Keyhole Gardening Technique

Keyhole gardening adds interest, intrigue to landscape

Bill Sevier: Ask a Master Gardener

Saturday, December 5, 2015

Q: There was a keyhole garden on display by Master Gardeners at the state fair. Can you explain this? Craig, Tulsa.

A: Unique gardening techniques, such as square-foot gardening and lasagna gardening, interest and intrigue adventuresome gardeners — and keyhole gardening is no exception.

The technique was first made popular in sub-Saharan Africa, where it was recognized to be a method of growing green vegetables with limited water supply. In the U.S., it has been popularized by environmental scientist Deb Tolman, Ph.D. A summary of her suggestions for a keyhole garden with photographs of many different variations may be found at inspirationgreen.com.

The basic idea for the structure is simple. Usually it is a circular raised-bed garden 3-4 feet tall and about 6 feet across, with a wedge removed for access. From above, it looks like a keyhole or a pie with a skinny slice removed. In the center of the bed is an upright circular tube structure 3-4 feet tall and 1 foot in diameter, usually made of wire mesh. The height of the bed, the tube and the materials used to construct it have many variations. The outer wall is usually made of stone, wood, plastic or metal.

Often, cardboard is used inside the bed on the sides to prevent leakage and as fill. The bed, all but the center wire tube, may be filled with layers of a variety of organic material such as cardboard, paper, manure, leaves, straw and old potting soil. Thin layers of garden soil are often added between these layers. All of the organics should be watered as added. The top 5-6 inches can be compost, good garden soil or potting soil. This will be used for planting. The top of the bed should slope from the center tube downward to the outside wall to promote drainage.

The center tube, which has been made accessible by the wedged slot in the bed, is used to add alternating layers of green (nitrogen) and brown (carbon) garden wastes. This also includes all kitchen scraps except dairy, fats and meats.

The central composting tube is also where water is added to the garden. With irrigation of the tube, the composting process of the organics goes fast, and water and nutrients (compost tea) leak into the surrounding bed. This conserves water and encourages the plants to put down deep roots.

The keyhole garden will allow you to grow many types of vegetables, especially the green leafy ones, using less water and fertilizer in a smaller space. It is versatile and accessible for the physically limited. With little effort, a frame may be constructed on which to place a cooling shade cloth in summer. The same frame can be covered with plastic sheeting as winter approaches, making a cold frame for extending your vegetables’ growing seasons.

Garden tips

§  Proper care will extend the life of Poinsettias through the holiday season and beyond. They need to have the brightest light possible and be kept away from cold windows and heating vents. They prefer a room temperature of 65-75 degrees. They will die or perform poorly with too much or too little water. Feel the soil, and when the top inch or so is dry, water with lukewarm water until water emerges from the bottom of the pot. Discard this water. There is no need for fertilizer.

§  If your roses have not been mulched do so now. This is a good place to use those fall leaves that have been shredded with a mulching mower. Mulch not only will prevent cold damage to those plants that are susceptible, but also will prevent warming of soil on warm winter days, which may promote premature cold-sensitive new growth.