Several different methods work for starting seeds indoors; the one you select will depend largely on the space you have for starting them and how many transplants you want.
Start seeds in commercial potting mix. These mixes are usually sterile, containing no soil. They are composed of peat moss, composted bark, vermiculite, perlite, and other materials. Good mixes stay light and fluffy for the life of the seedling, holding lots of air and water and making a good medium for root growth.
Commercial Seed-Starting Kits
Perhaps the simplest method is to purchase a seed-starting kit. This usually includes a flat with a clear plastic cover and may include other aids, like planting mix and a heating cable or tray. Follow the instructions that come with the kit. Many nurseries carry these kits in the spring, or to find kits on line, search for “seed starting kits”.
Peat pots are plant containers made of compressed peat moss, about the size and shape of a small drinking glass. If you have a small garden, you can start seeds directly in the pots, and plant them in the soil without transferring them to another container or disturbing the roots. The pots are planted along with the plant.
Fill the pots with planting mix and put them in a flat. Plant three seeds in each pot, thinning to a single plant after it’s clear which seedling is the strongest. Avoid disturbing the roots of the seedlings you are keeping by snipping out the thinnings with a pair of scissors or your fingernails rather than by pulling them out. When it’s time to plant, tear off the rim of the peat pot, and plant the pot in the garden, covering it completely.
These compressed peat wafers are the planting medium as well as the pot. See Planting in Peat Pellets for instructions.
Other Individual Containers
Seedlings can be started in any containers that are about the right size (from 2 to 8 fluid ounces). People have used recycled plastic drinking glasses or coffee cups, leftover nursery 6-packs, tin cans, yogurt or cottage cheese containers, and a host of other things. Punch holes in the bottom and fill them with potting mix.
Planting in Flats
If you need a lot of transplants and don’t have a lot of space to grow them in, the best way to save space is by planting in flats. In the past, this was the most common way to start seedlings, and is still frequently used. Sow all the seeds very close together in one flat, or in a smaller container. When they have grown their first set of true leaves (second pair of leaves), transplant them to other flats, spaced about 2 inches apart. They only take up a lot of room for half the time they are indoors. Grow them in these flats until it’s time to plant them outside. For detailed instructions, see .
An innovative method for growing seedlings without containers is to plant in soil blocks. A hand tool is used to press potting mix into blocks about 2 inches square by three inches high. The blocks are held together by the peat moss fibers in the mix. Blocks are set in on a cookie sheet with 1/8 inch of space separating them to keep roots from growing from one block to another. For instructions see.