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Starting Seeds Indoors

University of Minnesota Extension, Stearns County News
February 19, 2014        
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. (02/19/14) — Although we still have weeks of winter left, we can start thinking about spring by starting seeds indoors.  Starting seeds indoors can help gardeners here in Minnesota get a jump start to assist them in getting the produce or strong appearance of flowering annual they want in the short growing season.  It is also a way for gardeners to save money by starting their own instead of purchasing.  Another advantage is that it allows gardeners to start varieties not readily available from local plant sources. 

Starting seeds indoors can be very successful with the proper preparation and steps.  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 to put together a set-up where a shop light with a 40-watt fluorescent 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.  Misting bottles may work best in some situations to not disturb the seeds before they germinate.  The growing medium is critical to provide the optimal growing conditions for the seed.  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, perlite, and peat moss can also be blended. Most importantly, using sterile mixture is critical to the health of the seedlings.  In part that also includes using sterile containers.  One option is to use a 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.  Peat pots or egg cartons also make good growing containers.  Ensure that the container is clean, sturdy, and will fit in the space available.

“Damping-off” is a fungal disease that can damage seedlings.  Signs of “damping-off” are wilting, or rotting of the stems.  Using sterile growing medium and sterile containers may assist in preventing this disease, however if these symptoms are noticed in the seedlings, remove them immediately to prevent from spreading.

Once you’ve cleaned the containers and have a good, sterile growing medium, fill the container full with moist growing medium, and then compress it using your hand or a flat surface so that it is about one-half inch below the rim.  Insert the seeds by either broadcast seeding or planting them in rows.  Sift a thin layer of planting medium on the surface.  A general rule of thumb is to plant the seed at a depth three times its diameter. Read the seed packet for specific instructions, for 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 degrees F. 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 and place the containers under bright lights.  Continue to water the containers so that the growing medium is moist, but not wet.  Once the plant emerges its second pair of leaves, transplant the seedlings into their own individual containers.  Begin fertilizing once the seedlings have several sets of true leaves using diluted fertilizer at quarter strength every week; water with plain water as required 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 Memorial Day in central Minnesota. Some plants such as the impatiens, geraniums, wax begonias, and pansies need to be started in February.  Seeds to start in March include broccoli, cabbage, cauliflower, petunias, snapdragons, and ageratum, as well as starting peppers in mid-March. Tomatoes can be started in the first week of April, along with amaranthus, bachelor buttons, and morning glory.  Mid-April is the time to start cosmos, sweet peas, and zinnias. 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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