How to Build a Raised Garden on a Slope

Building a raised garden bed on a slope may seem challenging. However, it simply requires slightly more planning and work than building on level ground. The cost of materials will rise with the degree of slope of the hill. Estimate the steepness of the slope before proceeding. If a terraced slope has a rise of 36 inches high for 4 feet in depth, it will require 36 pieces of 8 foot, 4x4 inch timber.

Tape measure

Shovel

Tarp

Level

4X4" timbers, 8"

Rotary saw

Drill

1" bit

Rebar

Hack saw

Heavy hammer

Select the site. It should receive at least six hours a day of sunlight and ideally should have a north/south orientation lengthwise for even sun exposure.

Measure the 8 foot face of the bed on a lower section of the slope. Remove all vegetation along the 8 feet and approximately 4 feet behind it. Place the tarp nearby and shovel the soil from the slope onto the tarp. Keep the floor of the cavity as level as possible.

Check the measurements and the level of the floor. If you don't have an 8X4' excavation, adjust. Measure the height of the back wall in inches. That's the number of timbers needed. Multiply that number by one-and-a-half. You will need six pieces of re-bar each of that length.

Choose three of the timbers. Cut one in half. Drill centered holes in all four pieces, 4 inches from one end, 7 and 7/16th inches in the other end. Drill centered holes in the 8 foot lengths 3 feet, 9 and 1/2 inches from the ends with the 4 inch holes.

Place the pieces on the floor in a herringbone pattern -- an 8 foot piece at the rear flush left, a 4 foot piece on the right flush rear, an 8 foot piece at the front flush right, a 4 foot piece on the left flush front. The end-hole pattern should also alternate with the 4 inch ends always butting the side of the piece next to it.

Pound each length of re-bar through the six holes until they're all at the height of the back wall. With the level, check the vertical plumb.

Repeat step 4. Repeat step 5 in reverse order 8 foot piece at rear flush right, 4 foot piece on right flush front, 8 foot piece at front flush left,4 foot piece on left flush rear -- placing the pieces over the re-bar. Repeat until the structure reaches the height of the back.

Turn the soil of the floor over to the depth of the shovel blade. Pour in a thoroughly combined mixture of one-third soil, one-third sand or course perlite, and one third organic matter (compost and peat moss). Fill to the top.

If terracing more than one bed on a slope, leave at least 2 feet between beds.

Be sure to choose the right timber. Pine will rot quickly. Fir will last longer. Pressure treated wood may or may not leach arsenic and copper into the soil (the EPA has a warning on this, but not an order or recommendation). In wet soil conditions, the best choice may be man-made deck material.

Wear eye protection when hammering the re-bar.

Don't skimp on the rear wall. It holds the construction together. If the soil is sandy, put extra re-bar in the back.