Starting seeds indoors is easier than it sounds. When I start seeds, I keep it simple, using a minimum amount of cheap equipment.
1. Plastic flats -- I prefer the black plastic ones with separate cells. Novosel Enterprises has a good selection and reasonable prices.
2. Sterilized seed starting mix -- I use Black Gold Seedling Mix, which I buy at a local nursery. Don't use regular potting soil, which is too coarse. Never use garden soil or previously-used potting soil. Avoid peat pellets because they tend to stay soggy, which causes damping-off disease.
3. Spray bottle (mister) -- To remoisten the soil while the seeds are germinating.
4. Liquid fertilizer -- Schultz brand or similar.
5. Rack to put the flats on -- Rubbermaid makes a 4-tier storage rack with enough space between the shelves to let in the sunlight. You can attach grow lights, if necessary.
6. Bright window, south or east-facing -- If you don't have adequate sunlight, hang grow lights, or cheap flourescent lights, from chains 4" above the tops of the seedlings. Leave them on for no more than 12-16 hours a day. Plants need to rest at night.
7. Fan -- Good air circulation helps prevent damping-off disease. There's a forced-air heat vent in the floor near my racks, which also helps. The goal is to keep the roots of the seedlings moist while letting the top of the soil dry out between waterings.
Now, it's time to start those seeds. Don't be scared off by all of the instructions -- it's really easier than it sounds.
Seed Starting Tips
1. Fill a flat with seed starting mix, pressing it firmly into each cell. The mix will shrink when water is added.
2. Moisten the mix with warm water. Peat moss (the main ingredient) repels cold water. My flats require about 1 quart of water. I pour it slowly over the flat, trying to put the same amount into each cell without washing out the soil. Don't waterlog the soil. When the mix is moistened, lightly press it down to remove air pockets. But don't compact it too much.
3. Wait for about half an hour for the mix to become evenly moist before you plant the seeds. If there's excess water in the bottom of the tray, pour it off.
4. Most seeds are planted 2 times as deep as they are wide. Tiny seeds like campanula are sown on the surface. Sow 5-8 seeds per cell, then lightly press them onto the surface to ensure good soil contact. Misting with water will help them settle in. To sow larger seeds, poke a shallow hole in the center. Sow about 3 seeds per cell, then cover them with soil. Don't expect 100% germination. The rate for most seeds is over 70%, but some seeds normally have a lower germination rate. That's why you should sow multiple seeds per cell. Avoid the temptation to sow dozens of tiny seeds into one cell. The seedlings won't thrive, and it'll be a thinning nightmare. Save extra seeds for possible disasters or to oversow cells with poor germination.
5. Record what you planted and the number of pony packs of each item. It helps to mark the side of the flat where you started with masking tape.
6. Place the clear plastic lid over the flat to retain humidity. Place the flat on top of the fridge or in another warm spot out of direct sunlight. As soon as the seedlings appear, remove the lid, and move the flat into the sunshine. Don't put the lid back on, or you risk getting damping-off disease (a fungus that kills young seedlings if they are too wet or don't get good air circulation). Set up a fan near the seedlings to circulate the air. This may be the single most important step for preventing damping-off disease (besides avoiding peat pellets). The fan will dry out the soil surface quickly, so you'll have to check the moisture level at least twice a day.
7. If you start seeds that require pre-chilling, such as columbine or penstemon, then place the flat in your fridge for the amount of time recommended on the packet. When the time is up, place the flat in a sunny window, and the seedlings should appear in 3-6 weeks. Remember that the plastic lid retains heat, as well as humidity. So remove the lid when the sun is shining directly on the flat. The lid can be used when the sun isn't shining, then permanently removed after the seeds sprout. See the following page for more tips on pre-chilling seeds.
8. If you have extra seeds, sow some outdoors after the last frost date, either in pots or in a prepared seed bed. Sometimes, the ones sown outdoors grow better than the ones indoors. But they're slower to germinate because of temperature variations.
9. When about half the cells in the flat are dry on top, and the flat feels light, it's time to water. Pour 1 quart of water into the bottom of the tray. Watering from the bottom up reduces the risk of damping-off disease. After a few minutes, drain off any excess water. Some cells dry out faster (like the ones in the corners), so they should be watered more often. Avoid damaging tiny seedlings. I use a mister to water until the seedlings are sturdy enough not to get knocked over. The mister is also used to keep the soil moist during germination. The most common cause of seedling death is overwatering. I give my seedlings enough water to keep them alive and growing, while allowing the soil to dry out on the surface between waterings. Seedlings can handle more water once they start spending time outside in the sunlight and fresh air.
10. After seedlings have developed their second set of leaves (the "true" leaves), start using liquid fertilizer. Use according to directions on the bottle.
11. When seedlings are sturdy enough, use a pair of manicure scissors to thin out the smallest or most gangly ones. Don't pull up the seedlings, which could damage the roots of the others. Avoid thinning fragile seedlings like snapdragons until they are well established. Thin to 2-3 plants per cell at first. When they are larger, they can be thinned to 1-2 per cell.
12. About 3-4 weeks before the last frost date, or as soon as the weather is warm, start hardening off the seedlings. Set the rack outside on the east side of your house or in the dappled shade of a tree. Only do this for half an hour the first day. Watch the seedlings closely for signs of wilting, and don't put them out on cold or windy days. Slowly increase the time, until they are staying outside all day and coming in at night. During the hardening-off phase, you may need to water more frequently to keep them from drying out.
13. It would be wise to transplant the seedlings on different days, just in case of disaster. Water them daily until they are established. Add seaweed to the first one or two waterings to encourage strong root development. Don't give in to the temptation to transplant seedlings before the last frost date, no matter how nice the weather is. One year, I transplanted 100 seedlings a few days before my last frost date (May 15), and two days later the temperature dropped to freezing. I placed pots over as many seedlings as I could, but I still lost half of them.
14. Don't be shocked and dismayed if up to 10% of your seedlings die or get eaten by bugs before they grow up. This can happen to anyone. If bugs are a serious problem, consider potting up the seedlings into 3" pots and growing them outside for a few more weeks before transplanting them into the garden. I've been known to dig up recently planted seedlings and repot them when I find them partially defoliated by insects.
15. Have fun!