Do you long for a nice little greenhouse to start your spring vegetables and flowers, but don't have the room, ability, or money to build one? Perhaps making a cold frame might be the answer. It doesn't even have to be permanent. All you need is some heavy duty clear plastic, or some old windows, and you can grow all kinds of things in preparation for the spring, as well as save yourself a basketful of money. You will need a well drained area that gets nearly all day sunshine, and it is best if it is also sheltered from the wind just so that a strong spring storm won't destroy it before you are ready. It will be fine to put it under deciduous trees, because when they sprout leaves you will be done with your cold frame anyhow.
Next, find some plywood for the sides, and you are ready to go. Think of a cold frame as a rectangular box with a sloped top that is hinged on the tall side with the windows facing the south. Instead of lumber, which makes a more or less permanent structure, and not a very pretty one at that, you could use bales of hay for the sides and plastic for the top, and dismantle it when you are finished with it. Then use the hay for mulch, and throw away, or store the plastic sheeting. You could also put windows, or clear corrugated fiberglass sheets on top of the hay bales and store these when you are done, also. That way, at least your yard looks straightened up without a forlorn, weed infested cold frame looking at you all summer. One of the nice things about a cold frame is that you will be able to grow all sorts of perennial flowers that are difficult to start otherwise, but are expensive to buy potted.
Most perennials such as: purple coneflower, black-eyed Susan, yarrow, and agastache, just for starters, will not sprout unless the night temperatures stay around 45-50F. You can sprout them in your refrigerator, but it sure is nice to keep the dirt outside where it belongs. Another great thing about a cold frame is that you can move out the flats of frost hardy flowers and vegetables such as snapdragons, sweet peas, cabbages, and broccoli, early in the spring, and then next get a jump start on things more tender such as tomatoes and peppers. The plants will need almost all day sunshine, because for one, the sun warms the potting soil during the day, and second, the new seedlings make energy from sunlight and will not grow very well in the shade.
The main mistakes most novices make when building their first cold frame is that it is usually too small, too short, and not narrow enough to reach across without standing in it. A useful size is at least 10 feet long, and not so wide that you can't reach across to the back to tend to the plants. The back of the cold frame should at least be two feet tall and sloped to the front to shed rain and make it sturdier against a strong wind. The front should be at least one foot tall or even more, so that the sturdy seedlings will not touch the top before you are ready to set them out. I have the best results using a fine grade of potting soil in disposable aluminum roasting pans with holes punched in the bottom, and setting this in another aluminum roasting pan as the watering tray. You can also cheaply buy plastic flats and trays from a nursery site online, but you'll probably be required to buy a lot more than what you need of them, and they don't last for very many seasons.
To prevent damping off (which is a nurseryman's term for a premature death due to a fungus that rots the stems and roots) the flats will need to be perfectly drained, and never sit in a constant puddle. After the seeds sprout you will want to step them up into individual peat pots. You must keep the soil a little moist, but allow it to dry somewhat in between watering. Too wet is just as bad as too dry. To be sure that the peat pots never remain in a puddle, you might consider placing them on old pallets, gravel, or bricks to keep them up off the ground. Another thing to consider is how to water. Tiny seedlings are very susceptible to a hard rain or water spray. You will need to use a very gentle watering spray, or set the flats in trays, and then drain them when the soil has gotten soaked. Rain water is best just because most of us in this area have very hard water. All that lime in the water makes the pH of the soil go up very high with all the necessary daily watering. Another thing to consider is heat. As you know, Texas can have warm days during the winter, and underneath glass or plastic it can easily reach temperatures that will quickly cook your babies. If it gets too cold with one of our annual cold snaps, you can set a heat-lamp inside your cold frame. All you need to do is keep the temperature somewhere between freezing and 70F to have success. If you want to get fancy, you can buy thermometers that operate an automatic window adjuster to raise and lower the top. (But if you had the money to do that you would probably just build a green house, or buy your plants already potted.)
Obviously, by now you are getting the idea that you are going to be married to flats of tiny seedling for several months, and if you need to travel, or can't keep them watered, sheltered, or drained as needed, you'd best just buy your seedlings from a nursery. But then, of course, you'll not have enough to give away pots of transplants to appreciative family and friends, and you would miss out on a really fun time growing plants all winter. If you don't have a greenhouse, a cold frame really is a necessity for gardening addicts. It keeps us sane and less irascible during the winter. Then when other people are out spending lots of money on weak, root-bound potted plants, we gardening addicts can spend our extra money on more gardening stuff. All the coddling, and worry about cool nights, or hot days will be forgotten, and chortling over our wealth, we can set out all the fat healthy transplants we want, then we'll worry about what to do with the leftovers.