Starting seeds

Irene Shonle, CSU Extension. Gilpin County.  As the light starts to come back at this time of year, and the seed catalogs flood your mailbox, many people’s green thumbs start to itch. Starting seeds indoors is a satisfying way to scratch that itch. An added bonus is that if you start your own plants from seeds, you’ll have a much wider choice of varieties to grow in your garden.

A word of caution on timing here – if you plant your seeds too early, they will become leggy and root bound before it is safe to plant them out in the garden. So think ahead about when you intend to plant them out in the garden, and then follow the suggested indoor start time on the seed packet (e.g., start indoors 6-8 weeks before planting outside).


Some of the earliest plants that can be transplanted out into the garden are members of the cabbage family – including broccoli, brussels sprouts, cabbage and cauliflower. They grow to transplant size in four to six weeks – so in the mountains you wouldn’t want to start them any earlier than the middle of March (and that’s only if you are going to protect them from spring frosts. Otherwise, start them a few weeks later.) If you are going to gamble on tomatoes, they need eight weeks inside, and should not be planted out before June 10 up here (unless you give them protection with something such as a Wall o’Water).


Many other cold tolerant plants like lettuce, kale and spinach are better sown directly in the garden rather than started indoors.

Seeds can be started in containers found around the house (plastic trays or cups, egg cartons, etc.) 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 and use a tray underneath to catch overflow.

Plant seeds for transplants in a homemade mix containing equal parts of sand, loam and peat moss, or purchase commercial potting or rooting mediums that are soil-less and sterile such as mixtures of perlite, vermiculite and organic materials. The mix needs to be well drained. Commercial mixes which have been sterilized are less susceptible to damping off (a fungal disease which kills seedlings). Commercial soil mixes are often very dry for shipping purposes and can be somewhat hydrophobic at first. It is easiest to mix the soil with water in a bowl before putting it into the seedling container.

After planting the seeds, water them in with a fine mist hand sprayer and cover lightly with a layer of plastic, or use a humidity dome. 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 like tomatoes or squash germinate better if soil temperatures are close to 80°F. After the seedlings emerge, remove the plastic and move the container closer to a bright window or light. Lower the temperatures to 55°F at night, 65-70°F during the day. Begin weekly applications of a soluble plant fertilizer.

Adequate light is critical for seedling health. Seedlings can be grown by a bright window, but turn them daily so they don’t lean towards the light. If a bright window location is unavailable, suspend a fluorescent light fixture three to four inches above the new plants, or there are clip-on or gooseneck lamps available for small numbers of seedlings. A combination of one cool white fluorescent tube and one warm white tube will provide the broad spectrum of light needed, or you can buy special full spectrum lights. For best growth, keep the lights on 12 to 16 hours daily.

The goal is to produce a stocky plant that will take off readily in the garden. Uniform watering and fertilizing, and at least 12 hours of sunlight daily will give the best chances. Good luck and have fun!

The CSU Gilpin County Extension Office is located at the Exhibit Barn, 230 Norton Drive, Black Hawk, CO 80422, 303-582-9106, Colorado State University Extension provides unbiased, research-based information about, horticulture, natural resources, and 4-H youth development. Colorado State University Extension is dedicated to serving all people on an equal and nondiscriminatory basis.

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