University of Illinois Extension


Barbara Larson
Unit Educator, Horticulture
Boone and Winnebago County Units

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Starting From Seed

Starting plants from seed is a rewarding project that gardeners should try at least once. Growing plants, especially annual flowers and vegetables, from seed is inexpensive, easy, and efficient. A much wider variety of plants and cultivars are available from seed than from ready to buy transplants.

Seeds may be planted directly in the garden or indoors in containers prior to transplanting outdoors. Plants with a long interval between planting and flower or fruit production, such as impatiens, broccoli, and tomatoes are usually started indoors. Plants with a short maturity interval or that transplant poorly, like radishes, peas, or sunflowers, should be sowed directly in the garden when soil and air temperature are right.

For optimum size transplants, planting dates for seeds indoors must be calculated rather than starting the seeds whenever convenient. Figuring the date to start seed takes a little arithmetic or, for the math impaired, counting weeks on the calendar.

Calculations are based on the average last spring frost date, which is April 25 in northern Illinois. Southern Wisconsin gardeners or Illinois gardeners in colder pockets should use May 5 as their average frost date. Cautious gardeners prefer to use May 5 so they have less worry about a late frost. The date the transplant should be moved outdoors relative to the frost free date should be figured. For example, tomatoes are damaged by frost and must be transplanted on or after the frost free date. In contrast, broccoli are very cold hardy and may be transplanted outside four weeks before the frost date.

Next the seed packet or catalog should be checked for the recommended sowing time and transplant time. Starting from the outdoor transplanting date, the gardener should count back the number of weeks the plant will need to germinate and grow to the proper size in order to get the seed sowing date. Tomatoes need five to eight weeks to germinate and grow to transplant size. By counting back or subtracting seven weeks from the last frost date of April 25, tomato seeds should be started around March 5. Gardeners who think late April is too early to put tomatoes outside, should push the seed sowing date back a couple of weeks to produce May transplants.

The materials needed to begin seeds indoors do not need to be expensive or elaborate. The minimum supplies required are: clean containers with drainage holes (pots, flats, peat pots, plastic cups or the bottom of milk cartons with holes punched in the bottom), clean potting soil or seed starting mix (do not use regular garden soil from outdoors), light (either natural or shop light with new cool white florescent bulbs), and water.

Seeds should be placed in pre-moistened potting soil at the depth listed on the seed package or at a depth of two times the diameter of the seed. Because most gardeners have difficulty thinning out extra plants, the seeds should be spaced an adequate distance apart to give the seedlings room to grow. Many gardeners cover the newly sown flats or pots with plastic until the seeds germinate so that moisture is maintained in the potting mix.

Most germinating seeds and young seedlings prefer air and soil temperatures of 65 to 75 degrees Fahrenheit. The temperature should be lowered 5 to 10 degrees after the first set of leaves appears. Reduced temperatures encourage shorter stockier plants.

Transplants may be successfully grown in the natural light of a south or west window, but most gardeners prefer using artificial light to supplement the natural light. Artificial light alone is also very effective. The key to using artificial light is to keep the light source within two to four inches of the top of the plant. As the plants grow, the lights should be raised to maintain the 2 to 4 inch space between the plants and light. Cool white fluorescent lights provide adequate light for seedlings and will not get too hot.

Seedlings should be watered at intervals to keep the potting mix evenly moist but not wet. Wet soil creates two problems: the cold inhibits germination and root growth, and dampness is a good medium for fungal disease development.
Fertilizer at quarter to half strength should be added to the water once a week after seedlings have true leaves. Complete fertilizers with nitrogen, phosphorus, and potassium should be used. Excess fertilizer will burn tender roots and promote weak spindly growth.

Gardeners with the winter blahs can get a jump start on the gardening season by starting a few plants from seed. Seeing the little plants push through the soil brings spring a little sooner.

February - March 2002: Starting From Seed | Can I Prune Now? | Lady Beetles "Housing" in Illinois| New Septic System Publications | Weird Weather

Past Issues

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