The terrain of our 150 acre timberland is much like the Ozarks of south
Missouri with ridges and hollers. After a daunting climb off the lonely road,
our home is placed well back into the timber atop one of those ridges.
With the ground falling off in almost every direction the idea came to us
that terracing would be the best approach for establishing a shade garden.
The construction of terraced walls using large limestone rocks would be
the most esthetically pleasing, but without a good selection of suitable
material on the place, we opted to purchase the typical land-scaping blocks
available at our local building supply stores. These blocks do not have the
natural beauty of real stone but are utilitarian, structurally sound, and
economical. We opted to leave about 100 ft of green space between the
house and our first wall, and we wanted the wall to feel natural and free flowing. The undulating shape of our first wall twists and
rambles serendipitously along the side of the falling ridge for a length of about 120 ft. As with agricultural terraces, the idea was
to follow along the side of a ridge while staying at about the same elevation. Such a terrace below our home lifts the gardens for viewing, captures the rain runoff, prevents erosion, and aids irrigation.
While the foundation for these manufactured walls is important, we don’t go overboard with preparations. Our soils are quite compact with a generous proportion of clay beneath a relatively shallow layer of top soil. Using a flat shovel Phil scratches out a general path just deep enough to clearly see the trajectory of the finished wall. The curves should be gentle and pleasing to the eye. After establishing the path of the wall, we locate the lowest elevation point (if water were poured anywhere along this path, it would flow out at this location). This low point is the starting place for the wall construction. Depending upon the terrain, this starting point could be at the tail end of a wall or anywhere along its length. Phil prepares the foundation and constructs the wall simultaneously. With a flat shovel he digs down about 3-5 inches along the previously marked path, long enough to lay two or three blocks. On our ridge this depth has cleared away the loose surface material down to undisturbed, somewhat compacted clay soil. Sandier soils would require deeper excavations and other methods to guarantee a solid foundation. We then lay 3/8” crushed limestone to a depth of about 3” in the short, shallow trench. The landscaping blocks that we use weigh 22 lbs and are about 12” long and 4” thick (as seen in the attached photographs). While compaction of the gravel with a tamper is a good thing, we do not do so. Using a torpedo level, a heavy ball peen hammer, and a 2x4 wooden block, Phil strikes the concrete block repeatedly to settle it in place. The leveling process requires frequent strokes at pertinent strike points on the block to achieve level in both the X and Y planes. These various strokes also compress the gravel which is necessary for a stable wall.
The process continues by laying adjacent blocks while achieving good compaction and level. As the torpedo level is moved across the surface of the laid blocks, a smooth transition assures that the blocks are level with each other. Since this process began at the lowest elevation point, the added blocks are working their way deeper into the ground. When a block has become buried to its full depth, that block marks the end of the first layer and it’s time to add the second. The second layer is stacked alternately on top of the first, meaning new blocks are centered
upon two blocks in the row below. At the end points, the final block
has only one lower block to rest upon. In order to stabilize these
row ending blocks, remove some dirt and add gravel underneath.
This method continues until the desired wall height is reached.
For this size landscaping blocks, six courses high is the maximum.
Now, we're ready to begin the backfill. If the wall is more than
3 or 4 rows high, we add approximately 5-6 inches of 1” gravel
to the inside base of the wall for drainage. If the low elevation
point is somewhere in the middle of the wall, we also install a
2” pvc drain pipe under the starting block (we're building a
well-drained raised bed, not a pond). We are fortunate enough
to have accessible bottom ground which has good, rich alluvial soil.
Now the seemingly endless trips begin with Phil's faithful tractor
of hauling up bucket after bucket of dirt until the final grade blends
in aesthetically with the top of the finished wall. Because of the
shallow wall foundation, the first layer of blocks is completely backfilled on the outside of the wall for added stability. The terraced garden is now complete. As the ridge falls down the hill, a second wall begs to be constructed, then a third, and a fourth, etc..
Standing at the bottom of the ridge looking back up at the multiple terraces covered in hostas is a beauty to behold.