Indoors you have more control over growing conditions and a lot of flexibility about what time of year to plant the seeds. Use specially prepared seed-starting medium, which is available from mail-order seed companies and from garden centers. Start seeds indoors under lights, rather than in a window, for even, compact growth. Seedlings must have bright light from the moment they peer up out of the soil or they will be weak and leggy. In climates with cloudy weather or homes without south-facing windows, sun may not be reliable enough. A light garden is an ideal solution.
Set seedlings in their containers a few inches below a fluorescent shop light. You can place seedlings on a table or counter and suspend the shop light from the ceiling over them, or set up three or four tiered light stands. You can adapt ordinary shelves by attaching lights to the bottoms of the shelves and setting growing trays below each light. Put the lights on a timer set to turn on 14 hours a day and then off again (one less job for you). You can't beat the results!
Make a mini-greenhouse under lights with a clear plastic garment bag. This traps humidity near seedlings, helping to protect them from wilting. To cover nursery flats full of seedlings, bend two wire coat hangers into arches and prop them in the corners of the flat, one at each end. Work the plastic over the top of the hangers, and tuck the loose ends in below the flat. It's even easier to make a greenhouse cover for individual pots. Slide two sticks into opposite sides of the pot. Then top with the plastic and fold it under the pot.
If starting seeds in a window, take extra care to maximize light. Use a south-facing window that will receive sun all day. It should not be blocked by a protruding roof overhang or an evergreen tree or shrub. (If you don't have a south-facing window, you should consider using plant lights.) Hang foil reflectors behind the flat to keep seedlings from leaning toward the sun. If the seedlings are sitting on a windowsill, make a tent of foil behind them, with the shiny side facing the seedlings. This will reflect sunlight and illuminate the dark side of the seedlings. They will grow much sturdier and straighter as a result.
Don't transplant seedlings into a larger pot until they have one or two sets of true leaves. This allows seedlings to develop enough roots to be self-supporting, even if a few roots are lost in the process. It's also a time when seedling roots are fairly straight and compact, making them easy to separate from nearby plants. This is not as simple as counting the number of leaves on the stem, however, because the seedling usually has an extra set of leaves called cotyledons. They emerge first and store food that nourishes the sprouting seedlings. Looking closely, you can see that cotyledons are shaped differently from true leaves. Squash seedlings, for instance, have oval cotyledons, but the true leaves are broad and lobed. When transplanting, handle the seedlings by the cotyledons to prevent squashing the delicate stem.
Start seeds or cuttings in an aquarium or clear sweater box to keep humidity high. These are more permanent alternatives to makeshift options with plastic and are good for cuttings that need more overhead and rooting room than seedlings. To reuse these containers, wash them with soapy water, rinse, and sterilize with a solution of 1 part bleach to 10 parts water.
Keep reading to learn about plants from seeds outdoors.