Curbs and mowing strips

A curbing-mowing strip combination-separating a flower bed from a lawn area can cut down on the time needed for the trimming and edging necessary to keep a garden neat. Even a mowing strip alone has advantages. It contains the lawn in a fixed area, and it helps prevent excessive water run-off because it forms a low dam around the lawn. If the strip is a foot or more wide, you can use it as a path so you don’t have to walk on wet grass or push a heavy wheelbarrow over the lawn.

Here is one way to install a curbing-mowing strip combina-tion using such materials as marble, concrete blocks, or brick for the curb, and concrete for the strip.

Soak the ground the night before you begin work. Drive 3 by 72-inch lengths of 18-gauge galvanized metal or redwood into the ground following the curvature desired. The tops of these forms should be level with the soil. Dig a trench 2% inches deep and 4!/2 inches wide, plus the thickness of the curbing material selected, behind the forms.

For the mowing strip, use a mix containing 2 parts rock and 3 parts sand to 1 part cement. Pour 1 inch of this mix in the bottom of the trench. When the concrete is firm, but not hard, set the curb in place. A little soil piled behind will help support cracks in the concrete, lay a ¼-inch reinforcing rod (two if you have adobe soil) along the mowing strip on top of this first concrete layer; or use short pieces of wood at intervals along the strip for expansion joints. Extend the rods out from the ends in case you wish to add to the strip at a later date.

Then fill the trench to the top of the metal or wood form with more concrete. Tamp with a block to bring the cement to the surface. Trowel lightly and clean the curb with a wet rag. When the concrete begins to set, trowel it smooth. After three days, remove the metal or wood form.

Use reinforcing rods in the second layer of concrete to help prevent cracking; trowel the surface smooth with a wood float.

Planting by a retaining wall

The L-shaped footing at the base of most masonry retaining walls will limit what you can plant there. You may not have the 6 to 12-inch-deep soil needed for lawn or annuals; and you’re quite unlikely to have the 24 inches or more needed for most shrubs. Nevertheless, there are several choices of plant material that will thrive in shallow soil. Also, there are several ways of building up a limited planting area at the base of a retaining wall.

If the soil is too shallow for the kind of planting you want, here are ways to solve the problem.

Shallow footing next to wall limits depth of soil for planting.

Build wood wall of 2-inch lumber to height of at least 2 feet.

Add concrete wall at lower height to hold soil for raised bed.

Set planter boxes or individual pots on 4-inch layer of gravel.

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