Starting seeds indoors

By Katie Drewitz, University of Minnesota Extension

The official start of spring will be here before we know it! 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, although full color spectrum LEDs are becoming more affordable. The light source should be movable so that it can be kept at about four inches 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. Look for seeds with disease resistance and consider days to harvest as we have a relatively short growing season in Minnesota.

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.

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.

Read and follow package instructions for how the seed needs to be planted. After sowing the seeds, bottom water the container or spray with a very fine mist. You may cover the container with a plastic dome or sheet of polyethylene plastic. Place pots or trays in a warm location with a constant temperature of 70-75 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. Remember that cool, moist environments can lead to fungal diseases such as damping off. If you use a plastic covering, 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.

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 to 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.

For more information on this or any other horticulture, agriculture or natural resources topic, reach out to your local extension educator. Minnesota residents in Fillmore and Houston counties can call 507-765-3896 (Fillmore) or 507-725-5807 (Houston) or email