Timing is Everything

Seed packets and seed catalogs generally include information on whether the seeds can be started indoors as well as seed spacing, planting depth, days to germination (sprouting), and days to maturity (first flowers or fruits form).

You don’t want to sow seeds too early in spring and end up with spindly plants on your windowsills because it’s too cold to put them outside. Start by determining the last frost-free date in spring for your region. In the Chicago area, the date is usually about May 15, though it can arrive later. For example, if you want to get a head start growing ‘Little Firebirds’ nasturtiums, the Renee’s Garden seed packet states that the seeds should be sown indoors three weeks before the last average frost date. For the Chicago area, I count backwards from May 15, and will plant seeds indoors around April 23.

If you’re eager for spring and start the seeds too early, you can end up with leggy or diseased plants that won’t be as successful. Use the U.S. Departmen tof Agriculture’s map to find your region’s frost-free dates.

Supplies

Seedlings need light. Once the seeds germinate, you need the right amount of light, but not too much. A bright sunny window will often suffice, but placing the pots under grow lights (available at garden centers, home improvement stores and online) provides more consistent, even light. Winter sunlight is not as strong as in the summer and there’s always the chance of dull, cloudy days so supplemental light is helpful.

Some seeds, such as sweet peas, morning glories and nasturtiums have hard seed coats that slow germination. To speed things up, I scratch the seed’s hard surface with a nail file or sandpaper or I soak the seeds for an hour before sowing them.

By early May when the air temperature has warmed, I move the potted seedlings outdoors for a few hours each day until it’s time to transplant them in the garden. This is called “hardening off” and acclimates the still-tender seedlings to cooler temperatures and stronger sunlight. I put the pots in a spot that’s protected from wind and direct sunlight. I try to gradually increase the amount of time they are outdoors each day. Before long, my windowsill seedlings will fill my borders with colorful drifts. And that’s a pleasant thought on a winter day.