How to grow flower and vegetable seeds indoors

Some types of vegetables and flowers are easier to grow from seed than others because they germinate quickly, emerge strongly, and don’t require as much indoor growing time. In the easiest category are marigold, zinnia, cleome, alyssum, cosmos, calendula, four o’clock, nasturtium, tomato, pepper, cabbage, cauliflower, broccoli, melons, cucumber and squash. Flowers that are slightly harder and take more weeks to develop include petunia, coleus, impatience, sage, and moss rose.

The general plan is to sow the seeds, germinate them, grow them in the seed box until they are large enough to handle, then transplant each plant into pots, cups or individual cell packs.

Why not plant the seeds directly in their final packages or pots? Why transplant small plants? Most seeds require specific temperatures to promote germination, and it is easier to give these ideal conditions to a small tray of seeds than to a larger assembly of pots or packs. Transplanting seedlings also gives vigor and creates more robust plants.

It is better not to start too early. The suggested sowing dates are as follows:

• March 1: impatiens, petunia, snapdragon and lobelia.
• March 15: alyssum, dianthus, salvia, broccoli, cabbage, pepper and eggplant.
• April 1: tomato, cleome, marigold and lettuce.
• April 15: cosmos, calendula, nasturtium, four o’clock and zinnia.
• May 1: squash, melons and cucumber.

The materials needed: Use a tagged seed mixture labeled as seed starter instead of all-purpose potting soil, as the seed starter mixture is ground more finely. Containers should be at least 2 inches deep with drilled or punched drainage holes. Clear plastic grocery or deli bakery trays work well and the holes are easy to add.

Transparent containers for baked goods or deli meats make great mini-greenhouses for starting seeds. Alyssa Goelzer / The Forum

Method:

1. Moisten the potting soil the day before use by adding water to the bag and mixing well. The dry mixture is difficult to moisten after sowing, and the seeds will often float to the surface.
2. Fill the container to the top with the mixture. It will settle down slightly when watered. Use a separate container for each type of seed, as different types germinate at different rates.
3. The seeds can be broadcast on the surface or planted in rows.
4. The planting depth is shallower than you might think. Small seeds the size of a poppy seed should be sprinkled over the surface without covering with the mixture. Cover larger seeds to a depth of about twice the diameter of the seed.
5. Label with the variety and the date.
6. Water gently with a fine mist or sprinkler-type watering can. Use lukewarm water to stimulate seed growth.
7. Cover the container with clear plastic wrap or a clear lid to retain moisture and heat. If watered well after sowing the seeds, trays usually do not require additional watering until the seeds have germinated.
8. Place the seed trays in a warm place to keep the mixture between 70 and 78 degrees. Electric sowing mats, available at garden centers, work wonders for seeds to germinate evenly and quickly.
9. Most types of seeds need seven to ten days to germinate. As soon as the seedlings are visible, move the container to a sunny window or under electric lights. To better eliminate the risk of newly sprouted seedlings stretching and becoming spindly, place the seed box in a bright light immediately after sowing.
10. When the majority of the seeds have germinated, remove the transparent lid from the container and remove it from the heating mat, if used.
11. If you are growing seedlings under fluorescent or LED lights, set a timer for 16 hours of light and eight hours of darkness.
12. The best temperatures for “growing up” are 65 to 70 degrees. Allow the surface of the mixture to dry between gentle waterings.
13. When the seedlings are just large enough to be handled easily, transplant them from the seed tray into individual cell packs or pots for continued growth.

When the seedlings are large enough to handle, transplant them into cell packs or pots. Alyssa Goelzer / The Forum

Don Kinzler, a longtime gardener, is the North Dakota State University Extension Horticulturist for Cass County. Readers can reach him at [email protected].