Yard and Garden: Starting Vegetable Plants

AMES, Iowa –Warm-season vegetables like tomatoes, peppers and eggplant are planted in the garden as small plants (transplants). This practice is becoming more common for cucumbers, squash, cantaloupes and watermelons, because transplants shorten the time by several weeks between planting and harvest. Horticulturists with Iowa State University Extension and Outreach provide answers to questions that will increase gardeners’ success with transplants. Contact Iowa State Hortline at hortline@iastate.edu or 515-294-3108 to have additional questions answered.

What are some good sources of flower and vegetable seeds? 

Flower and vegetable seeds can be purchased at local garden centers. They’re also available from mail-order companies. Mail-order sources include Park Seed, One Parkton Avenue, Greenwood, SC 29647 (www.parkseed.com); Stokes Seeds, P.O. Box 548, Buffalo, NY 14240 (www.stokeseeds.com); Harris Seeds, P.O. Box 24966, Rochester, NY 14624 (www.harrisseeds.com); Johnny’s Selected Seeds, 955 Benton Avenue, Winslow, ME 04901 (www.johnnyseeds.com); Seed Savers Exchange, 3094 North Winn Road, Decorah, IA 52101 (www.seedsavers.org); and many others. 

What type of germination medium should I use to start seedlings indoors? 

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. 

Which types of containers can be used to start seedlings indoors? 

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, 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 also can be used to start seeds. Punch holes in the bottom of milk cartons, jugs, paper cups and similar containers to allow for drainage. 

Can seedlings be grown in a sunny window or is artificial lighting necessary? 

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. A standard fluorescent shop fixture containing one 40-watt cool white and one 40-watt warm white tube works fine. The fluorescent lights should be no more than 4 to 6 inches above the seedlings. A timer can be used to turn the lights on and off. 

When should I sow my flower and vegetable seeds indoors? 

The growth rate of the seedlings and the outdoor planting date determine when to sow seeds indoors. The crop time (number of weeks from sowing to planting outdoors) for several popular flowers and vegetables are:

  • 10 to 12 weeks – Geranium
  • 8 to 10 weeks – Petunia, salvia and impatiens
  • 6 to 8 weeks – Marigold, pepper and eggplant
  • 5 to 7 weeks – Tomato, cabbage, broccoli, cauliflower and zinnia
  • 3 to 4 weeks – Cucumber, watermelon, muskmelon and squash