Mr. Rawles:
The biggest drawback of raised planting beds is their greater need for water. Water leaks out and evaporates from the sides of the planting beds, as well as normal bottom drainage. If water is scarce, or you have to supply it manually, this drawback can become serious.
Simple solution: when constructing the raised planting bed, place a plastic liner along the inner walls all around, sealing it with sturdy plastic tape. Do not put the plastic on the bottom of the raised bed, or you will have a mud bathtub with no drainage at all. This will keep all the moisture inside the bed, preventing leakage and evaporation from the side walls.
If you want the plastic to last forever, you can buy polycarbonate plastic, which can take hundreds of pounds of pressure. GrowersSupply.com [1] carries it.
Also, a suggestion for an easy way to make permanent raised beds that don’t rot, and don’t suffer from frost heave problems. Make them out of those decorative concrete “rocks” that are carried by most garden supply places. These are normally used on slopes for terracing, and along patios for flower beds. They can be made to any height, and all you have to do is lay them on top of each other. The inside of the walls can then be lined with plastic.
The walls are meant to look a little rough and irregular. There is no mortar, so there is no cracking from frost or settling. They come in a variety of colors and styles, and can easily be formed into any shape you want, unlike wood, which is mostly limited to squares and rectangles. If you want to change the shape or size, just move the blocks. No carpentry, no concrete mixing.
If you want extra free water, set the blocks so that they tilt slightly inward, toward the bed. Rain falling on the top blocks will flow into the bed, adding extra moisture.
This can be important for OPSEC [2], as it is easy to arrange the beds in typical landscaping style curves, scatter in some flowers, and make you veggies disappear. Well, maybe not the tomatoes. – Mary M.