Starting Seeds Indoors
The main reason for starting seeds indoors is to get a jump on the growing season. It is also a helpful way to grow a greater selection of plants if you live in an area with a short growing season.
Using a sterile seed starting medium, sow the seed at the required depth carefully following the packet directions. A good rule of thumb is to sow the seed no deeper than twice its diameter. Some seeds need light to germinate and are best left on the surface of the growing medium, while others benefit from a gentle sifting of the medium over top (see packet for details).
Mist the seed-starting medium lightly or water from the bottom. Keep the medium surface moist, but do not overwater. For most seeds, average room temperatures of 20C (70F) is suitable for germination to occur.
Note: Wave Petunias enjoy a much warmer soil temperature of 30C (80 F) and must have their pelleted coating dissolved before germination will occur.
Once the seeds germinate, move the seedlings to a bright south- or west-facing window, if not using grow lights. To help prevent seedlings from reaching for the light and becoming weak or leggy, keep the lights on for 14-16 hours per day at a height of 15cm (6″) above the seedlings.
After seedlings produce their second set of leaves, they can be transplanted to larger containers. Fertilizing can also begin at this time and for every two weeks thereafter. Use a half-strength solution of 15-3-15 or 10-52-10 water-soluble fertilizer. Continue growing at cooler temperatures of 15C (65F) to produce stocky, healthy growth.