Starting Seeds Indoors

Growing annual flowers and vegetables from seeds started indoors can be rewarding. Vigorous plants started indoors and then transplanted will flower sooner and produce an earlier harvest than those started directly outdoors. Home gardeners can also grow cultivars which may not be available from local nurseries as transplants.  Starting seeds is pretty easy—all you need is seed, soil, containers, heat and light!

Start with a quality soil mix.  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, cell packs, pots, compressed peat pellets and other commercial products. Cut-off milk cartons or plastic jugs, paper cups and egg cartons also can be used to start seeds.

Previously used flats, trays and pots should be cleaned and disinfected before use. Wash the containers in soapy water, and disinfect them in a solution of one part chlorine bleach and nine parts water. Holes should be punched in the bottoms of milk cartons, jugs, paper cups and similar containers to allow for drainage.

Flower and vegetable seeds can be purchased at local garden centers and other retailers. They’re also available from mail-order/Internet companies. Store leftover seeds in the refrigerator. 

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 ensure warm medium temperatures.

A standard fluorescent shop fixture containing two 40-watt tubes provides sufficient light to grow seedlings indoors. For best results, place one cool white and one warm white tube in each fixture. Place the fluorescent lights no more than 4 to 6 inches above the seedlings. The lights should be on for 12 to 14 hours each day.

For more answers to your garden questions, contact your county ISU Extension and Outreach office.