Frustrated with having to grow tomatoes behind your garage or peppers in pots on the deck because you rocky sloping lot, though attractive, isn’t garden friendly? A raised garden bed may be just what you need. Expensive? Will you need a construction firm to build it? Nah; an 8 foot square raised bed built on even a steep 15% slope should cost well under $100 and take almost any homeowner a long Saturday afternoon to complete.
You probably have a spot in mind; a good-sun-throughout -the-day-but good-for-little-else location. The retaining walls can be built of cast stone, bricks, adobe, or timbers. Treated landscape timbers are by far the least expensive and easiest to work with and that’s what we’ll use in the building example. Like any project, first visualize the end result and placement then gather the following basic tools: spade, carpenters level, 10 foot tape measure, carpenter square, sawhorses, hammer/#16d 3 1/2 long galvanized nails, caulk gun/ 3 “liquid nails” adhesive cartridges, saw (an electric chainsaw is best, a bowsaw distant second), 40 # bag of sand, 4 stakes/twine, wheelbarrow/shovel to transport dirt/compost, leather gloves & safety glasses. We’ll determine how many timbers we’ll need a little later.
OK, lets begin laying out the plot. Since timbers come in standard 8 foot lengths, this illustration will deal in 8 foot dimensions but obviously your size of plot will determine wall dimensions. Place a stake in the uphill end of the plot, measure down 8 feet and place the downhill stake. Measure laterally 8 feet and spot the other two corners. To check for squareness, do a diagonal measurement, (from trig class, 1.414 x 96=135 3/4 in our case), make any needed adjustments and stretch the twine around the stakes to layout the plot perimeter. Using the spade, dig a 2 inch deep x 5-6 inch wide trough around the inside of the twine keeping the bottom reasonably flat.
Now to determine the number of timbers needed. Using an 8 foot straight edge, a 2×4 will do, place one end at the uphill corner, hold the straightedge level, (use the level), and measure down to the downhill corner base. On a sheet of graph paper, use a large scale, (i inch of paper = 1 foot of measurement), sketch the side wall outline. Timbers measure 3 inches thick across the flats so starting with the flat top of the triangle, draw horizontal lines every 3 inches. There you have the lengths of all the side timbers. Since full length timbers will be used only for the top layer, the sides and lower walls will be the only full walls. All the side timbers will lbe cut to an approximate slope-corresponding angle and the uphill wall will be the slope itself.
Using the graph ratio, determine how many timbers you will need and you’ll know whether to use the SUV, cadge the neighbor’s pickup, or have Home Depot deliver.
With all materials now gathered, it’s sawing time. Start with the front wall bottom timber and layout a 45 degree angle, (for a 90 deg. miter), on each end and cut. Lay in place in the trench using sand and loose soil to level. Tamp the soil well along the length to firmly set this base layer. For the side base, measure cut a mating 45 degree angle. Then, using the sketch, measure the length, mark the approximate angle, and cut. Again, use the level mating the mitered end to the front timber, and level. Do the same with the opposite wall and when satisfied, nail the mitered ends securely. Check again for level and squareness and firmly tamp soil around the base. There you have the foundation.
The rest is like stacking layers of blocks. Miter the 45 degree ends and cut each length per the sketch. It’s best to inset each row by about a1/4 for stability and appearance so cut the lengths accordingly. Liberally apply the adhesive between layers and angle nail every 18 inches to the lower rail. Continue on up to the full top layer. Don’t be too critical of your mitered joints; timbers are supposed to be rustic.
Leaving 2-4 inches of soil around the insider of the timbers, dig down the top and sidewall soil approximately 12 inches minimum, discarding the turf but using the rest as fill dirt at the low end of the bed. Phone shop and locate a landscape supplier to deliver probably a yard of dirt/compost mixture to you driveway.Wheel that around to level your bed to the top of the timbers. Plant/stake/mound/feed/ and water and you have a a raised bed that will provide a tasty array of produce all summer long or a beautiful array of flowers.
The raised bed will hold ground heat and provide a longer fall growing period and covering with a plastic sheet converts the bed to an early spring hotbox to jump-start seedling.
Happy gardening!
