Potatoes are relatively inexpensive to purchase, but freshly dug potatoes from your home garden have a flavor all their own. Oval baking potatoes and red potatoes have dominated the market, but there are actually over 1,000 different varieties of potatoes available for growing, including many heirloom potatoes. The texture of potatoes, even more so than the flavor, is very different from variety to variety.
When you grow potatoes, you never really know how you're doing until you harvest—and then it's too late to change things. The starchy tubers grow hidden underground as the top half of the plant matures. The potato can be finicky to grow, because of pest and disease problems, but also very rewarding.
- Botanical name: Solanum tuberosum
- Common name: Potato
- Plant type: Annual tuber
- Mature size: 1.5 to 3 feet
- Sun exposure: Full sun
- Soil type: Loamy
- Soil pH: 5.0 to 6.0
- Bloom time: Summer
- Flower color: Violet
- Hardiness zones: Since potatoes are grown and harvested as an annual in zones 3 through 10b, USDA hardiness zones do not apply.
- Native area: Andes mountains of South America
How to Grow Potatoes
Cold climate gardeners plant potatoes in mid to late spring. In a warm climate, you would do best planting in either late summer or late winter, so the plants aren't trying to grow during the hottest months.
To extend your potato growing season, choose an early variety and a later, main season variety. You plant these at the same time, but the late season variety is harvested several weeks after you've already dug the main season potatoes.
Buy certified disease-free seed potatoes. Planting potatoes from the grocery store is a gamble. Besides the disease problem, potatoes, like many produce aisle vegetables, are often treated with a growth inhibitor to keep them from sprouting. Don't plant your potatoes where tomatoes or eggplant were grown the year before. These are in the same family as potatoes and can attract similar pests and problems.
To keep the top growth growing, plant potatoes should in full sun. They can handle partial shade, but it's the lush top growth that feeds the tubers underground. The more sun, the better—at least six hours per day. The tubers need to be protected from the sun if they grow near the surface or they will turn green. Hilling is done to prevent this, which is simply mounding soil up near the stem of the plant as it grows.
Grow your potatoes in soil with a pH between 5.0 and 6.0. Potatoes grown in soils with a higher pH seem prone to scab, which produces rough spots on the potato. Potatoes don't like particularly rich soil. If you have a good amount of organic matter in the soil and the pH is neutral to acidic, the potatoes should be happy. The soil needs to be loose and well-draining. If you have soil that is heavy in clay, you will need to prepare it down to the depth where the potato tubers will grow.
Potato plants rely on a steady water supply. Water them at least an inch a week. They are sensitive to drought conditions—especially when they flower, as that is the peak time for forming the potato tubers. Mulching around the plants can help retain moisture.
Temperature and Humidity
Potatoes should not be planted until the soil temperature reaches 40 degrees Fahrenheit. Summer crops do best in areas where the summers are cool, as the potato tubers grow best when the soil temperature is 60 to 70 degrees Fahrenheit, and stop growing when the soil hits 80 degrees Fahrenheit. Mulching around the plant, such as with a thick layer of straw, can keep the soil as much as 10 degrees Fahrenheit cooler. Areas with hot summers often plant potatoes as a winter crop. They don't require humidity.
You can fertilize your potatoes with an organic, slow-release fertilizer when you plant them. Every couple of weeks, give them a feeding with diluted liquid fertilizer or fish emulsion.
Planting and Potting
Choose a sunny spot with well-draining, loose soil, so that the roots and tubers can develop. There are three methods you can use:
- Trench method: A traditional potato planting method involves digging a shallow trench about six inches deep and placing the seed potatoes in the trench, eyes facing up. Then cover the potatoes with a couple of inches of soil. As the potato plant grows, the soil is continually hilled up along the sides of the plants. This keeps the soil around the developing tubers loose and keeps the surface tubers from being exposed to sunlight, which will turn them green and somewhat toxic. Hill the soil whenever the plants reach about four to six inches in height. You can stop hilling when the plants begin to flower.
- Scatter method: Some gardeners prefer to simply lay the seed potatoes right on the soil and then cover them with a few inches of mulch. You can continue layering mulch as the plants grow. If you have a rodent problem, this method is probably not your best choice.
- Container method: The container method makes hilling easy and takes up less space. Plant your seed potatoes in the bottom of a tall container, like a clean garbage can or whiskey barrel. Put about six inches of soil in the bottom first, then spread out your seed potatoes. Keep adding soil as the plants get taller. You could use peat instead of soil. It's lighter to work with and the lower pH prevents potato scab disease.
Seed potatoes aren't really seeds at all. They are full-size potatoes that are allowed to start producing shoots from the potato eyes. You've probably seen this happen when you've stored potatoes in the kitchen for too long.
Seed potatoes can be planted whole or cut into pieces, with each piece containing an eye or two (or three). Because potatoes can rot if the soil is too cool or wet, many gardeners prefer to allow the cut pieces to callus over, by leaving them exposed overnight. You can also purchase a powdered fungicide for dusting onto the pieces, to avoid rotting.
Varieties of Potatoes
If you want to try growing different kinds of potatoes, look for these:
- Irish Cobbler: This early season potato can be planted as soon as the ground dries.
- Kennebec & Katahdin: This variety is good for storing.
- French Fingerling: These long, slender, red-skinned potatoes don't need peeling.
- All Blue: These are fun to surprise people with and are good keepers.
Expect to wait two to four months for potatoes to reach their full size. The entire crop is ready to harvest once the tops of the plants die off. You can leave the potatoes in the ground for a few weeks longer, as long as the ground is not wet.
New potatoes are small, immature potatoes. You can harvest a few of these without harm to the plant once the plant reaches about a foot in height. Gently feel around in the soil near the plant and lift them out.
Harvest carefully, by hand or with a shovel. Turn the soil over and search through for treasure. The tubers can branch out and digging in with a fork is a sure fire way of stabbing a potato or two. They're still edible, but they won't keep for long.
Pests and Diseases
Potatoes are prone to problems, so be on the lookout for these:
- Beetles and aphids will defoliate the plants. Monitor early in the season, before they become a major problem. Check the undersides of leaves for the eggs and larvae of common beetle pests like the Colorado potato beetle. You can usually remove these by hand.
- Thin, red wireworms attack underground. Rotating where you plant your potatoes each year will help avoid wireworms.
- Scab is a common potato disease that looks like raised, corky areas on the skin or sunken holes on the surface. A low soil pH will help control scab. Add peat moss to the planting area.
- Late blight (the cause of the Irish potato famine) turns the foliage black, then moldy. Burn or dispose of the foliage. Do not compost it. The potatoes can still be harvested, but you should wait several weeks. To avoid this problem, use certified disease-resistant seed potatoes.
Toxicity of Potatoes
The poisonous compound solanine is found in any green areas or sprouts of the plant and tuber. It is toxic even in small amounts to humans, dogs, and cats. When the plant is growing, ensure you don't eat any of the leaves or greenery. For the potato tubers, throw them away when they turn green below the skin or have black spoiled areas. Cut out the eyes and remove any sprouts before eating. You can experience vomiting, stomach pain, diarrhea, fever, and delirium from this poisoning, which often appears 8 to 10 hours after ingestion. Seek immediate medical help.