COLUMBIA, Mo. – Seeds hold infinite potential for a seasoned gardener.

While it may be easier to transplant the tomatoes, peppers and cauliflower you bought from the local garden store, starting seeds indoors gives you the chance to jump-start your garden with perfect timing.

That begins with planting indoors in late February or early March.

“Starting from seeds lets gardeners pick varieties of plants that might not be readily available in yard and garden stores,” said David Trinklein, University of Missouri Extension state horticulturist. “Another advantage is that, with proper planning, one can grow a seedling that’s at the perfect stage of maturity for the least amount of shock when transplanted into the garden.”

To time seed sowing indoors, gardeners count backward from the date they want to plant outdoors. The time required to grow a properly sized transplant varies with species. You can usually find this information on seed packets and in gardening guides. Many use the frost-free date – when there’s a 50 percent likelihood that temperatures won’t drop below 28 degrees – as a guideline for when to plant outdoors. In Missouri, it ranges from April 5 in the Bootheel to April 20 in northern parts of the state.

The path from seed to transplant has a few stumbling blocks. The most common mistakes involve not providing enough light and improper temperatures.

“Plants really should have cooler nights and warmer days,” Trinklein said. “For warm-season plants like tomato, you need 63-65 degrees at night and cool-season plants like broccoli need 50-55 degrees. Failing to reduce night temperatures will produce a spindly, leggy transplant because the plant literally starves itself by using more resources than it makes.”

In general, most seeds germinate best at 78 degrees in front of a window with plenty of light. If there isn’t enough light, supplement with fluorescent bulbs or grow lamps. A spare room, garage or porch can provide nighttime temperatures comfortable for plants without chilling your family.

When starting seeds inside, ordinary garden soil won't do.

“A big difference with starting plants indoors is we don’t use soil, but rather a soilless medium that’s extremely porous, well-drained and contains no pathogens,” Trinklein said. “Such a medium is conducive to rapid seed germination and root growth if kept properly watered.”

Germination mediums contain a mix of peat moss and vermiculite or perlite that’s loose, well-drained, sterile and fine textured for optimal sprouting. A germination chamber can further be useful to coax seeds out of their shells. Because soilless mediums contain few if any nutrients, it’s important to fertilize a few days after seedlings sprout.

“Small transplants are very delicate and need tender care,” Trinklein said. “We recommend the first watering to include nutrient solution at half-strength from the recommendations you find on most soluble fertilizer.”

After seedlings put on their first true leaves beyond their initial cotyledons, you can transplant them into a more dense potting soil mix. While not necessary, this less-porous soil will hold more water than the medium used for germination, allowing less watering of the growing seedlings.

For growing the seedlings on, you can purchase kits from a local lawn and garden store or use small containers found around the home such as styrofoam cups. Whatever container you use, it’s important that it allows enough space for uninhibited root growth and provides adequate drainage.

“What we don’t want is to let seedlings become pot-bound,” Trinklein said. “We like plant growth to be unabated from the time you drop the seed until the time you first harvest, not stopping growth along the way.”

While the process can take a lot of attention to detail, it can be a fulfilling way to begin this year’s garden, he said.

“It’s a labor of love and there’s just satisfaction in having done it yourself.”

Read more in the MU Extension guide “Starting Plants Indoors From Seeds” (G6570), available as a free download at extension.missouri.edu/publications/g6570.

Writer: Roger Meissen