Spring seems like a long way off, but in the gardening world, it is closer than we think. Seed catalogues are out, which gives the avid gardener an itch this time of year.
“Many gardeners like to get a head start by planting their own seedlings indoors,” says Sheldon Gerhardt, North Dakota State University Extension Service agent. “It sounds like a simple task, but it takes more effort than one thinks. Just ask anyone who has worked in a greenhouse.”
Lighting is probably the most common problem gardeners face when starting seeds. Without adequate light, seedlings will end up leggy, pale and weak. Natural light is great, but seedlings should have up to 16 hours of light a day, so supplemental light usually is necessary.
Combining warm-white and cool-white fluorescent bulbs creates a good spectrum of light. Having the light fixture on chains also is beneficial because the light should be very close to the seedlings (no more than an inch away). If the seedlings are grown on a windowsill, try to avoid drafty areas.
Soil is another important factor that may be overlooked.
“You should be able to find a high-quality planting mix locally or make your own from a mixture of equal amounts of vermiculite, milled sphagnum moss and perlite,” Gerhardt says. “Don’t use plain garden soil. It can get rock hard after a few waterings and carry insect and disease problems. The damping-off fungus is a common problem that causes young plants to suddenly keel over at the soil line and die. Using sterile soil, avoiding over-watering and having adequate ventilation can help avoid this problem.”
Fertilization is not necessary for seeds because they carry their own food and have enough food energy to germinate on their own. On the other hand, young seedlings will need a weak fertilizer to grow successfully. As the seedlings get bigger and have several sets of true leaves, the dose can be increased to full strength, but follow the directions on the label.
Seeds need to be kept constantly moist to germinate. The consistency of a just wrung-out sponge is a good standard to use. Once the seedlings are up, begin watering them slightly less often. When they are at least a few inches tall, it is OK to let the top half-inch or so of soil have a chance to dry out between waterings. Check the soil with your finger on a daily basis. Too much moisture can cause root rot and damping-off problems.
“Thinning is a critically important step,” Gerhardt says. “It usually is hard for first-time gardeners to discard seedlings that were carefully nurtured, but it is a necessary step. Overcrowded seedlings always develop into inferior plants. Their roots become intertwined, crowded, weaker, more disease prone, leggy and chlorotic. Thinning should begin as soon as the seedlings have their first set of true leaves. Small scissors should be used for thinning. Yanking them out disturbs the roots and soil of the remaining plants.”
Tender seedlings grown indoors under constant conditions need to be gradually acclimated to the harsher outdoor environment so they can withstand the exposure to direct sun, wind and changing temperatures. This process is called hardening off. When the weather is warm and settled both day and night, set seedling containers outdoors in a lightly shaded, sheltered spot. Gradually increase the time the plants spend outdoors until the seedlings spend a half-day outside and then increase the time to a full 24 hours. Next is the transition into sunlight. Begin with just a few hours of full sun. Gradually increase the time in the sun to a half-day and then several full days in the sun before transplanting the seedlings to a permanent spot in the garden when there is no more danger of frost.