Potato (Solanum tuberosum) crop failure is often the result of heavy soil that compacts and stays wet, but potato cages, made from wire fencing bent into a cylinder, are filled with a combination of light, finished compost and straw, and the open sides help soil dry. The tall cage provides more space for potatoes to grow, which leads to a greater potato harvest. This method also works well for teaching kids how food grows.
The cage should measure two to three feet in diameter and about three feet tall, which you can achieve with 3-foot-wide wire fencing cut to 7 1/2- to 10-foot lengths. The holes in the wire grid should measure about two inches to keep soil in place while allowing it to breathe. Bend the fencing into a cylinder and secure the ends with either aluminum tie wires or plastic zip ties. Dig a hole about eight inches deep and the same diameter as the cage; set the cage inside so the lower eight inches is below grade. Stakes are not necessary with sturdy fencing, but flimsy fencing such as chicken wire can benefit from three or four evenly spaced rebar stakes set in the ground and tied to the fence.
Each cage is large enough to plant about five seed potatoes, but you should plant each cage with the same variety of potatoes, so harvest times are the same. Cut large seed potatoes into two-inch chunks, each with at least two eyes. Fill in the bottom of the cage with six inches of clean topsoil and finished compost mixed in equal parts. After spacing the seed potatoes evenly apart on top of the soil mixture, cover them with another two inches of the soil and compost mixture up to soil grade. The soil must be kept evenly moist while the potatoes sprout and the plants grow, but avoid overwatering, because the seeds can rot in wet soil.
The seed potatoes should sprout above the soil within a couple of weeks. When the stems reach about six inches tall, pull a few leaves around the perimeter of the cage out through the holes in the cage. Fill in the cage with a mixture of finished compost and straw, leaving about two inches of the leaves uncovered. It also helps to line the cage with straw to prevent the compost from falling out the sides. Repeat this process as the plants grow another six inches. Stop filling the cage when the cage is about three-fourths full or when the plants begin flowering, which indicates that potatoes are forming -- whichever comes first. Stop watering the plants when flowers develop.
Potatoes are ready to harvest when the leaves and stems die, usually 90 to 120 days after planting, depending on the variety. If you plan to store the potatoes over winter, leave them in the soil for another week or two to toughen the skins. When they're ready to harvest, simply remove the ties and pull the cage away from the mound. This is a great time to convince the kids to do the gardening labor for you. Let the kids dig through the compost and straw to find the potatoes -- tell them it's a treasure hunt and they'll have a blast. You'll find potatoes throughout the entire height of the cage, along with several potatoes at ground level where you planted the seed potatoes.