Time to get your seed trays ready

Start seeds for early spring annuals that require a long lead time before being planted in the garden.

Follow directions on individual packets as to which types of seeds require bottom heat, light or darkness in order to germinate. You may need to do some research to find the specific germination requirements. Some seeds might require a short period of chilling, soaking in water or being nicked before being sown.

Cool-season annuals (larkspur, snapdragon, English daisy, ranunculus, pansy, annual poppy, forget-me-not, edging lobelia) can be planted outside in the garden by the second week in April after the small plants are hardened off in most springs. Delay the planting if spring is running unusually cold - the annual poppies tend to prefer being planted later in the month of April or early May when conditions are reliably warmer.

Sow seeds in fiber pots or trays, using a premoistened, soilless or seed-starting mix. Sow large seeds in slightly indented rows and cover lightly with a thin layer of the mix.

Finer seeds may be broadcast directly on top of soil. Some types of seeds will require a glass or plastic cover to provide supplemental 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. Ventilate covered seeds daily, especially in bright conditions.

When germination occurs, gradually increase light levels. Most seedlings require 14 to 16 hours of direct light to manufacture enough food to produce healthy stems and leaves.

The characteristic legginess that often occurs when seedlings are grown on a windowsill indicates that the plants are not receiving enough light intensity, or enough hours of light. Use a full spectrum fluorescent bulb that is placed no more than 3 inches away from the foliage.

When two sets of true leaves develop, transplant small seedlings to a larger fiber pot that contains a slightly coarser, "growing-on" mix. Continue to water from the bottom to encourage strong root development and begin fertilizing with quarter-strength 10-10-10 solution.

As the plant grows larger, switch to a half-strength solution once a week.

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