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Science-based gardening information for Colorado communities from CSU Extension, Denver Botanic Gardens, and Green Industries of Colorado.

1034 – Starting Seeds Indoors   arrow

Starting seeds indoors is a simple and inexpensive way to enjoy many plant varieties not commonly found in garden centers.

What sorts of containers can I start seeds in?

Seeds can be started in containers found around the household – plastic trays or cups, egg cartons, and the like – or in seed starting trays or peat pots from the garden center. Regardless of what container is used be sure it has holes for drainage.

Are commercial seed mixes good?

A commercially available seed starting mix or fine textured potting mix will provide a sterile, weed-free medium in which to start the seeds.

How should I plant seeds?

Plant seeds according to package directions. It is generally recommended that most seeds be started four to eight weeks prior to the last killing frost.

How much water do seed mixes need?

After planting the seeds, water them in with a fine mist hand sprayer and cover lightly with a layer of plastic.

Do seed mixes need much sunlight?

Until the seeds germinate, keep them in a warm location away from bright sunlight. Most seeds prefer temperatures between 70-75°F to germinate. Seeds in the Solanaceae or nightshade family germinate better if soil temperatures are close to 80°F. As the seedlings emerge, remove the plastic and move the container closer to a bright window or light. For proper growth, seedlings require adequate light. If a bright window location is unavailable, suspend a fluorescent light fixture three to four inches above the new plants. A combination of one cool white fluorescent tube and one warm white tube will provide the broad spectrum of light needed. For best growth, keep the lights on 12 to 16 hours daily.

Should I fertilize seedlings?

After seedlings grow and develop true leaves, fertilize with a quarter-to half-strength water-soluble fertilizer to stimulate healthy, even growth. As soon as the seedlings are large enough to handle, carefully transplant seedlings into their own small pots to provide them room to grow.

What should I consider when I grow seedlings?

Take care not to expose seeds and seedlings to cold drafts, or allow them to wilt. Watch for signs of disease. Too much moisture, high temperatures and poor light weaken the plants and make them susceptible to the damping off fungus.

When should I start the hardening off process?

About two weeks before transplanting into the garden, start the hardening off process. For additional information on the hardening off process refer to message number 1802.

For frost dates, refer to: Climate Summaries with Frost Dates

For more information, see the following Colorado State University Extension fact sheet(s).

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