If you want to get an earlier jump on spring planting or extend your gardening later into fall, adding a cold frame or low tunnel to your raised bed could provide the magic you need. Because raised beds isolate your soil, these covers can warm the ground more quickly and maintain a higher average temperature more easily. You’ll sometimes see black plastic row covers warming the soil in commercial nurseries, but experts agree that clear plastic is more effective. They are 10 degrees warmer than black plastic and 15 to 20 degrees warmer than uncovered soil.
Agricultural supply manufacturers make a wide range of materials that can be used in row covers to protect crops from hail, cold temperatures, insects, and intense heat. These include shade cloths, greenhouse plastic, woven fabrics like Agribon, unwoven fabrics like Reemay, and others. You can also get inventive. Tulle makes an effective row cover against insects, so if you find a deal at your fabric store, why not give it a try?
Low tunnels are effectively small greenhouses that are non-permanent, inexpensive, easy to construct, and beneficial for making your growing season a bit longer. Low tunnels are 3 to 6 feet wide, and you can install them before planting, but they can make working the soil difficult, so keep an eye on the timing of your low tunnel construction.
