When to Plant Potatoes in Colorado

Potatoes (Solanum tuberosum) are native to the Andean mountains, and well-suited to Colorado’s rugged geography and varied climate. Colorado is the fifth to sixth largest producer of potatoes in the United States, with the San Luis Valley in southeastern Colorado producing 90 percent of Colorado’s commercial potato crop. While not all of the more than 5,000 varieties preserved in Peru are available in Colorado, hundreds of varieties, from early to mid- to late season types, grow well in Colorado.

Potatoes are tubers and herbaceous perennials, hardy in U.S. Department of Agriculture plant hardiness zones 2 to 11. Plant potatoes four to six weeks before the last frost, when the ground temperature has warmed to 40 to 50 degrees Fahrenheit. In the San Luis Valley, parts of the Western Slope and other areas of Colorado with an elevation below 7,000 feet, plant potatoes in late April to early May. In more mountainous regions, wait until mid-May. Potatoes can withstand light frost, though it will kill emerging leaves. The leaves will grow back and the plant will continue to grow, though repeated freezing depletes reserves in the seed tubers.

Choose a location where the potato plants will receive at least six hours of sunlight each day. Sandy, loamy soil with a pH of 4.8 to 5.5 is ideal, though some varieties will push through clay soils and most will tolerate a more alkaline pH level. Do not plant potatoes in the same location each year, and do not plant them where other nightshade family plants were grown the previous season. Nightshade family plants include tomatoes, eggplant and peppers.

Seed potatoes look just like the potatoes you eat, though potatoes from the grocery store may have been treated to prevent sprouting. You can replant potatoes you grew the previous year, but after one or two growing seasons, the potatoes will no longer produce well. Seed potato producers grow seed potato from the sprouts that emerge from potatoes. These sprouts are rooted and cultivated to produce the seed tuber. Any seed potato imported into Colorado must be certified as free of disease.

Seed potatoes that are 1 to 3 ounces, or about the size of an egg, can be planted whole. Cut larger seed potatoes into pieces of about the same size, as long as each piece has at least one or two "eyes" or sprouts. Handle seed potatoes carefully, taking care to not break off the emerging sprouts. Dig a trench 6 to 8 inches deep, and plant the seed potatoes or pieces 18 inches apart, in rows 2 feet apart. Cover them with 4 inches of soil. Water well and check the moisture level where the potatoes are growing to avoid overwatering. Potatoes can withstand less water, while too much may cause the tubers to rot or develop diseases.

Sprouts should emerge in about two weeks; when they are 8 inches high, hill the plants by raking up soil from the sides of the bed to add another 4 inches of soil around each sprout. Repeat this hilling process every two to three weeks as the plants grow, taking care to not disturb the soil where the tubers are growing. Be sure to cover any tubers that push to the surface with soil.