I've been starting plants indoors for several years and I've found it's a great way to get a head start on the growing season. I can gain 4 to 8 weeks by setting out seedlings rather than planting seeds in my garden.
It's also a way to insure that I will have just the variety and color of the plants I need as well as any unusual or heirloom plants on my list.
Here are some tips to help you get started:
Soil - A key to success is using a loose, fertile, disease-free soil mix. I find the packaged potting soil easy to use.
Containers - You can start seeds in almost any container; it doesn't have to be fancy. I've used plastic flats, trays, clay pots, compressed peat pellets, and even a make-you-own-paper cup from recycled newspaper with a little gadget called an N. Viropotter. Cut-off milk cartons or plastic jugs, and egg cartons can also be used to start seeds. Last season's flats, trays, and pots should be cleaned and disinfected before use. Wash the containers in soapy water, and then disinfect them in a solution of one part chlorine bleach and nine parts water. Be sure to add holes in the bottom of the containers to allow for drainage.
Timing - Find out when your area is likely to have its last frost. You'll find this information in gardening books or check with your county cooperative extension service or local garden center.
Next, look on the back of the seed packet and find out how long it will take the seeds to sprout. Mark the last frost date on a calendar then count back the number of weeks needed for sprouting. That's the date to start the seeds. If you want the seedlings to be larger, start earlier. The time varies from plant to plant. Peppers require 7 to 8 weeks and tomatoes 5 or 6 to grow to transplanting size, while squash and cucumbers require only 2 to 3 weeks. Seedlings are ready to transplant when they have the first set of true leaves.
Seed Size - Usually smaller seeds require less soil to cover them than larger seeds. Check on the back of the seed packet for the proper seed depth. Seed size also determines the size of container and sowing method. Fine seeds, such as begonias and petunias, are typically sown in flats or trays.
After germination, the seedlings are transplanted into individual containers. Large seeds, such as marigolds and tomatoes, can also be germinated in flats. However, they are often sown directly into individual containers, thereby eliminating the need to transplant the seedlings before planting outside.
Temperature - Soil temperature is important. Cool soil retards germination. I use an electric grow mat under my trays to make sure the soil is around 75 degrees or so until seedlings have emerged. Provide an air temperature of 70 to 75 degrees during the day and night temperature of at least 60 to 65 degrees.
Water and Light - After seeding, water the soil gently until water drains out the bottom of the container. Just be careful not to wash seeds away. Place containers in plastic bags or cover the soil surface with plastic film until the first sign of the seeds' emergence. Then remove the plastic cover and be sure the container gets maximum exposure to light. Most seeds do not require light to germinate, but seedlings need full light exposure as soon as they emerge.