Although you can grow some potato varieties from seed, it’s easier to plant certified, disease-free “seed potatoes” purchased from garden centers or Internet and catalog suppliers. (Potatoes you buy at the grocery store are often chemically treated to prevent the eyes from sprouting.) You’ll need 5 to 8 pounds of potatoes to plant a 100-foot row. Along with standards such as ‘Katahdin’, try some colored potatoes like ‘All Blue’, ‘Rose Gold’, ‘Purple Peruvian’, and ‘Cranberry Red’.
Potatoes need space, sunshine, and fertile, well-drained soil. Acid soil provides good growing conditions and reduces the chance of a common disease called scab.
Plant seed potatoes whole, or cut them into good-sized pieces, each of which should contain 2 or 3 eyes. Cure the cut pieces by spreading them out in a bright, airy place for 24 hours, or until they are slightly dry and the cut areas have hardened. In wet climates, some gardeners take the precaution of dusting seed potatoes with sulfur to help prevent rot.
Plant early cultivars 2 to 3 weeks before the last spring frost or as soon as you can work the soil. Time the planting of late cultivars so they will mature before the first fall frost.
Plant potatoes in rows spaced 3 feet apart. Place the seed pieces 6 inches apart, and cover them with 4 to 5 inches of soil. As the vines grow, hill soil, leaves, straw, or compost over them to keep the developing tubers covered. (When exposed to sunlight, tubers turn green and develop a mildly toxic substance called solanine.) Leaving only a small portion of the growing vines exposed encourages additional root development.
Most growers prefer to plant potatoes in hills or in mulch mounds. The mulch-planting method is especially good for growing potatoes in containers, such as large barrels. This “dirtless” method makes harvesting extremely clean and easy but can produce a smaller crop of small tubers.
Once the plants blossom, stop hilling up the soil, and apply a thick mulch to conserve moisture and keep down weeds. Water deeply during dry spells.
Climate and growing conditions can create a number of problems. Speckle leaf, a disorder that appears as dark splotches on leaves with sunken areas on the leaf undersides, is apparently caused by too much ozone in the atmosphere. Breeders are developing resistant cultivars. Keeping plants healthy and well cultivated is the best prevention.
Hollow areas in tuber centers are caused by rapid and uneven growth. To prevent this, plant seed potatoes closer together, cut down on watering and fertilizer, and avoid susceptible cultivars.
Other possible pests include blister beetles, leafhoppers, and wireworms. Blister beetles are ¾ inch long, slender, dark-colored insects that feed on leaves; reduce damage by hand picking (be sure to wear gloves to avoid blisters). Thin, wedge-shaped, ¼-inch-long leafhoppers cause 493leaves to curl and yellow; apply soap spray for control. Wireworms are ½- to ¾-inch-long larvae of the click beetle; these orange “worms” feed on and damage developing tubers. They are more prevalent in newly cultivated areas, so wait a few years after converting a lawn area into garden to plant potatoes there; crop rotation and frequent cultivation can also help.
An intriguing development in pest control is varieties such as ‘Prince Hairy’ and ‘King Harry.’ These varieties discourage leafhopper and Colorado potato beetles from feeding by virtue of their hairy leaves. The hairs contain sticky fluid that leaks out when hairs are touched, coating the insects with goo.
Avoid most potato diseases by rotating crops, providing good air circulation, keeping the garden clean, selecting resistant cultivars, and planting disease-free seed potatoes. If disease does strike, remove and destroy affected plants. Here are some diseases that might occur:
- Black leg, a bacterial infection, begins as yellowing of top foliage and progresses to a black, slimy rot that destroys stems and tubers.
- Early blight, also called leaf spot, is a fungus that shows up on leaves as enlarging brown spots that develop concentric rings. The blight eventually spreads to the tubers, reducing yields and creating puckered skins with discolored spots.
- Late blight hits crops after they’ve blossomed. It begins with dark, watery spots on leaves and spreads to stems and tubers.
- Ring rot is a highly infectious bacterial disease that is not generally obvious above-ground. Underground, it starts with a ⅛-inch ring of decay under a tuber’s skin; eventually the whole interior decays, leaving a shell of firm tissue.
- Scab causes rough, corky spots on tubers. It is most commonly a problem in soils that have a near-neutral or alkaline pH or in those that are on the dry side. Keep the pH low and maintain an even moisture level in the soil to avoid scab.
- Verticillium wilt turns older leaves yellow and eventually causes the whole plant to wilt and die.
Blossoming plants are a sign that the first “new” potatoes are ready to harvest. Pull aside the earth around the base of plants and gently pick off cooking-sized tubers, which are delicious boiled with the skins on.
Once the foliage starts to wither and die back, the tubers will be fully grown. If the weather is not too warm or wet, they will keep in the ground for several weeks. Dig them up with a spading fork before the first frost. Potatoes that are nicked or bruised during harvesting won’t store well, so eat them as soon as you can. Clean and dry the crop as quickly as possible, but never expose it to sunlight. Store tubers in a dark place at around 40°F.
Note that potatoes with colored flesh often lose that color when cooked in water. To keep red and purple potatoes colorful, try roasting them instead of boiling.