“I am a new member of a garden club, and I learned about other members starting plants from seeds for their gardens. I am interested in trying to do this myself. They provided some basic information, but I would like additional tips for starting seeds at home.”
— Riley Webber, Skokie
Growing plants from seed is a great way to find plant varieties that aren’t available at a garden center.
It is best to start just a few varieties of seeds, as many plants have different requirements for successful germination. You may also need to do some research to find the specific germination requirements in addition to any directions on the seed packet.
Some seeds require a short period of chilling, soaking in water or being nicked before being sown.
More Top Picks Best Sunglasses For After Cataract Surgery
Many seeds germinate more readily if you provide bottom heat. Heating mats may be purchased through plant supply companies. Different types of seeds also require different periods of time to germinate.
Use the germination and development time to decide when to start the seeds so they are ready to plant outside at the correct time.
Some seeds that are easy to start indoors include tomatoes, marigolds, basil, zinnia, coleus, nasturtium and cosmos.
Tomatoes suffer in cold weather, so time your tomatoes so they are ready to plant in the garden around Memorial Day. There are some types of vegetables, such as beans and squash, that are best suited to direct sow outdoors since they quickly germinate and grow. These types of seeds are usually marked “direct sow” on the packet.
It is too late to start seeds of cool-season annuals (larkspur, snapdragon, English daisy, ranunculus, pansy, Iceland poppy, forget-me-not), which can be planted outside in the garden by the second week in April. Iceland poppies are more sensitive to cold temperatures, so it is better to plant them outside in the third week of April most years. This may require starting seeds up to 14 weeks ahead to have blooming plants ready for outdoor planting. This group of plants is more difficult for home success, but give it a try next year.
Sow seeds in trays or fiber pots, using a fresh, premoistened, soilless or seed-starting mix. Most any kind of container (such as a small paper cup or yogurt cup) works, as long as it is 2 to 3 inches deep with a hole in the bottom for drainage. You can also start the seeds in a tray designed for seed starting and transplant the seedlings to a larger container later.
Sow large seeds in slightly indented rows or in the center of an individual pot and cover lightly with a thin layer of the mix. Finer seeds may be broadcast directly on top of soil. If you decide to sow multiple seeds into a pot, simply snip off the excess seedlings once they have germinated. Some seeds 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 produce healthy stems and leaves. The characteristic legginess that can occur when seedlings are grown on a windowsill indicates that the plants are not receiving enough light.
Use a full-spectrum fluorescent bulb that is placed about 3 inches away from the seedlings’ foliage and adjust up as the plants grow for supplemental lighting. Rotate the pots regularly to keep the plants from leaning into the light if you are growing them in a window. You may need to rotate trays growing under a light fixture too. Providing proper light levels is more important for plants that need to grow inside for six weeks and more.
When two sets of true leaves develop, transplant the small seedlings to a larger pot that contains a slightly coarser, “growing-on” mix. A plastic knife works well to lift the seedlings. Begin fertilizing with quarter-strength 10-10-10 solution about once a week. As the plant grows larger, switch to a half-strength solution once a week and reduce the fertilizer if you start to see excessive growth.
Your homegrown plants will need gradual acclimation to outdoor growing conditions — called hardening off — before planting in a bed or container.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.