Fans of the Matt Damon movie “The Martian” know that potatoes (Solanum tuberosum) thrive in even the most inhospitable conditions. Indeed, potatoes were first cultivated in the Andes, at elevations where maize can’t grow.
Potatoes are tubers, modified underground stems (not roots) that store energy as starch. They’re also full of protein, fiber, and vitamin C. Moreover, potatoes are virtually fat-free, so add a little butter to mashed potatoes without guilt.
This article will discuss how to grow potatoes on terra firma, from planting to harvest. It will also cover pests and diseases, and offer ideas on how to store and cook your potatoes.
Potato varieties
Potatoes are usually categorized as starchy or waxy. Starchy potatoes have thick, edible skins and are best for baking, mashing, and frying. The flesh of starchy potatoes contains little water and doesn’t stick together when cooked, yielding the dry, fluffy interior of the perfect baked potato or French fry. Waxy potatoes are low-starch and are usually boiled or roasted. Their flesh holds its shape upon cooking, making them ideal for salads and gratins. Some varieties, like Yukon Gold, have moderate starch levels and are sometimes called “all-purpose potatoes”.
Varieties also differ in size, shape, and color. Fingerling potatoes, even at maturity, are small and elongated. In other words, they’re different from new potatoes, which are harvested before maturity. New potatoes have thin skins and little starch, and can be of any variety. Both skin and flesh may be white, red, yellow, or blue/purple. The color of the skin doesn’t necessarily match the color of the flesh: some varieties have blue, red, or yellow skin and white flesh.
Seed potatoes
Virtually all potato plants are grown from cut-up potatoes, called “seed potatoes.” New plants emerge from the “eyes” (embryonic stems; see picture) in the seed potatoes. Garden stores and catalog or online sellers stock seed potatoes in early spring. It’s essential that the seed potatoes are certified free of fungal and viral diseases.
Making seed potatoes from uncertified tubers is risky because it can spread disease. Moreover, most store-bought potatoes are treated with a chemical that inhibits sprouting. Nevertheless, this document describes the process for cutting, curing, and storing seed potatoes.
Soil preparation
Potatoes need loose, well-drained soil to develop properly. If planting in a bed for the first time, work four inches of compost into the top 12 inches of soil. This is a lot of compost, and a lot of work, but the improved soil texture will be worth it. In future seasons, consider the no-till methods described in this article by Piedmont Master Gardener Ralph Morini about Fern and Cleve Campbell’s home garden. At the very minimum, loosen the soil with a broadfork or pitchfork before planting.
A soil test is also a good idea, to ensure optimal nutrition and pH. Potatoes grow best at a slightly acidic pH, between 6.0 and 6.5. The soil test results will include instructions for amending the soil.
Planting potatoes
Plant once the soil has warmed to 55℉ during daytime and stays above 45℉ at night. Potato plants are cold-tolerant, so it’s okay to plant 2-4 weeks before the last hard frost is expected. This document shows last frost dates and recommended planting dates for Virginia (PDF link).
Plant seed potatoes in furrows 3-5 inches deep, cut side down (see photo). Space the seeds according to the type of potato. For fingerlings or new potatoes, plant 10 inches apart; for really small new potatoes, as close as 8 inches. For larger (but fewer) potatoes, plant 12 inches apart. Spacing greater than 12 inches will make the tubers grow too fast, resulting in a “hollow heart,” an open space at the center of the potato.
Finish by filling the furrows with loose soil. Rake to break apart clumps, if needed, and water well to ensure contact between seed and soil.
Cultivating potato plants
Potatoes need one inch of water (2.5 quarts per square foot) per week. If irrigation is needed, water deeply once or twice per week. Mulch, such as grass clippings, will preserve soil moisture and keep weeds at bay.
As the potato plants grow, pile soil around their bases, up to an inch from the lowest leaves. Start when the plants are six inches high and repeat every 2-3 weeks. This process, termed “hilling,” will keep developing potatoes in the dark and prevent them from turning green, which causes toxic alkaloid compounds to form under their skin (PDF link).
Weed with a hoe just under the surface of the soil, to minimize damage to the tubers. As mentioned above, mulch can reduce the need for weeding.
Alternate planting methods: straw and containers
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Growing potatoes in Virginia clay is difficult, even with well-tended soil. One workaround is to grow them in straw on top of the soil. (Here’s another description of the method.) First, loosen the soil to allow good root penetration. Next, put seed potatoes on top of the soil, cut side down and spaced as discussed above (see picture). Finally, pile straw six inches deep on top of the seeds and water thoroughly (see picture). As the plants grow, add more straw to keep the developing tubers covered. By fall, the straw could be two feet high.
