Growing Green

By Robin Trott, Extension Educator

As a flower farmer, I start tens of thousands of annual and perennial plants from seed each year. I can select varieties that meet the needs of my customers at a fraction of the cost of pre-grown plugs and liners. From Asclepias to Zinnia, my seeds are ordered and I am ready to start planting in January. If you’ve also selected the seeds to grow in your garden, you might be considering starting some of those plants indoors. Seed starting is a wonderful way to get a jump on the garden season, and can increase the varieties of plants you grow. It can also extend your growing season, making it possible to raise some long season varieties that usually don’t do well in Minnesota.

The last frost date in this area is about May 24 so plan to start your seeds so they are ready to transplant after this date. Many seeds need to be planted just four to six weeks before being moved outdoors. Others mature at a slower rate, and should be started 10 to 12 weeks before being transplanted. (Geraniums, pansies, wax begonias, dusty miller, impatiens, larkspur, lobelia, stocks, leeks, onions and celery need to be started in February.) Timing is important. If seedlings are too young, they will not be strong enough to survive outside. If they are too old, they will grow so big that they crowd each other and compete for light, water and nutrients.

Check the back of your seed packet for recommended starting times.

Select a sterile potting medium that is light and porous. Choose a soilless seed mix, or make your own with equal parts of peat moss, perlite and vermiculite. Wash and sterilize old pots with boiling water. Peat pots, egg cartons, plastic drinking cups and recyclables make good pots for starting seeds. I set my pots in solid plastic trays (plant flats) to minimize water spills. Fluorescent shop lights hanging on adjustable chains are perfect for seed starting. Place your seed flats under the lights, and lower the lights so they are no more than a couple of inches above the flats. Keep the lights on for 14-16 hours a day. As your seedlings grow, raise the lights so they are 2-4 inches above the tallest leaves. Keep your seedlings moist, but not wet, and fertilize weekly with ¼ strength all purpose fertilizer after several sets of true leaves appear.

Plants grown indoors must have a “hardening-off” period before transplanting. A couple of weeks before planting outside begin to take your seedlings outdoors for increasing longer periods. Start by placing them in a protected, shady spot in the warmest part of the afternoon. Bring them back inside in the evening. Gradually increase the amount of sun and the time spent outside. By the end of two weeks your seedlings can remain outside in a sunny area until you are ready to plant. If they are not gradually accustomed to the outdoor environment their leaves may be scorched by sun or wind; they may even wilt and die.

For more information about seed starting, visit: https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors

Until next time, happy gardening!