Perhaps the best is organic compost. This is a mixture of organic material (composted manure, grass clippings, etc.) mixed with an equal amount of peat moss. This is usually mixed into the top 6 to 8 inches of the soil, and it should be added at least once every three years. Potting soil — This is usually a mix of sand and peat moss. It is used for growing vegetables in small containers, such as pots or trays.
I have read that the soil mix should be well-drained and loose.
This is what I use:
1/2 to 1 cup of composted manure 1 cup of vermiculite 1 cup of peat moss 4 cups of sand This is a pretty good mix, but if you don't have access to these materials, try making your own. I start my seeds indoors in a seed starting mix (usually a peat moss potting mix). I start them in a dark place and make sure they get at least 12 hours of light a day. After 3 weeks, I transplant them to my garden and let them grow for about 2 months before harvesting.