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Potatoes also grow well in containers, like a 15-gallon bucket with drain holes in the bottom. Start with four inches of potting soil in the bottom of the container. Put 3 or 4 seed potatoes – or fewer, for large baking potatoes – on top of the soil, then cover with four inches of soil. As the plants grow, add soil as described above. Depending on the soil mix, it might help to scatter a tablespoon or two of 10-10-10 fertilizer on top of the soil each time you add more.
Diseases and insect pests
Preventing diseases is essential: once diseases set in, they’re virtually impossible to cure. Certified disease-free seed potatoes are the best way to prevent potato diseases. Another useful method is crop rotation. Potatoes are in the Solanaceae (nightshade) family, along with tomatoes, peppers, tomatillos, and eggplant. All of these crops are susceptible to similar diseases and insects. To block transmission, plant potatoes where no Solanaceae have grown for two years. Also, planting into loose, well-drained soil will prevent root rot. Finally, practice sanitation: clean up plant litter after the growing season. This will remove disease sources and deny insects a place to over-winter.[symple_column size=”one-half” position=”first” fade_in=”false”]
In a home garden, it’s best to simply remove diseased plants. Common diseases affecting potatoes are: early and late blight (black lesions on leaves and tubers), Verticillium wilt (early yellowing and drooping), and viruses (mottled and/or curled leaves).
Insects can usually be controlled if they’re detected early. Remove Colorado potato beetles and their orange eggs (see pictures) by hand. Also look for cutworms (see picture), which sever stems at soil level. If one plant is attacked by cutworms, protect the others with aluminum foil “collars” around their bases. Finally, aphids suck the sap from plants, causing leaves to curl. More seriously, aphids can spread viruses. Personally, I’ve had success using neem oil to control aphid infestations. The VCE Pest Management Guide (PDF link) lists other treatments for serious insect problems.
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Harvest
Timing of harvest depends on the variety. Harvest new potatoes 50-60 days after planting, or when they reach the desired size. Harvest mature potatoes two weeks after the plants die back in the fall (see picture). If the plants are still growing in early fall, cut them back to six inches above soil level; this promotes maturation of the tubers. Harvest after the first light frost, but before the first heavy frost.
Harvest carefully to avoid damaging the potatoes. Push a spade, pitchfork, or broadfork into the soil a foot from the stem, then gently pull back to push the root system upward and expose the tubers. Continue doing this around the plant, or down both sides of a row. Shake or brush most of the dirt off the potatoes, but don’t scrub, which can damage the skin of even mature potatoes.
Storage
New potatoes don’t store well and should be eaten within a few days of harvest. Before storing mature potatoes, cure them at 50-60℉ at high (90%) humidity for 1-2 weeks, until the skin has thickened a bit. Long-term storage should be in the dark at high humidity, ideally at 45-55℉. If a root cellar isn’t handy, keep potatoes at cool room temperature, for example in a basement. The refrigerator isn’t the best place for storing potatoes: it’s too cold. Regardless, be absolutely sure to store potatoes in the dark, to keep them from turning green and generating toxic alkaloids.
Cooking with potatoes
Probably my favorite way to prepare potatoes is to grill or boil new potatoes or fingerlings, then toss with butter and fresh rosemary or herbes de Provence. Mashed potatoes, particularly with plenty of sour cream mixed in, are nearly as tasty. Consider steaming the potatoes, rather than boiling them, before mashing. A cheesy potato gratin is a little more work, but well worth it. Bakers can use potato flour or mashed potatoes for soft, moist bread and rolls. And last but not least, French fries are messy to cook but not impossible for the motivated home cook. They’re great with ketchup, and even better with a garlicky aioli – don’t miss Cleve Campbell’s article on growing garlic.
References and further reading
On Food and Cooking (1984, Harold McGee)
The Oxford Companion to Food (1999, Alan Davidson)
Aphids in home yards and gardens University of Minnesota Extension
Colorado potato beetles in home yards and gardens University of Minnesota Extension
Cutworms in home gardens University of Minnesota Extension
Early blight in potato North Dakota State University
Foods indigenous to the Western hemisphere: Potatoes American Indian Health and Diet Project
Grow your own potatoes Oregon State University Extension
Growing potatoes in the home garden University of Minnesota Extension
Home grounds and animals pest management guide (PDF link) Virginia Cooperative Extension
How to grow potatoes in straw Missouri State University
Late blight in potato North Dakota State University
Potato facts: Selecting, cutting, and handling seed potatoes University of Maine Cooperative Extension
Potatoes Cornell University
Potatoes are easy and fun to grow in containers University of California Agriculture and Natural Resources
Seed potato handling, transplant, sanitation, and weed control Utah State University Extension
Verticillium wilt (potato early dying) Oregon State University
Virus and viroid diseases of potato Cornell University
