Covering raised beds is not much harder than covering regular garden plots to protect against frost. Be sure to cover them the night the first frost is predicted in your area. Keep in mind that some tender vegetables should be harvested, if needed, before covering, as they will not stand up to any frost. All your harvesting should be done before the first hard frost or snow.
Cut poles to hold up your plant covers. These can be wooden, plastic or metal, as long as you are able to cut them to the height you want. The poles should be slightly taller off the ground than the height of your tallest plant in the bed.
Poke the poles into the ground at each corner of the raised bed. If they are long beds, sink some poles into the ground along the sides as well, enough to keep a cover up in between the poles. A pole every four or five feet will work best.
Drape old bed sheets, blankets, tarps or throw cloths over the poles, so that the covers are not crushing the plants. If you need several sheets or cloths for one bed, use a heavy-duty stapler to fasten the edges of the cloths together so they don't fall and crush the plants or let frost in.
Weight down the extra material that overflows the edges of the beds. Use large rocks on the corners and along the edges to keep the covers pinned to the ground so they will not blow off on windy nights.
For plants outside the beds or covers, turn a plastic bucket or flowerpot upside down over the plants to shield them from frost. If you think they may blow off, put a large rock on top to keep them down.