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Starting Seeds Indoors

University of Minnesota Extension, Stearns County News
February 10, 2016        
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns & Benton Counties

Starting Seeds Indoors
By Beth Berlin, University of Minnesota Extension
ST. CLOUD, Minn. (2/10/16) — Starting seeds indoors can help gardeners get the produce or annual flowers they want in our short growing season.  It is also a way for gardeners to save money by starting their own instead of purchasing transplants.  Another advantage is that it allows gardeners to start varieties not readily available from local plant sources.
The key to growing good transplants is having the proper light, temperature, and humidity.  Often the most common problem is inadequate lighting. Supplemental lighting is needed if you are starting seeds indoors.  An inexpensive lighting option is use shop lights with a 40-watt fluorescent that can be adjusted to different heights above the flat or container of seeds.  The light should be placed within two to four inches above the tallest seedlings.  If the lighting is placed too high the plant may become “leggy” as it reaches for the light.  Seedlings need to be placed under this direct light for 14-16 hours each day.  Timers may be used with the lights to provide consistency and ease for the gardener.
It is critical from the very beginning to provide adequate water to the seeds or seedlings.  The soil should be kept moist but not wet.  The starting medium must be loose, well-aerated, well-drained, and sterile.  Pre-mixed seed staring mixtures can be used or a soilless mixture consisting of equal parts of vermiculite, and peat moss can also be blended. Most importantly, using sterile mixture is critical to the health of the seedlings; that also includes using sterile containers. Wash containers with one-part bleach, nine-part water mixture to clean the trays, pots, or even recycled containers or cans.  Another option is to use boiling hot water to clean the containers. 
Once you’ve cleaned the containers and have a good, sterile growing medium, fill the container to one-half inch below the rim. Read the seed packet for specific instructions on planting depth; some seeds have different requirements. Once you’ve planted the seeds, water them in carefully.  Using a spray bottle will allow you to water with a fine mist without disrupting the growing medium or seeds.
Cover the containers using plastic domes or a sheet of polyethylene plastic.  The containers will now need to be placed in a warm location with a constant temperature of 60-75°F. Using a growing heat mat can help maintain consistent temperatures. Heat is critical to the success of the seeds’ germination; placing it in a window sill is typically not a good idea because it tends to be too inconsistent in temperature and can become too cool for germination.  As soon as germination occurs and you see emerging plants, loosen the plastic cover.  Continue to water the containers so that the growing medium is moist, but not wet.  Begin fertilizing once the seedlings have several sets of true leaves using diluted fertilizer at one-quarter strength every week; water with plain water as needed the rest of the week.
Timing is critical when starting seeds indoors; starting too early can lead to unhealthy, overgrown plants.  Ideally, transplants are relatively small and stocky plants that have five to seven leaves.  Best results are obtained by reading the seed packets for starting dates of both vegetables and flowering annuals.  The time needed to grow a transplant is usually given on the seed packet in weeks from the date to plant them outdoors, which for warm season plants is typically Memorial Day in central Minnesota.
Here is a list of common plants to start indoors:
• Early February: geraniums, wax begonias, and violas or pansies
• Mid-February: dusty miller, fountain grass, impatiens, larkspur, lobelia, and celery
• Early-March: ageratum, coleus, dahlia, petunias, rudbeckia, snapdragons, verbena, vinca/periwinkle, broccoli, cabbage, cauliflower, and head lettuce
• Mid-March: bells of Ireland, candytuft, cleome, dianthus/pinks, hollyhock, African marigold, ornamental pepper, annual phlox, salvia, sweet alyssum, peppers, and eggplant
• Early-April: amaranthus, aster, baby's breath, bachelor buttons, celosia, cornflower, four o'clock, French marigold , morning glory, nasturtium, ornamental basil and kale, and tomatoes
• Mid-April: cosmos, sweet peas, black-eyed susan vine, and zinnia
The seedlings also need a period of time in early to mid-May to “harden off.”  Hardening-off is the process where the transplants should be moved outdoors each day at an increasing increment until they are permanently moved outdoors.  This allows them to adjust to the fluctuating sun, wind, and temperatures of the outdoors.  If transplants are moved directly outdoors without the transition period they may undergo stress, sun-scorch, and not survive.
Starting seeds indoors can be an inexpensive way to get a wide variety of plants in your gardens.  Proper planning and set-up is important to having success when starting seeds indoors.  Visit the University of Minnesota Extension website at: and search “Starting Seeds Indoors” for more information.


Beth Berlin
Extension Educator, Horticulture
(320) 255-6169
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