For the past few of years, we've used a couple of cold frames for some of our veggies - mostly leafy greens (e.g. Swiss chard, leaf lettuce, arugula, escarole, etc.) They work really great as they let us sow seeds directly outside much sooner in the spring, and the small, confined areas are easy to keep weed- and herbivore-free and well-watered. This year, I added two more frames to the backyard to increase our yield by staggering our plantings across a couple of months - this way, hopefully, we'll have a continuous supply of lettuce, chard, and carrots throughout the summer and into the fall (I plan on resowing at the end of the summer for fall, and perhaps even winter harvesting). The first cold frames I made out of plywood, some poplar 1x2s, and sheets of thin plexiglass cut to size - all bought from Home Depot. This year, I asked my grandfather, who owns a millworking business if he could cut me some plywood to size since I really don't have the right tools. Well, as I should have expected, given the way my grandfather operates, instead of plywood, I got a top-of-the-line exterior-grade composite, called Extira. It was completely unnecessary and definitely overkill, but I happily used the pieces and put the new cold frames to work this afternoon.
Into the new frames went another sowing of spring leaf lettuce mix and Swiss chard, some purple dragon carrots, and some beets. If the beet seeds look remarkably like Swiss chard seeds, it's because they're just different cultivars of the the same species - Beta vulgaris.