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Starting Seeds Indoors

University of Minnesota Extension, Stearns County News    
February 20, 2019                                    
Source:        Katie Winslow, Extension Educator-Horticulture, Small Farms and Local Foods 
University of Minnesota Extension 
Stearns, Benton & Morrison Counties

Starting Seeds Indoors
By Katie Winslow, University of Minnesota Extension 

ST. CLOUD, Minn. (02/20/2019) — The official start of Spring is about one month away. I do not know about you, but I am more than ready for some good Spring weather. While we wait you may consider starting a few seeds indoors. Starting garden flower and vegetable plants in the home can provide the home gardener with enjoyment as well as some definite advantages.  One of the greatest of these advantages is that it allows the gardener to start varieties of vegetable and flowers that are not readily available from local bedding plant sources.  In addition, it can save the gardener some money, particularly if large numbers of transplants are needed.

Before deciding to start seeds at home, it is necessary to look at the conditions necessary to grow healthy transplants.  To grow good transplants, you must be able to provide proper levels of light, temperature and humidity.  The greatest problem encountered is the lack of sufficient light.  Unless you are fortunate enough to own a greenhouse, you will need to use supplemental light.  The least expensive way to supply light is by using fluorescent lights.  An inexpensive shop light set-up with 40 watt cool white tubes will do nicely.   The light source should be movable so that it can be kept at about 4” above the seedlings and should be left on 12-14 hours per day.

It is wise to have a plan on what seeds you will be purchasing and planting to avoid impulse purchases later!  It is important to select good quality seed because the cost of seed is small in comparison to the investment of land, labor and time during the growing season. Look for seeds with disease resistance, and consider days to harvest as we have a relatively short growing season in Minnesota. Try something new each year, but grow your old standbys so you can make some performance comparisons.  

The starting medium should be loose, well-aerated, well-drained and sterile. Consider using one of the many soilless products available on the market.  These mixtures are sterile and drain well.   If you prefer to make your own starting medium, a good soil mixture can be prepared by using a 1-1-1 mixture of good garden loam, peat moss and builder’s sand.   To guard against fungus diseases like “damping off” and competition from weed seeds, the garden soil should be pasteurized.  

Select a container in which to start seedlings that is clean, sturdy, fits into the space available, and holds sufficient starting medium for good root development.   Pots, trays and flats from previous years can be reused if they are thoroughly cleaned and then sterilized with a solution of nine parts water and one part household bleach.

When planting the seeds, fill the container with the starting medium and then use a small block of wood or other flat surface to push the medium down so that it is about one-half inch below the rim.  Broadcast the seeds thinly on the surface or plant them in rows.  Cover the seed by sifting a layer of the planting medium, finely milled peat moss or vermiculite on the surface.  A rule of thumb is to cover the seeds to a depth of three times their diameter.  Some very small seeds, like petunias and impatiens, should not be covered at all, but pressed into the medium.  Read the instructions on the packet carefully, as some seeds have different requirements.

After sowing the seeds, bottom water the container or spray with a very fine mist.  Cover the container with a plastic dome or sheet of polyethylene plastic and place it in a warm location with a constant temperature of 60-75 degrees F.  Providing a consistent heat source from underneath can also be beneficial to seedlings.  Seeds will germinate sooner and produce healthier roots if the soil temperature is warm.  As soon as you see emerging plants, loosen the plastic cover and place the containers in bright light.  Keep the soil moist as the seedlings must not dry out, but use care so that the planting medium does not become waterlogged.  When the second pair of leaves appear, transplant the seedlings into peat pots or other individual containers.  Seedlings do not need fertilizer until they have several sets of true leaves. Fertilize with a diluted fertilizer solution only once a week. 

Do not start your seeds too early!  Best results are obtained when the transplants are relatively small, stocky plants that have five to seven leaves.  Refer to the seed packet for starting dates for vegetables and flowering annuals.  Recommended seeds to start in early March include broccoli, cabbage, cauliflower, petunias, snapdragons, and ageratum.  Peppers can be started in mid-March along with cleome, annual phlox, strawflower and sweet alyssum.  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. Early-mid-May is the time needed to harden off seedlings. 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 around Memorial Day in central Minnesota.