Question
We are planning a limestone rock patio for a part-shade/deep shade area (Zone 6) and would like to use some grass (Irish moss?) to fill the space between the rocks. The bed has a slight gradient, sloping towards the foundation of the house. The rocks are from a nearby quarry and are about 2-3 inches deep. How should we go about preparing the bed?

Answer
Using a shovel, level the area for the patio to within 1". Then compact the area with a small vibratory plate compactor (rent from tool rental) or use a hand held tamper. (steel bar with large flat metal plate at one end.
Then apply 2-3 inches of crushed granite and level it using a 4' level attached to a 2x4 that is about 8' long. Use the 2x4 to 'screed' the granite dust. Work it across the surface back and forth in a side to side motion, removing high areas and filling low areas. Then compact the surface again. Finally, add 1" sand for a "setting bed". Screed it and set your stones. Tamp the stones in place using small rubber hammer.
Between the stones, sweep a mixture of organic soil and then plant your moss.


Sean J Murphy, LA,ISA, LEED AP
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