filled with vermiculite. Keep the bag open to facilitate air movement. Punching holes into the bag will also help the bag to breathe. Store the bag in your heated shed or garage.
Health Canada says that although most processed vermiculite is safe some vermiculite ore, used in processing, may contain trace amounts of asbestos. Asbestos can lead to lung cancer. Health Canada recommends keeping pure vermiculite damp to avoid dust and to use pure vermiculite outdoors.