Three weeks ago, I started my first batch of seeds for 2012 using an ultra-basic seed-starting system: lengths of PVC pipe lined up in empty juice cartons, combined with a bag of potting mix from Home Despot, a funnel for feeding it into the pipes, and a "pusher" for extricating the seedlings when it's time to transplant them. Today, the first tiny sprout of cilantro has just poked its head above the soil, and so we're just in time to deploy the second half of the system: a new lighted tray in which to store the seedlings so that they can get additional light. Basically, it's a shallow wooden box (painted on the inside with white exterior paint to protect it from drips) with a trellis attached over the top from which the light fixture is suspended by chains. The light is hooked up to a timer (which we already had on hand) that will turn it on around 5pm, just as the daylight is fading, extending the seeds' light exposure by an extra six hours or so. As the seedlings grow, we can adjust the height of the light by shortening the chain, thus keeping the light at the appropriate distance from the tops of the seedlings. (Of course, it isn't perfect, since we'll be starting different types of seeds at different times, and it can't stay the same distance from all of them if they're all of different heights themselves. But close enough.)
The best part is that the whole contraption didn't cost that much to build. The only two components we actually bought were the light fixture itself and one two-by-four, which cost us about $29 put together. All the other components were either scavenged or left over from other projects. The plywood used for the base was left over from the new vanity that Brian built for the downstairs bath; the side pieces were left over from the new bookcase he built in October. The power cord (which wasn't included with the light fixture) was scavenged from a discarded computer peripheral, and the cup hooks holding up the chains are left over from a package of four that we bought last year to hang a curtain over our linen cupboard in the upstairs bath. As for the chains themselves, we have no idea where they came from—they were among the miscellaneous junk we found in the workshop when we bought our house, and they've been sitting their ever since, just waiting for the right project. And all the stain and paint were leftovers as well. So altogether, we've spent just under $40 on a seed-starting system that will, we hope, save us $6 to $10 each year on nursery plants, as well as allowing us to grow all kinds of interesting varieties that are only available in seed form.
We've also made an additional modification to the system: our 1.5-inch lengths of PVC pipe have been joined by some .75-inch-diameter pieces, which we're using to start leeks. Last year we tried direct-seeding them and got bupkes, so this year we're taking the advice of the gardening column in the Washington Post and starting some indoors. However, since these will be skinny little seedlings that get planted fairly tightly in the garden (12 per square foot), we knew we'd need quite a lot of them, so we decided to put them in their own tiny little starter pots that will take up less room on the tray. We can fit nineteen of these little pipettes into a single juice carton, as opposed to just eight of the full-size pipes, so we can start enough seeds for two squares' worth of leeks and still have enough room for all our tomato, pepper, and eggplant seedlings later on. And the narrower pipe didn't cost us any extra, since we had it left over from our original attempt at building garden trellises (later superseded by sturdier wooden trellises made from two-by-fours).
One final refinement was the decision to cover the individual cartons with clear plastic covers to help them retain moisture. An article that I read on seed starting in Mother Earth News noted that "Some [seed-starting trays] come with a plastic dome that will help preserve moisture...but covering trays with a sheet of plastic wrap will also work." Not having any plastic wrap to hand, I had a quick dig through the recycling bin and pulled out a plastic egg carton composed of three sections: top and bottom pieces with 12 individual cups to hold the eggs, and a flat piece that fits over the top of the whole thing. It seemed a bit like overpackaging when I first saw it, but I became reconciled to it as soon as I realized that the top piece would do just fine for a greenhouse cover. It's a bit longer than the juice cartons, but just wide enough to fit over the top, and it does in fact keep moisture in just fine (you can even watch the condensation forming on the inside of the lid, like a miniature cloud chamber). So now my little seedlings only need watering every day or two instead of twice a day, and once again, it didn't cost a penny extra.