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Starting Seeds Indoors

While things are frozen and white outside, some home gardeners are thinking about getting a head start on garden plants by starting seeds indoors. Rosie Lerner, Purdue University consumer horticulture specialist (recently retired), authored the publication, “Starting Seeds Indoors,” from which I’ll include excerpts in this article.

To do this successfully, you’ll need some growing equipment, an environmentally controlled space, seeds, growing media, and correct timing. While it’s not yet time to start most seeds indoors, some planning and procuring will be needed prior to trying this at home.

“Growing annual flowers and vegetables from seeds started indoors can be rewarding,” said Lerner. “Vigorous plants started indoors and then transplanted [outdoors] will flower sooner and produce an earlier harvest than those started directly outdoors.”

Good seed selection is the first step. “For best results, buy quality seed from a reliable dealer,” said Lerner. She said that some experienced gardeners may save their own seed from heirloom varieties, but this practice requires knowledge of proper techniques. She cautions not to save seeds from hybrid plants or easily cross-pollinated plants. It’s likely these plants would not remain true to the original and it’s also likely you would end up being disappointed with the results.

Several different types of containers can be used, including wood flats, fiber trays, plastic trays, clay and plastic pots, peat pots, or other containers. “Containers for starting seeds should be clean and sturdy and should fit into the space available for growing plants,” said Lerner.

Several types of growing media can be used, and they can be purchased as a ready-made mix or made from your own mix. Lerner said that the medium used for starting seeds should be loose, well-drained, and of fine texture. Some possible materials include vermiculite, peat, sand, milled sphagnum moss, perlite, or other materials. A percentage of loam garden soil can be used in mixes, but it should only be from one-third to two-fifths of the homemade mix, depending on other materials used and how “loamy” your garden soil is. A loam garden soil has a healthy mix of sand, silt, and clay that is conducive to plant growth.

Sterilization of soil and/or other media in the oven may be needed to prevent seedling diseases, such as damping off (see publication for more complete instructions). Care should be taken not to inadvertently introduce diseases to the growing media after sterilization, as these may actually spread more rapidly than they would have in unsterilized soil.

“The proper time for sowing seeds depends upon when plants may normally be moved outdoors,” said Lerner. “The periods range from 4 to 14 weeks, depending upon the speed with which seedlings grow and the conditions in the home.”

So, the timing of seeding usually works backward from the last expected spring frost, after which transplanting could occur. In Whitley County, the average date of the last 32-degree spring frost is around April 22-28. For an extra measure of safety, many like to count on Mother’s Day as the last possible frost. However, that is not always the case!

For example, tomatoes may take 7 weeks of growing time before being ready for transplanting. Cool-season vegetables may allow for earlier transplanting. Pansies and violets may require 14 weeks before transplanting, while petunias require about 10 weeks, and zinnias may only need 4 weeks.

While growing indoors, plants need quality light, proper temperature, timely watering, and perhaps fertilization. Special grow lights or fluorescent lights (1 cool with 1 warm white tube) can be used. Grow light technology has advanced much in the last decade.

Before transplanting plants in their permanent outdoor location, plants must be hardened off. This is about a 2-week process of gradually increasing the length of exposure time to the outdoors. Start with short periods each day in shaded locations away from the wind. Do not set outdoors on windy days or when temperatures are below 45 degrees.

For more information, access Lerner’s publication at the Purdue Education Store,

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