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Don Kinzler, Published February 14 2014

Growing Together: Scoffing at the Season: Banish winter by starting seeds indoors

Spring planting season has officially commenced! Watching seedlings grow on a sunny windowsill when it’s still frigid outside is a great way to give Old Man Winter a final finger poke in the eye.

Growing even a few of our own plants is fascinating and downright therapeutic.

Seeds can be started indoors now for homegrown transplants we’ll use in flowerbeds and vegetable gardens in May.

Dates to start seeds indoors are determined by the date you plan to “set them out” (garden talk for transplanting into flowerbeds and gardens). Each plant type requires a certain number of weeks to grow from seed into usable transplants. In our region, prime outdoor transplanting dates are between May 15 and 25. By counting backwards the necessary number of weeks, we can establish indoor seeding dates for each type.

  • Feb. 15-20 (12 growing weeks needed) – begonia, seed geraniums, celery.

  • March 1-5 (10 weeks) – impatiens, petunia, snapdragon, lobelia, dusty miller, ageratum, coleus, vinca, verbena, fountain grass.

  • March 15-20 (eight weeks) – alyssum, dahlia, dianthus, salvia, broccoli, cauliflower, cabbage, peppers, eggplant.

  • April 1-5 (six weeks) – cleome, celosia, marigold, nicotiana, statice, tomato, lettuce, oregano.

  • April 15-20 (four weeks) – Cosmos, calendula, nasturtium, four o’clock, zinnia, basil.

  • May 1 (two to three weeks) – squash, pumpkins, cucumbers, zucchini, watermelon, muskmelon.

    Materials needed

    Use soil-less seed starting mixes like Jiffy Mix, Miracle Gro Seeding Mix or one recommended by your local greenhouse.

    Containers should be about 2 inches deep, such as greenhouse trays, pie tins, egg cartons or any trays with bottom drain holes added. Use separate trays for each type because seeds grow at different rates. Also needed are wooden or plastic labels or stakes. We make our own by cutting plastic milk jugs into stakes 4 inches long and 1 inch wide.

    Why not seed directly into the final larger pots or cell-packs? Why seed into trays and then transplant? Because it’s easier to provide optimum germination conditions for a seed tray than a larger grouping of pots. Seedlings become stockier as you transplant them slightly deeper into the final container.


    1. Moisten the seeding mix the previous day by adding water to the bag and stirring by hand. Dry mixes can be difficult to water after seeding.

    2. Fill containers almost to the top with mix, then gently firm and level.

    3. Seeds may be broadcast over the surface of the mix or planted in rows. Being of German stock, I prefer neat rows. Press a ruler or pencil into the mix to make shallow furrows.

    4. Planting depth is important, and it’s usually shallower than we might expect. Small seeds like petunia can be merely pressed into the mix after sowing. Larger seeds can be sown into a furrow and covered with mix, or place the seeds on the surface and sprinkle mix over the top. As a rule of thumb sow seeds at a depth equal to two or three times the seed’s diameter. It’s better to err on the shallow side.

    5. Label with variety and date.

    6. Water gently after seeding with a fine mist or sprinkling can. Use warm water to wake up the mix and stimulate seed growth.

    7. Cover the container with plastic wrap or a clear lid to conserve warmth and humidity. If thoroughly moistened, seed trays usually don’t require watering until after seeds have sprouted.

    8. The most important ingredient for successful seed germination is warm soil between 70 and 80 degrees. Place seed trays on top of the refrigerator, next to the furnace, or by a heat register. Electric propagating mats are available for bottom heat. At this stage warmth is more important than light. If soil is too cool, germination is reduced or delayed. Window sills are poor because they’re warm during the day but cold at night.

    9. Peek at the seed tray twice each day. Most seeds take seven to 10 days to germinate. Larger seeds sprout quicker. As soon as seedlings emerge from the soil move the container to bright light. Remove the plastic covering.

    10. After germination, light is vital. Ordinary fluorescent shop lights work well. Locate seedlings two inches below the bulbs and provide 14 to 16 hours of light. If seedlings are grown in a bright sunny window rotate daily.

    11. Room temperature for “growing on” is best reduced to 65 or 70 degrees. Gently water as needed, but begin allowing mix to dry to encourage root depth.

    12. Seedlings respond greatly to half-strength water-soluble fertilizer applied once or twice a week in place of the regular watering.

    13. When seedlings have developed a pair of “true” leaves they are ready to transplant from the seed tray into individual cell-packs or pots for continued growing on.

    When the first seeds are planted, we’re officially on our way to spring.

    Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler’s Greenhouse in Fargo. Readers can reach him at forumgrowingtogether@hotmail.com