Last month I offered up some ideas for getting seed started indoors. It's not too late; summer vegetables like tomatoes and squash really shouldn't go in the ground until mid-May at the earliest. If you live near the coast like I do, it is entirely likely that temperatures won't reach tomato-friendly levels until June. So you've got some time.
But let's assume that you already have some seeds going indoors like I do, and the plants are getting larger, and your little indoor nursery is starting to get a little jungle-like. Here's what's next:
Pot it up. All those little seedlings nestled in their seed trays need to move up to larger pots. If you're like me, you probably have an embarrassingly large collection of plastic pots in the garage, so clean those with a mixture of hot water and white vinegar to kill diseases or insects and reuse them for your seedlings. I prefer 4-inch pots at this stage. If you have to buy them, most garden centers sell them for 10 or 20 cents a pot.
Get great dirt. This is really the time to splurge on high-quality potting soil. Get good, rich, organic soil so that your seedlings will stay healthy and grow quickly. This is not a good time to reuse old potting soil, which might harbor disease or being depleted of nutrients. You probably don't need to add any fertilizer right away; a good potting soil will have all the nutrients your plants need to get going. So move everything up to a larger pot, making sure to keep them labeled so you'll know what you're planting when the time comes.
Raise your lights. Now that your seedlings are taller, they're going to need a little more room under those grow lights. Some plants naturally have a more compact, low-growing habit, while others are going to shoot up and get pretty tall over the next few weeks. So you'll probably want to organize your plants according to type, keeping some underneath a low-hanging set of lights, and putting the rest under a second set of lights that will have to be adjusted constantly as the plants get taller.
Pinch back blossoms. This is not the time for a plant to bloom. If your flowers are getting ready to burst into bud, explain politely that they're getting ahead of themselves and pinch those buds off. You want your plants putting their energy into developing healthy root systems and the kind of branching structure that will allow them to bloom on multiple stems later in the season.
Feed -- a little. It's easy to burn tender seedlings by overfeeding them when they're young. Get a liquid organic fertilizer and use it at about half strength when you water. Alternate that with plain water. You want your plants to be healthy, but not stressed. Once they're in the ground, the roots will have the freedom to travel to get the soil they like best, but while they're in pots, take it easy on them.
Keep the heat going. The weather is getting warmer outside, and maybe it's getting warmer indoors where your seedlings are growing. But if you started them on heating mats, keep those mats going. The extra warmth makes them dry out quicker, which means you're going to have to water more often, but that supplemental heat source will do more to get your plants ready for the summer garden than anything else you can do.
Watch for bugs. If you started from seeds, and cleaned your pots, and used fresh potting soil, you might not have any problems with pests like aphids or whitefly. But keep an eye out for them anyway. Turn leaves over, and dig around at the base of the plant where leaves branch off from the stem. If you see any tiny little creatures sucking the life out of your seedlings, crush them under your thumb and laugh ruthlessly while you do it. Really, killing the bugs by hand is the quickest and most effective (and most satisfying) way to get rid of a small infestation on a few plants. You can also clip off infested leaves and seal them in a plastic bag, then put them in the trash outside.
For a more serious infestation, try washing the plant gently with water and dish soap, which kills soft-bodied pests. If you do feel the need to use a bug spray, be sure and buy an organic spray and use it according to directions. (Even organic sprays require some common-sense protection, so take safety precautions seriously.) Test the bug spray on one or two plants, then wait a few days to see how they handle it before you use them on the rest of your plants.
Harden them off. This is the fun part. Take your seedlings outside on warm, sunny days and let them get acquainted with the great outdoors. I leave mine out for most of the day, but I bring them indoors if the weather turns cold and windy. They'll find out about that soon enough. The idea is to gradually expose them to real sunlight and a little breeze without freaking them out completely.
Plant them gradually. Don't go crazy and plant everything outdoors on the first warm Saturday of spring. If a few plants seem like they're going to explode if you don't put them in the ground, let them sit outside in their pots for a few days and nights. If they still seem ready to go, plant one or two of them, but keep the rest indoors as back-up.
Think ahead. As soon as you've got a little room on your seed table, start another batch of seeds. You can never have too much basil. Annual flowers and sweet peas can continue to go in the garden all summer long. The real benefit of growing from seed is that you can grow what you want when you want it, so don't think of it exclusively as an early spring endeavor. Think ahead to late summer and fall crops; consider taking cuttings and propagating some perennials this summer to plant in the fall. Seeds are the ultimate economic recovery package; now that you've got a system in place, there's no reason not to keep going all year long.