Barb Sahl made raised beds from concrete pavers and two by fours that are sturdy enough to sit on, saving her knees. Photo taken May 7 by Barb Gorges.
Published in the Wyoming Tribune Eagle May 29, 2016, “Got rabbits? Try raised bed gardening.”
By Barb Gorges
Rabbits made her do it.
Barb Sahl, a Laramie County Master Gardener, told me she was a ground-level vegetable gardener for the first nine years at her place on Cheyenne’s south side, but she switched to raised beds to keep the rabbits out of her garden.
There were other considerations too. Raised beds would help keep her dogs from running through the radishes and it was a way to deal with a persistent weed problem.
Sahl was also thinking about her aging knees, knowing her days of kneeling would end in the future.
With that in mind, she installed eight beds using a system of landscape pavers, then added five stock tanks.
Below you will find information about the history, types and benefits of raised beds in our area.
Genesis of the raised bed
The stereotypical vegetable garden has rows of vegetables. The bare ground between must be kept weeded.
An alternative is to grow vegetables like flowers, using wide beds, 2 to 4 feet wide (depending on how far you want to reach) and grow your plants more closely. This shades out the weeds and you never step into the wide beds, keeping the soil from getting compacted. The paths between beds can be mulched.
A wide bed can be planted at ground level, or with a bit of soil excavated from what will be the paths, made into a flat-topped mound. The soil in the mound will warm up earlier in spring, allowing earlier planting, though the plants themselves may still need protection from frost at night.
If the bed is amended with compost or with soil brought in, fertility and drainage can be improved.
In 2012, I tried the mound method. I had few weeds and great results. The path around the bed was deep in tree leaves collected the previous fall. However, the edges of the mound had a tendency to erode after heavy rains.
Last summer my husband and I converted to what gardeners normally envision a raised bed to be, a contained mound.
Types of raised beds
Gardeners have been inventive at using whatever is at hand to make the walls of a raised bed: bales of straw (hay has too many seeds that will sprout), wood, rock, brick, concrete block, old stock tanks. Raised beds work for flowers as well as vegetables. Sahl even has her raspberries in one to keep them from spreading.
Wood: Raised beds can be built to workbench-level (“elevated” beds) or the sides can be as low as a single 6-inch wooden board—though that won’t keep the rabbits out. However, Sahl soon realized plain wooden boards would decompose and she would have to replace them sooner than she’d like.
Thirty years ago, raised beds using old railroad ties were fashionable, but it was found that wood preservative chemicals from that era are toxic and can migrate into vegetable plants.
Currently, “ground contact pressure treated” wood has an environmentally friendlier preservative but there is still controversy.
If in doubt, use cedar or redwood. Either, though more expensive, should last a lifetime.
Raised bed kits often contain posts with brackets that hold wooden boards. Another version I’m trying this year, available locally, is steel plates 18 inches tall and bent 90 degrees which fit around the outside corners of the bed and screw into place.
In another bed we built 15 years ago, using plastic dimensional lumber, the corners are held together by brackets on the inside. Surprisingly, the galvanized steel has not rusted out.
This detail of Sahl’s raised bed system shows the brackets used to hold the concrete pavers upright, connecting them to the 2 x 4s along the bottom and the top. She will put drip irrigation (the black plastic hoses) back in when planting the beds. Photo by Barb Gorges.
Pavers: Sahl used a system she found from Lee Valley Tools that starts with a frame of pressure treated two by fours outlining the shape of the bed. She made hers 2.5 feet wide by 8 feet long. Steel brackets attach to the frame and are designed to hold pre-cast concrete pavers upright. Sahl’s pavers are 16 inches square. More brackets along the top edge of the pavers attach to another frame of two by fours, making the structure strong enough to sit on. The brackets are ordered as a kit and the gardener buys the wood and pavers locally.
Concrete block: Mark and I tried a concrete block raised bed for our vegetables last year, but we didn’t stack the blocks on boards like Sahl did her pavers. After this past winter’s freezing and thawing, the walls undulate. Also, for the nine months of the year nothing is growing in it, the bed looks just like a pile of ugly gray concrete—right in the middle of the view from our favorite window.
Sahl’s recycled stock tank helps contain the spread of her raspberry patch. Large holes in the bottom of the tank are necessary for good drainage. Photo by Barb Gorges.
Stock tanks: This style is simpler, but perhaps harder to find, prep and install.
Sahl uses this method and got the idea from a relative who uses rusted-out tanks in her garden.
Sahl found her own stock tanks on Craig’s list. We’re talking about the long, narrow ones made of galvanized steel. Sahl’s are 2 to 2.5 feet across by 6 or 8 feet long by about 2 feet deep. Since they weren’t rusted out on the bottom, she drilled lots of holes for drainage. If she were to do it again, she suggests just cutting out portions of the bottoms.
How to install a raised bed
Find a flat, sunny location within range of your hose or drip irrigation system.
Plan the bed’s width so you can reach the middle comfortably, and maximize the dimension of materials to be used. The shape can be square, rectangular or even L or U-shaped. Sahl left enough room between beds for her wheelbarrow.
Because Sahl has a weedy infestation of skeleton-leaf bursage, she chose to cover her site with weed barrier cloth and then covered that with bark mulch between the beds.
Under normal conditions, you would remove pre-existing vegetation as you would for any other garden, especially if you aren’t building your raised bed very high—you need to allow for root growth.
Unless your building materials are ephemeral, temporary like straw bales, be sure to use a level to keep everything square and neat looking. Get corner posts set straight and boards horizontal.
How to fill a raised bed
Sahl wanted completely different soil for her beds than what was in her yard so she ordered a load that was a little sandier, with less clay. It’s important that it is good quality, she said, and not full of weed seeds. She has grown a wide variety of vegetables in the eight years since and is very happy with the results.
If you are growing vegetables, you may want to mix in a lot of compost like that available through Cheyenne’s compost facility. In future seasons you won’t have to till, just add a couple more inches of compost, perhaps in the form of the organic mulch you use on the surface—leaves and grass clippings, etc.
For flowers, be aware that hardy native perennials do best with less fertile soil.
Sahl has made tomato cages from concrete mesh that fit her raised beds perfectly. She can wrap them in plastic to protect the plants from frost early in the season.
Raised beds also lend themselves to the addition of trellises, cold frame covers, mini-hoop houses, hail guards and drip irrigation systems. See previous columns on those subjects at www.CheyenneGardenGossip.wordpress.com.
Details of Sahl’s raised beds, late August 2016: (clockwise from top left) onions, cabbage, raspberries, tomato, carrots.
Gorges raised bed, July 2016.