Hetty: Thanks for this timely and very good tip! Spring is arriving in most areas of North America (at least I hope everyone is finally warming up!) and what a great time for this tip to appear ... when folks are thinking about sowing and planting!
Years ago you could find vermiculite for sale in the garden department of all the big box stores but none of them in my area seem to carry it anymore so I purchase it at a local nursery who does stock it on occasion. I use straight moistened vermiculite as well as vermiculite combined with a little potting medium when I root cuttings, and as Dutchlady stated it works really well for starting seeds and seedlings! I've copied and pasted the following information from Wikipedia:
VERMICULITE:
Soilless growing media: exfoliated vermiculite is combined with other materials such as peat or composted pine bark compost to produce soilless growing media for the professional horticulturalist and for the home gardener. These mixes promote faster root growth and gives quick anchorage to young roots. The mixture helps retain air, plant food and moisture, releasing them as the plant requires them.
Seed germination: either used alone or mixed with soil or peat, vermiculite is used to germinate seeds. Very little watering is required. When vermiculite is used alone, seedlings should be fed with a weak fertilizer solution when the first true leaves appear. A tablespoon of soluble fertilizer per one imperial gallon (3.78 : 1) of water is the recommended mix.
Storing bulbs and root crops: pour vermiculite around bulbs placed in container. If clumps are dug, allow to dry for a few hours in the sun and then place in cartons or bushel baskets and cover with vermiculite. The absorptive power of vermiculite acts as a regulator that prevents mildew and moisture fluctuation during the storage period. It will not absorb moisture from the inside of stored tubers, but it does take up free water from the outside, preventing storage rot.
As a soil conditioner: Where the native soil is heavy or sticky, a gentle mixing of vermiculite up to one-half the volume of the soil is recommended. This creates air channels and allows the soil mix to breathe. Mixing vermiculite in flower and vegetable gardens or in potted plants will provide the necessary air to maintain vigorous plant growth. Where soils are sandy, mixing of vermiculite into the soil will allow the soil to hold water and air needed for growth.
PERLITE:
In horticulture, perlite can be used as a soil amendment, a medium for hydroponics or for starting cuttings. When used as an amendment it has high permeability / low water retention and helps prevent soil compaction.
