Starting seeds indoors can be frustrating, exhilarating, or sometimes a little of both. You can improve your success rate dramatically if you focus on what seeds need to germinate and what seedlings need to grow strong. It's not as easy as setting a pot in a window and keeping it wet, but you don't need to buy a fancy greenhouse to make them grow either. Some lights, some shelves, some sterile pots and mix, a little diluted fertilizer, and a fan are the core of the indoor garden, and following the directions on the seed packet will help too.
Let There Be Light
For seedlings to grow properly, they need light. Lots of it. Even if you have a south-facing window, chances are that you don't have enough natural light to grow healthy, robust seedlings. If seedlings don't get enough light, they will be spindly and won't make it to adulthood. Setting up an artificial light system isn't tough and doesn't have to be expensive.
You want full-spectrum bulbs in lights that you can attach to shelving above your seed flats or trays of pots. Cooler lights, such as fluorescents, can be closer to your seedlings (2 to 6 inches) than incandescents, which will dry them out. A power strip with a timer can keep the lights on your plants for 12 to 16 hours per day, error-free.
Use Self-Watering Seed Starting Systems
Never start a seed in a small peat pot. They just dry out too fast. Self-watering seed-starting systems are increasingly available on the market, but you also can make a self-watering seed starter from a plastic supermarket pie plate (one with a clear top), a container to serve as a reservoir, and some string. Poke a few holes through the pie plate and attach the strings. The strings wick water up from the reservoir to keep the planting medium moist but not wet enough to rot the seeds. While you're waiting for germination, the clear cover will keep the environment humid.
Use a Sterile Seed-Starting Medium
Just because seeds grow fine in the ground outdoors doesn't mean that you can grow indoor seeds in garden soil. Bad idea. Young seedlings are susceptible to a dreaded fungus that causes what's called “damping off.” You know you have it when all your seedlings are fine one minute and the next they have all keeled over. With all the time starting seeds requires, it makes sense to give them the best chance for survival by using a sterile planting mix, which doesn't have soil in it but is mostly sphagnum peat moss.
Sterilize Your Pots
It makes no sense to put sterile mix into dirty pots—especially if any of your seedlings have succumed to damping off in the past. Scrub off any old dirt or debris in warm water, then submerge the pots in a mild bleach solution (1 part bleach: 9 parts water) for at least 10 minutes to kill any fungus, bacteria, or parasites. After rinsing, you can air-dry them or keep them soaking in clean water until you're ready to use them.
Feed Your Seedlings
Most sterile planting mixes don't have any built-in nutrients. During germination, seedlings get all the nutrition they need from the seed itself, but after you start seeing true leaves (which come after the ground-breaking variety), you’ll want to feed your seedlings with a diluted solution of liquid fertilizer.
Ventilation and Wind
Seeds are really meant to be planted outside in the sun, rain, and wind. By planting indoors you are attempting to fool Mother Nature. Many of us even plant our seeds in our basements, the part of the house that is probably least like the natural world, with air that doesn’t move at all.
Moving air, though, is an important factor in helping seedlings to develop a robust root system and strong stems. To approximate wind, set a fan on low near your seedlings. You don't have to subject them to the equivalent of a 24-hour tornado for their size, but having them move around as they grow creates sturdier plants. If you have the fan on the same timer as your lights, you won't even have to think about it.
Read the Seed Packet
Most seed packets have a wealth of information, including whether you should even start those particular plants indoors—some plants just flat out don't like to be transplanted and are better off started in the garden in which they will live. The packet will also tell you how deep to plant your seeds—a critical piece of information. It will list how long it should take for the seed to germinate and whether you need to scarify them (nick or rub with sandpaper) to increase their chances of germination. The packet will say how many weeks before your last frost date you should start the seeds and when to transplant.
Keep the seed packet for the life of the plants. Chances are there will be information that you will need at some point (particularly if you've thrown the packet away), and you can always use it as a row marker in the garden for your seedlings until they graduate to become thriving flowers, herbs, or vegetables.
Track your successes and issues in a journal, and next winter, look at those seed packets and get the calendar ready all over again.