Sowing Seeds Indoors
by David Robson
March 1, 2009

March is considered an ideal month to sow seeds indoors for starting your own transplants, said a University of Illinois Extension horticulture educator.

"Starting your own seeds holds several advantages over purchasing plants locally," said David Robson. "First, you can choose exactly what plants or cultivars to sow. You may desire a certain type or color unavailable locally.

"Sowing seeds is also an inexpensive means of obtaining a large quantity of plants. The cost of raising 100 marigolds is much less than buying them."

It's possible to get a jump on gardening by having plants ready when you want to transplant. Most plants are able to be set outside six to eight weeks after sowing.

However, Robson noted, all the advantages disappear if seeds aren't sown and maintained properly.

"Seeding success can be attributed to four factors: quality seeding medium, moisture, temperature and light," he said.

"Most homeowners use houseplant soil for starting seeds. Packaged mixes are satisfactory as long as the material is sterilized."

If the mix isn't sterilized or the package has been opened, sterilize the soil by placing the moistened soil in a metal pan for 30 minutes in a 200 degree Fahrenheit oven. An old meat thermometer should register between 130 and 140 degrees.

"Cooking soil smells, so you may want to place the soil in a roasting bag, or make sure the windows are open," he said.

Houseplant soil should be loose and well-drained. If it isn't, add peat moss, vermiculite or perlite. Garden soil is generally too heavy to use as an indoor seed medium unless it is modified with equal parts of peat moss and vermiculite.

"Some gardeners report success using individual peat pots for starting seeds," he said. "A common type is the Jiffy-7 pellet, which expands when wet."

Make sure you don't allow the pots to dry out. Likewise, avoid setting the Jiffy-7 pots in water.

Seeds need uniform moisture to germinate and grow. Part of the germination process involves absorbing water. It's important the water supply is present during the entire germination process.

"Too much water, however, can deplete the seeding medium of needed oxygen," he said. "Water only to maintain a moist soil, never soggy or saturated.

"Once seeds have germinated and are established, you might be able to reduce the amount of water needed. Do so carefully to avoid wilting the seedlings. Once wilted, most seedlings never recover."

It's a toss-up by professional horticulturists which is more important: temperature or light. Both are related and dependent on the other.

Soil temperature is crucial for seed germination. Ideal temperature is 75 degrees Fahrenheit. However, the air temperature for seeding should be 65 degrees.

Greenhouses can supply bottom heat by placing the seeding flats on steam pipes. Heating cables are available at most garden centers, greenhouses and nurseries to help with home germination.

"Setting the seed flat on top of the refrigerator can supply some of the bottom heat needed," he said. "However, the seeds can sometimes be forgotten.

"Once seeds have germinated, keep the air temperature on the cool side. In fact, lower temperatures usually produce a shorter, stockier and healthier transplant. Night temperatures can be as low as 55 degrees. Day temperatures should not be above 65 degrees."

Light is important for growth. Seedlings need at least 14 hours of bright light each day. Setting the plants in a south window helps, but temperatures may be too warm and produce vigorous but spindly growth.

"Plants can be placed under lights," Robson said. "Make sure plants are close enough to receive the maximum benefit, but far enough away to prevent burning.

"Plants should be placed no closer than six inches and no farther than 12 inches from fluorescent bulbs. For incandescent types, keep plants 12 inches away, but closer than 24 inches."

Tall, lanky seedlings with a large distance between sets of leaves indicate temperatures too warm or not enough light, he added.

Robson cautioned to avoid fertilizing transplants indoors unless growing conditions are ideal.

"It is better to wait until you transplant the seedlings outdoors," he said.

  • New Eden
  • Kids Garden
  • Plant a Row Grow a Row