Home   News

Yard and Garden: Starting Seedlings

Feb 10, 2012

ISU Extension and Outreach horticulturists share information about starting flower and vegetable seedlings indoors. Learn how to avoid spindly, collapsed or yellow-green seedlings and minimize mold on peat pots. To have additional plant and garden questions answered, contact the ISU Hortline at 515-294-3108 or

The flower and vegetable plants that I start indoors get tall and spindly. Why?
Tall, spindly growth is a common problem when growing transplants indoors. Poor (insufficient) light, excessive watering, high temperatures, excessive fertilization and crowded conditions are factors that contribute to spindly growth.

Proper growing conditions should produce short, stocky transplants. Immediately after germination, move the seedlings to an area with a temperature of 60 to 70 F and place them under fluorescent lights (a sunny window usually doesn’t provide sufficient light). A standard fluorescent shop fixture containing two 40-watt tubes (one cool white and one warm white) works fine. Position the fluorescent lights no more than 4 to 6 inches above the seedlings. Leave the lights on for 12 to 14 hours a day. Thoroughly water the seedlings when the soil surface becomes dry to the touch. Fertilize every two weeks with a dilute fertilizer solution. Seedlings growing in flats should be transplanted into individual pots or cell packs when the first “true” leaves appear.

Some of the seedlings that I start indoors collapse and die shortly after germination. Why?

Damping-off is probably responsible for the collapse and death of your seedlings. Damping-off is caused by several different fungi. Environmental conditions associated with damping-off are poorly drained potting soil, overcrowding and excessive watering. Damping-off can be prevented by using clean containers, a sterile, well-drained potting mix, and by following good cultural practices. Wash previously used containers in soapy water, then disinfect by dipping them in a solution containing one part chlorine bleach and nine parts water. Sow seeds thinly to avoid overcrowding. Flower and vegetable seeds need an evenly moist potting mix for good germination. After germination, allow the potting soil to dry somewhat between waterings.

I’ve started flower and vegetable seedlings in peat pots. A whitish mold has recently appeared on the surface of the peat pots. Will the mold harm the seedlings?

The whitish or brown molds that grow on the surface of peat pots and other organic materials are unsightly, but will not harm healthy seedlings. However, the presence of molds may indicate excessive moisture levels. Overwatering may lead to damping-off and other serious problems. To avoid problems associated with overwatering, allow the potting soil to dry somewhat between waterings. Proper watering also will minimize the growth of molds on the surface of the peat pots.

The seedlings that I have started indoors are yellow-green in color. What should I do?
The yellow-green color is likely due to a nutrient deficiency. Nitrogen and phosphorus deficiencies sometimes occur when flower and vegetable seedlings are started indoors. Symptoms of a nitrogen deficiency include yellow-green foliage and stunted plant growth. Phosphorus-deficient plants have purplish leaves. Applying dilute fertilizer solution once every two weeks should help supply adequate nutrients to the seedlings.

Source: Iowa State University