For many home gardeners, starting seeds indoors is great fun. Successfully growing seedlings indoors requires high-quality seeds, a germination medium, containers, lights, and other supplies.
Flower and vegetable seeds can be purchased at local garden centers. They're also available from mail-order companies. A list of mail-order seed sources can be found in this article: What are some good sources of flower and vegetable seeds?
The germination medium should be lightweight, porous, and free of pathogens. Excellent seed-starting media are commercially prepared soilless mixes, such as Jiffy Mix. Use a high-quality, well-drained potting mix when transplanting seedlings into individual pots or cell packs.
Various containers can be used to germinate and grow transplants. Gardeners can purchase flats, trays, pots, compressed peat pellets, and other products. Previously used flats, trays, and pots should be cleaned and disinfected before use. Wash previously used containers in soapy water, and then disinfect them in a solution of one part chlorine bleach and nine parts water. Cut-off milk cartons, plastic jugs, paper cups, plastic food boxes, and other containers can also be used to start seeds. Holes should be punched in the bottom of milk cartons, jugs, paper cups, and similar containers to allow for drainage.
Uniform moisture levels are required for optimum seed germination. To maintain uniform moisture levels, place clear, plastic wrap over the containers. Flats can also be covered with clear, plastic domes.
While plants can be grown in sunny windows, they often become tall and spindly because of insufficient light. For best results, grow seedlings under fluorescent lights. Light stands are great, but are rather expensive. A standard fluorescent or LED light fixture is a much cheaper alternative. For best results, use full-spectrum light sources with a high output. The lights should be close to the growing seedlings, typically 4 to 6 inches above the seedlings. A timer can be used to turn the lights on and off.
A few other materials are also helpful. A rubber bulb sprinkler is a handy watering aid. The sprinkler produces a gentle spray that won't dislodge the seedlings or wash away the potting mix. Most seeds germinate best when the medium temperature is consistently 70° to 75°F. Placing containers in a warm location in the house, such as on top of a radiator or near a heat register, usually works fine. In cool environments, electric heating cables or mats can be used to insure warm medium temperatures.