Raised bed gardens: Keyhole type

Posted November 14, 2013 at 10:03 am


by Marilyn Odneal, Horticulture Adviser

A relatively new type of raised bed garden is the keyhole. A keyhole garden is 3-foot high round structure with a pie wedge cut out to access a center mesh cylinder for compost to feed the plants. The garden looks like a keyhole from above. I constructed this type of garden last winter and grew several different vegetables and herbs in it this year. Although keyhole gardens were developed in Africa to withstand hot weather and drought, I found that they worked great in our very wet summer of 2013.

It took a long time to fill up my keyhole garden and I finished shortly before planting in spring. During the summer, my mounded media sunk down about a foot under the rim of the bed, so I will need to add more soil and organic matter this dormant season. Once it settles well, I expect that I will need to add less organic matter and soil in subsequent years to sustain the level of the media.

To construct my keyhole garden, I followed the guidelines from the Texas Co-Op Power website (http://www.texascooppower.com/texas-stories/nature-outdoors/keyhole-gardening) based on the work of landscape architect Dr. Deb Tolman. Tolman promotes these gardens in her area as drought resistant and bountiful. The guidelines are as follows:

1. Measure a 6-foot diameter circle to define the inside wall of your garden.

2. Notch the circle (like cutting a wedge of pie) so you can access the basket at the center.

3. Construct the exterior wall about 3 feet high using rocks, metal, timbers or any material that can support the weight of wet soil.

4. Use wire mesh to create a tube about 1 foot in diameter and about 4 feet high. Stand the tube in the center of the circle.

5. Line the outer walls with cardboard and fill the garden area (but not the wire mesh tube in the center), with layers of compostable materials, wetting it down as you go. Fill the last few inches with compost or potting soil. The soil should slope from a high point at the top of the center basket downward to the edges of the garden.

6. Fill the center basket with alternating layers of compostable material, along with layers of kitchen scraps and herbaceous weeds that provide the plants with moisture and nutrients.

7. Water the center basket and the garden only when the plants will not survive without it. This forces the plants’ roots down toward the center basket.

8. Feed the garden by adding more kitchen scraps, lawn clippings, etc., to the center basket.

9. Consider arching a framework of thin wires over the garden. During the hottest months, the wires can support a shade cloth, and in winter, plastic sheeting creates an instant greenhouse.

10. Enjoy.

Just a note – there is a company that manufactures keyhole garden kits. If you have a gardener on your holiday gift giving list that would just love to unlock the fruits and fun of a raised bed keyhole garden, go to http://keyholefarm.com/ to have a look.

Direct comments or questions concerning this column to Marilyn Odneal via email at MarilynOdneal@missouristate.edu; write to Missouri State Fruit Experiment Station, 9740 Red Spring Road, Mountain Grove, Mo. 65711; or call (417) 547-7500. Visit our website at http://mtngrv.missouristate.edu.

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KEYHOLE GARDEN – A keyhole garden is a 3-foot-high round structure with a wedge cut out to access a center compost basket that feeds the plants. The garden looks like a keyhole from above. Vines can spill down over the edge of this raised bed instead of having to be trellised upward.