Raised Planter Bed Drainage System Ideas

Aerate the Ground Below

• Normally, raised beds sit on top of the ground and the soil mix goes inside the bed frame. Water trickles down through the bed and into the ground below. But if your raised bed sits on hard, compacted soil, water won't drain properly from the bed. Before you fill the raised bed, thoroughly aerate the ground below to break up the soil and provide better drainage. For small bed areas, a hand-held aerator can work well. For large areas or for ground that is extremely hard, use a rototiller to make the job easier. Aerate down at least 6 inches, then proceed with filling your raised bed with soil and plants.

Stones or Gravel

• Other areas may have the opposite problem of hard soil -- waterlogged ground. A raised bed directly over swampy areas will hold the moisture in the bed, possibly damaging root systems of plants. These areas need an extra layer of drainage under the bed. Dig up about 6 inches of soil under the bed area and lay down a mix of gravel and small rocks, available as a soil amendment at garden centers. The rock layer will help water trickle from the bed rather than holding the moisture in the top layer of soil.

Plastic Piping Drainage

• A system of pipes hidden within the raised beds' soil can vastly improve drainage in particularly difficult growing areas. This system also is ideal for beds built over a solid structure, like a concrete slab or patio. At a garden center, buy plastic pipes at least several inches in circumference with pre-drilled holes. Alternatively, purchase solid plastic pipes and drill pea-sized holes every 3 inches. The drill holes should be on three sides of the pipes, but not the bottom. Select the least visible wall of your raised bed and drill holes large enough to fit the tubes or pipes. Create the wall holes near the bottom of the bed and spaced out about every 1 to 2 feet, depending on your drainage needs. Lay the piping in the bed and through the holes, with about 2 inches of the pipes sticking out of the back of the garden bed. Make sure the holes in the pipes face upward to catch the water trickling down, and the solid side faces down to avoid the water seeping back into the raised bed. Fill the bed as planned. As the water trickles down from the surface, some will enter the drilled holes in the piping and will be directed out of the bed.

Trenches

• A simple pebble-filled trench also can improve your raised garden bed's drainage. This method works best if the raised bed sits at a slightly higher elevation than the ground around it, as the draining water will make use of gravity. Build your bed, then pick a direction where you'd like the excess water to drain. Dig a trench several feet long and at least 3 inches wide. Make sure the trench starts at least a few inches inside the raised bed. Clear the trench of dirt, grass and debris and fill it with pebbles. This prevents the trench from refiling with dirt. Water from the bed will seek the lowest point and will trickle down the trench away from the garden.