Visual Landscape Highlights
Grades in the landscape can create visual challenges, grades of over 5 percent are too steep for comfort or for best appearance. Where there are such differences in grade on a small lot you should put in steps and a terraced slope or retaining wall to connect the two levels.
The most comfortable steps for a garden path have a 5-inch rise and a 14-inch tread, though a 6-inch rise and a I 2-inch tread are satisfactory. Anything steeper is uncomfortable, particularly if it is made of flagstone with a rough surface.
Terraced slopes should never rise more than 1 foot in 2 feet and are much better at a rise of 1 foot in 3, particularly if a power mower is to be used. If the banks are too steep to make grass cutting easy, it is much better to plant them with ground covers than with grass.
A stone retaining wall is always an attractive way to make up the difference in grade. It gives much more character to a garden than a terraced slope does. However, a wall, shelter or outdoor fireplace made from brick or stone set in mortar will not stand up in Northern climates unless it is on solid concrete footings that go down below the frost line. This makes the wall too expensive for most properties.
Provided the drainage in the soil is good, a dry stone wall – one without mortar can be set on a footing of coarse gravel or crushed stone 8 to 12 inches deep and 15 to 18 inches wide. Dig the trench for the footing deep enough for the lowest course (layer) of stone in the wall to be buried 2 to 3 inches below the lower grade. For best appearance like building your river rock landscape, build a wall of flat-bedded lime- or sand-stone from 2 to 4 inches thick, with an occasional thicker piece to avoid monotonous horizontal lines. Always place the bed or grain of the stone horizontally and level, with the trimmed face showing. As you lay each course in place, to a tight line running the full length of the wall, use a straight-edged board and carpenter’s level to make the courses level. Fill in with earth packed firmly behind each course. Set every fifth or sixth stone with a short face to the front so that the length of the stone goes back into the bank as an anchor.
For safety’s sake, do not build a wall like this over 30 inches high, and for the coping (top layer) use broad, flat stones set in concrete mortar. This may crack if the wall heaves from frost, but it will settle back in place afterwards.
Also, for strength and river rock landscaping, it is a good idea to build the wall with a slight “batter” – lean toward the back of 1 to 2 inches for each foot of rise.
Build the steps into the wall as it is put up, rather than setting them in later. Have each tread all of one stone, if this is possible, and wide enough so that the step above can overlap the one beneath by 2 to 3 inches.
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