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The first three raised garden beds were constructed in April 2012 and four more were constructed in April 2013. Each raised bed is essentially a box with 2-foot high walls that is recessed into the ground so that only 1-foot of the wall height appears above ground. The raised bed design provides the following benefits:

  • provides an organized appearance to the garden
  • clearly identifies the garden beds and walkways
  • resists burrowing into the garden beds by gophers and moles
  • resists penetration of the garden beds by eucalyptus roots
  • convenient height for students to sit or kneel on when reaching into a garden bed

The raised garden bed frames (or walls) were constructed of three courses of 16"x8"x8" concrete block (CMU) since that is the least expensive, permanent, construction material available in our area. Before constructing the frame for each bed,  the soil in the bed area (mostly sand) was excavated 11 inches down. Then two layers of poultry wire  (metal mesh) and a root barrier (6-mil polyethylene sheet) were placed across the bottom of the bed. Then the first course of the concrete block wall was placed on top of the plastic sheet.

[In 2013 the bottom of the each bed was constructed from 1/2" thick concrete board in lieu of poultry wire. The plastic sheet was placed in the hole below the concrete board. In addition to blocking burrowing animals, the concrete board provides a firm, level floor on which to stack the first course of block.]

A second CMU layer was stacked on the first and the polyethylene sheet was wrapped over the second course block on sides of the bed (not the ends - to allow for drainage). Then the  third course was stacked on the second course thereby holding the plastic sheet firmly in place. A cap block was placed on top of the third course.

Some of the excavated dirt was filled in around the outside of the block up to the level of the existing walkway grade. A mixture of compost (1 cubic yard per bed) and the remainder of the excavated dirt was used to fill the bed so that the soil level inside the bed is 12 inches higher than the soil surrounding the bed (at the top of the third course). The resulting soil depth in the bed will be 24 inches and it is composed of approximately 50 percent original soil and 50 percent compost. 

[In 2013, the large L-shaped beds required 2 cubic yards of compost per bed.]