How to Start a Raised-Bed Garden Over Gravel
Roger Cook answers 3 pertinent raised garden bed questions
I want to plant a raised-bed garden in an area now covered with 4 inches of gravel. Do I have to dig it out? How deep should the soil be? Can I use pressure-treated lumber?
—Ken Branch, Akron, OH
The depth of the raised bed depends on what you want to grow in it. Shallow-rooted herbs and radishes need only 5 or 6 inches of soil. Given the chance, peas, peppers, and beans will send roots down 36 inches or more. But most everything else should be grown in soil at least a foot deep. So dig you must.
Once the gravel is out of the way—save it to make an easy-to-weed walkway around your new bed—turn over the soil underneath because it’s probably very compacted. Go as deep as you can and lighten it with a mix of compost and sand.
I like to make the sides of these beds out of 2x lumber; it lasts longer and doesn’t bend as much as 1x material. Cedar, either western red or eastern white, is good because it’s so rot resistant, but I’ve also used spruce to save money. This is not the place for pressure-treated wood because it leaches metals into the soil.
The best soil mix for a raised bed consists of one part garden soil, one part sand, and two parts compost. It will allow water to drain and keep your raised bed from becoming a pond after a heavy rain. Leave the soil a couple of inches below the bed’s edge to keep it contained.
Shown: Roger Cook built this raised-bed vegetable garden using 2x12 spruce boards held in place with 1x cedar stakes. He set the sides four feet apart so the center of the bed would be easy to reach.