It’s time to start seeds for early spring annuals

It’s the new year, and it’s already time to think about spring. One of your first tasks is starting seeds for cold-tolerant, early spring annuals that require a long lead time before being planted.

When you’re getting started, follow directions on individual packets about which seeds require bottom heat, light, or darkness to germinate; you’ll need to do some research to find the specific germination requirements and determine when to start each type of seed. Some might require a short period of chilling, soaking in water, or being nicked before they’re sown. Cool-season annuals (like larkspur, snapdragon, English daisy, ranunculus, pansy, annual poppy, forget-me-not, or edging lobelia) can usually be planted outside in the garden by the second week in April, after the young plants are hardened off. This might mean you have to start seeds as much as 14 weeks ahead of time to have blooming plants ready for outside planting.

Sow your seeds in fiber pots or trays, using a premoistened, soilless or seed-starting mix. You’ll want to sow large seeds in slightly indented rows and cover them lightly with a thin layer of the mix; you can broadcast finer seeds directly on top of soil. Some seeds will need a glass or plastic cover to provide extra humidity. Water seeds from the bottom, or use a fine mister to keep the soil moist. Most seeds require a warm, bright location out of direct sun to germinate. For covered seeds, ventilate them every day, especially in bright conditions. You’ll need very good light to successfully grow these early spring annuals big enough to make a good display in the garden, since the spring season is short and there isn’t much time for plants to develop and flower outside. Many of them will start to decline as soon as the weather gets hot in summer.

When you see germination, gradually increase light levels. Most seedlings need 14 to 16 hours of direct light to manufacture enough food for healthy stems and leaves. The legginess you might see when seedlings are grown on a windowsill means the plants aren’t receiving enough light intensity, or enough hours of light. Use a full spectrum fluorescent bulb instead, and place it no more than three inches away from the foliage. When two sets of true leaves develop, transplant small seedlings to a bigger fiber pot with a slightly coarser, “growing-on” mix, and start fertilizing with quarter-strength 10-10-10 solution. As the plants get bigger, you can switch to a half-strength solution once a week.

For more information on starting seeds, come to the Garden’s Super Seed Saturday event on Jan. 24. Gardeners are invited to bring saved or leftover vegetable, flower, and herb seed packets to share and swap with other gardeners, and beginners are welcome to participate even without seeds. Talk to experts about starting seeds indoors, seed saving, and recommended varieties for Chicago gardens. For information, visit chicagobotanic.org/seedswap

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.