COLUMBIA, Mo. – Gardeners willing to put in a bit of effort can jump-start this year’s vegetable or flower garden by starting seeds indoors.

Tender seeds need the right amount of heat, light and water to germinate and thrive, says David Trinklein, horticulture specialist for University of Missouri Extension.

Accurate temperature control is important to help the immature plant emerge from its seed, Trinklein said. “That’s best done using a system that employs bottom heat.”

One way to apply bottom heat is to place electrical resistance cables under the germination trays to keep the germination medium at a constant 78 degrees Fahrenheit.

Light is also important. Some species need light for seed germination, and all species need light after germination.

“We don’t want those seedlings, once they do break out from under the germination medium, to be light-starved,” Trinklein said. “That causes what we call etiolated seedlings – very stretchy, leggy plants that will not thrive when transplanted.”

Sufficient water is required to help soften the hard seed coat and activate enzymes that trigger germination.

“The best way to hydrate the germination medium is from below,” Trinklein said. “Place the seed tray in a tray of tepidly warm water, let it imbibe as much water as it can, then let it drain and return it to the germination location.”

How long will it take seeds to germinate? It depends on the species.

“Cabbage, broccoli and cauliflower will take only a couple of days,” he said. “There are others, tomato and pepper, that might take five, seven or 10 days.”

How deep should you plant a seed? A common rule of thumb is to cover seeds three to five times their thickness, but Trinklein said that’s not always easy since most of us don’t have a micrometer to measure the width of tomato seeds. But don’t fret. Using a light, soilless germination medium makes seed depth less critical.

“Covering them too deeply is much less of a problem because it’s easy for these plants to push up through the light medium,” he said. “Of course, those species whose seeds require light to germinate should not be covered at all,” he added.

Germination is complete once the seedlings have fully emerged, meaning you don’t see any new plants coming up. Then it’s time to move seedlings to a growing-on container such as plastic bedding-plant cell packs. Then move the seedlings from the germination medium into a growing medium, sometimes simply called potting soil.

“Most commercially available growing media are mixtures of sphagnum peat moss, vermiculite and perlite,” Trinklein said. “The difference is the growing medium has a bit more peat moss and bit less vermiculite and perlite, allowing it to hold more water for the growing plants.”

That first watering after transplant should be half-strength nutrient solution, he said.

It may seem like a lot of work and a long list of requirements to germinate seeds indoors. Wouldn’t it be easier to wait and plant seeds directly into the garden later? Trinklein says there are many benefits to starting seeds early.

“You can pick varieties that might not be available in yard and garden stores,” Trinklein said. “Starting seeds early allows you to use the best-quality seeds, and you can control the timing.”

Related story: Germination 101

For more information, see the MU Extension publication “Starting Plants Indoors From Seeds” (G6570), available for free download at extension.missouri.edu/publications/g6570.