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The Garden FAQ Index |

How do I start seed indoors?

Seeds started indoors usually germinate, but the
resulting seedlings are sometimes weak from lack of light
and perform poorly when placed in the garden. Gardeners
wanting only a few plants are probably better off purchasing
them from a local garden center.

Damping-off is a fungus disease common on seedlings
started at home. The disease causes seedling stems to
shrivel and turn brown at the soil line. Infected plants
fall over. At first, only a few fallen plants are seen then
more, until practically all the seedlings are dead. Damping
off is more of a problem on overwatered plants growing in
poorly drained soils.

Using pasteurized soil is another way gardeners avoid
diseases. Fill a pan or metal tray with a 4 inch, or less,
layer of moist soil. Bury a one and a half inch diameter
potato in the center of the soil, then cover the pan with
aluminum foil, and seal the edges. Punch a small hole in
the center of the aluminum foil and insert the bulb end of a
candy thermometer. Place the pan in an oven at 180 to 200
degrees. After the thermometer reads 180 degrees, leave the
soil in the oven 30 minutes then remove and allow it to
cool. The potato will be cooked if the soil is properly
pasteurized. Pasteurizing the soil is useless if dirty
containers are used. Pasteurizing soil in the oven can
create an odor some people find offensive. Clean clay pots
can be sterilized by baking while the soil is heated. Pots
can be sterilized by soaking them in a solution of one part
chlorine bleach and nine parts water. Rinse, and allow the
pots to dry thoroughly before filling them with soil.

An alternative is the purchase of new, plastic or
fiber, disposable trays or flats. Plants grown in peat pots
suffer little setback when transplanted into the garden.

Use a loose, well-drained, fine textured soil mix that
is low in nutrients. A suitable mix is equal parts of
pasteurized garden soil, sand and sphagnum peat moss.
Commercially prepared mixtures may also be used.

Fill the containers about two thirds full with soil.
Level the soil and soak it thoroughly. Sift more soil
mixture through window screening to form a layer that fills
one fourth to one half of the remaining depth of the
container.

Make a furrow one fourth of an inch deep in the sifted
soil. Sow large seeded plants directly into the bottom of
the furrow. Before sowing small seed, fill the furrow with
vermiculite, then sow small seed on the surface of the
vermiculite.

Sow seed in flats at the rate recommended on the seed
packet. Sow two to four seeds per peat pot if the seeds are
large. After planting, cover the furrows with a thin layer
of vermiculite, then mist with water. A fine mist prevents
washing the seed out of the soil. Some seed should not be
covered. To be sure, check the cultural suggestions for each
plant before sowing the seed.

Once seeds are planted, place a sheet of plastic over
the containers and provide temperatures between 70 and 75
degrees. The containers need no more water until the seed
germinates. Under no circumstances should plastic covered
containers be placed in direct sunlight.

Once seedlings are growing, remove the plastic and
provide proper growing conditions. Give the seedlings
adequate light. Even the sunniest windowsill provides
varying amounts of light and only from one direction.
Windowsills often lack adequate humidity and are too warm
for best seedling growth. Cool white fluorescent lights
placed three to six inches above the seedlings are a good
light source. The length of time the lights are on varies
with the type of annual grown. Some general guidelines are
given here, but read the seed packet for additional
information. A time clock will make sure the daylengths are
regular. If only one light fixture and time clock are
used, the plants must have compatible growth requirements.

These plants need 10 to 12 hour days and temperatures
between 60 and 65 degrees; calliopsis, china aster,
cornflower, gaillardia, petunia, phlox, poppy, rudbeckia,
salpiglossis, scabiosa, snapdragon, and verbena.

Most other plants need 18 hour days. On short days
they form flowers and never produce good flowering plants
outdoors. These plants are grown under 18 hour days at 65
degrees; cockscomb, cosmos, dahlia, marigold, morning glory,
scarlet sage, sunflower, and zinnia.

Annuals not included in the above groups are grown
under 18 to 20 hour days.

After removal of the plastic, the seedlings must be
watered frequently and fertilized. Water when the soil
surface begins to dry and use a house plant fertilizer
according to label directions.

Seedlings in flats should be transplanted to other
containers at wider spacings once two true leaves have
developed. Handle the seedlings very carefully as they are
easily injured. Use different flats but the same sterile
soil mix. Use a spacing of one and a half inches between
plants.

Starting seeds indoors is a simple way to enjoy many plant varieties not commonly found in garden centers. For optimal results, begin with a seed-starting tray filled with a sterile potting mix and a capillary or wicking mat underneath to water the seedlings from below. The best temperature for starting most seeds is 72 degrees F. during the day with a cooler nighttime temperature that doesn't drop below 65 F. Plant seeds, water, then cover them with plastic wrap until the seeds germinate. After germination, remove the plastic wrap. Suspend fluorescent lights three inches above the tray to provide light -- even if you have some natural light. As the seedlings grow, raise the light fixture to maintain the three-inch separation. When no supplemental natural light is available, add an incandescent bulb to produce better plant growth. For best growth, keep the lights on 12 to 16 hours daily.

After seedlings emerge and develop four leaves, fertilize with a quarter to half-strength water-soluble fertilizer to stimulate good, even growth. Transplant seedlings into their own pots to provide room to grow.

Credit for information from the following sources: Denver Botanic Gardens, MSU Extension Office, Colorado State University Cooperative Extension