If you want to grow tomatoes, peppers, or other heat-loving vegetables and flowers from seed, late winter to early spring is the time to get started. You will need a sunny window or supplemental lights, pots or trays, potting mix, seeds of your choice and a little patience. While starting plants from seed is a little more work than starting with seedlings, the method greatly increases the selection of varieties and is even more satisfying when you see the first flower bloom or pick the first ripe tomato.
Start by deciding what to grow. Perhaps there is an heirloom variety of tomatoes you want to try, an unusual squash or a special flower. Peruse seed and plant catalogs, the display racks at your favorite garden center, make a trip to a seed fair or seed library, and visit with your gardening friends for ideas. Share and collaborate, since many seed packets contain more than enough seeds for an individual gardener.
Figuring out the timing is where things get tricky. You want to start seeds indoors six to eight weeks prior to the time when you want to plant them outdoors. If you are starting cool-season crops like broccoli and cabbage, they can be started anytime now to be transplanted into the garden in mid-March or later.
Warm-season crops such as tomatoes should be planted outdoors only after the chance of frost has passed. Personal preference of gardeners for planting tomatoes outdoors in the Lawrence area seems to range anywhere from early April to late May. So, if you want to transplant in early April, start the seeds in early February. But, if you want to transplant later, delay starting the seeds accordingly.
If you choose to plant warm-season crops outside in the early range, be prepared to cover or otherwise protect plants from cool or frosty temperatures. The average date of last frost in the Lawrence area is April 15.
A greenhouse, sun room or window with a full day of direct sunlight might provide enough light to get seedlings off to a good start, but most home gardeners will benefit from using supplemental lights. Purchase lighting units made specifically for plants, or use shop lights and a timer.
The amount of light produced and the proximity of the light to the seeds/plants is more important than the spectrum or bulb type. Suspend lights or set them up so that they are only a few inches above the planting trays and can be raised as plants grow. Use a timer to keep the lights on for 12 to 15 hours a day.
Select pots or trays on personal preference. For very tiny seeds, the easiest way to plant is probably to sow them broadly across a pot or tray and thin the seedlings when they grow. Larger seeds are easier to plant individually in plugs or small pots.
Use high-quality potting mix. Potting mixes labeled for seed starting generally provide better drainage than standard mix so may be the best option for gardeners who tend to overwater.
Check the seed packet or search resources for advice on planting depth. Seeds that are planted too deep or too shallow may have reduced germination rates and difficulty rooting.
After planting, keep potting mix moist but not saturated. Think of the potting mix like a sponge. The best conditions for plant growth are if the sponge has some moisture but also maintains air space within it. Too much water fills those air spaces and will drown the seedlings. But, if the sponge completely dries out, so do plant roots, and seedlings will likely perish.
Once seedlings are large enough and outdoor temperatures are appropriate for transplanting, put plants through a hardening-off period. Set plants outside (still in pots or trays) in the shade for a few hours. Do this for about a week, increasing the amount of time outdoors each day and moving to brighter shade as plants adjust. Potting mix will dry out more quickly with brighter light and spring breezes, so take care to keep plants watered appropriately during the hardening-off period.
Transplant when the plants are ready, and enjoy the rewards throughout the season.
— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.