A guide to starting seedlings indoors

Originally published in the Kenosha News

By Horticulture Educator, Jeanne Hilinske-Christensen

At this time of year, gardeners and plant enthusiasts start dreaming about the upcoming growing season and contemplate starting seeds indoors.

There are many products on the market which aid in the process, from specially formulated seed-starting soil mixes to compressed soil pellets to dome-covered seed flats. Individual preference usually dictates what supplies are used.

If reusing plastic seed flats from previous years, it is advised to remove any leftover soil mix that may be stuck in the flat and disinfect with a bleach solution (9 parts water: 1 part bleach) prior to use. Use a well-drained seed starting mix that does not contain true soil. These lightweight mixes are sterile and free of weed seeds, and they provide the proper “soil” texture for germinating seeds.

Many types of annual flower seeds need to be started indoors in order for them to have ample time to grow and bloom during the upcoming growing season. For example, impatiens, geraniums and dusty miller should be sown indoors in early to mid-February. Start coleus, petunias and ageratum in March, and wait until April to sow celosia, marigold and nasturtium. Follow instructions on seed packets or in catalogs to judge the best time to sow other types of annual flowers.

Eggplant and pepper seeds can be started in March, but wait until April to sow tomato seeds indoors.

As the seeds germinate and the seedlings grow, they have a tendency to stretch toward light. Growing under lights will help decrease this tendency and prevent the seedlings from elongating and toppling over. Actual “grow” lights are available, at somewhat of an expensive cost, and provide certain ranges of light required for plant growth; however, two-tube standard fixtures with fluorescent bulbs work just as well.

If using supplemental lighting, be certain to keep the lights just above the tops of the seedlings, about 2 to 3 inches, and manually move the lights upward as the seedlings grow. Leave the lights on for 12 to 16 hours each day. Turn off at night to provide the dark cycle some plants require in order to properly develop.

While the seeds are germinating, keep the soil mix moist. A spray bottle on the mist setting can be used to water the seed flat before the sown seeds sprout, but once they germinate, try to water from the bottom to decrease the incidence of damping off, a common fungal disease encountered during indoor seed starting. Plastic covers (domes) can be put on seed flats to keep the soil moist but should be removed once the seedlings emerge.

A weak, water-soluble fertilizer mixed at one-quarter strength may be applied to seedlings once per week, if necessary.