Growing Tomatoes from Seed
Sterile soil or soil-less mix is recommended for starting seeds indoors. Although you could start seeds in just about any soil, expert gardeners recommended caution. It's a bit risky to use regular soil from your garden. You'll minimize the chance of losing your seedlings to disease if you use only sterilized soil or soil-less mix for starting seeds.
Have you've seen a fuzzy white fungus on potting soil? If so it is probably damping-off disease--a term for the various fungi that can cause the seedling stems to rot away at the base. To help prevent damping-off, I'd really encourage you to use sterilized soil.
A lightweight sterilized soil mix like Jiffy-Mix (which is made from sphagnum peat moss and perlite) is ideal for starting seeds indoors. Why? Because it is not only sterile, but is free of weed seeds, and doesn't compact like regular soil. The problem with compacted soil is it can inhibit root growth of your seedlings.
You can make your own Peat-Lite mix by combining 50 percent vermiculite or perlite with 50 percent fine sphagnum peat. You could also stretch your budget by adding one-third sterilized soil to the mix.
Regular garden soil can be sterilized by heating. Take good, slightly moist garden soil and pasteurize it by spreading it on a pan and baking in the oven at 250 degrees. The soil should remain at 140 degrees for at least 30 minutes so having a thermometer is handy. It can be a bit smelly, but it works!
An alternative to growing seeds in a soil-less mix is to start your seeds in pre-formed peat pellets. It's a slightly more expensive alternative but very convenient. After soaking, the peat pellets expand into small soil containers that can later be planted directly into a pot or garden.
Or you can make your own soil blocks by investing in a soil blocking tool. This is a neat way to make your own two-inch soil blocks for growing tomatoes from seed. Use seed starting mix or potting soil to make the blocks.
Soil mixes for starting seeds are sold at most garden centers. For online sources two of the best for general gardening and seed starting supplies are Gardener's Supply Company and W. Atlee Burpee & Co.