Potato (Solanum tuberosum) is arguably one of the world's most important food plants and commercial crops, providing an enormous volume of nutrients and digestible carbohydrates in the tuberous roots. Over centuries, these annual root vegetables have held off famine and starvation in many regions of the world, and few vegetables are more versatile.
Potatoes are a member of the nightshade (Solanum) family of plants, a group that contains a number of important food vegetables, including tomatoes, eggplant, and peppers. Like those plants, potatoes contain toxic alkaloid compounds in the leaves and other green parts. But the mature roots of potatoes are deliciously edible.
Potatoes are relatively inexpensive to purchase, but freshly dug potatoes from your own home garden seem to 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. At any given time, home gardeners have at least 100 varieties of seed potatoes that readily available. The texture of and shape of the potatoes, even more so than the flavor, is very different from variety to variety, especially with heirloom potatoes.
In northern regions, seed potatoes can be planted when the soil can be worked, after the last chance of frost. The soil temperature should ideally be at least 50 degrees Fahrenheit. In warmer southern climates, potatoes are usually planted as a winter crop; planting time can be anywhere from September to February. Time to full maturity can range anywhere from 90 to 120 days, depending on the variety. Small early potatoes are usually ready to harvest about 55 days after planting.
|Botanical Name||Solanum tuberosum|
|Common Name||Potato, Irish potato|
|Plant Type||Annual tuberous vegetable|
|Size||1 1/2 to 3 ft. tall; similar spread|
|Sun Exposure||Full sun|
|Soil pH||Acidic (5.0 to 6.0)|
|Hardiness Zones||Annual vegetable grown in zones 3-10|
|Native Area||Andes regions of South America|
|Toxicity||Green parts are toxic|
How to Plant Potatoes
Cold-climate gardeners usually plant potatoes in mid to late spring. In a warm climate, you will do best planting in either late summer or late winter, so the plants aren't trying to grow during the hottest months.
It's fairly easy to grow potatoes successfully if you follow some basic guidelines:
- To extend your potato growing season, choose an early variety as well as a late-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. Attempting to plant potatoes purchased from the grocery store is a gamble. Besides the disease problem, potatoes are often treated with a growth inhibitor to keep them from sprouting.
- Don't plant potatoes where tomatoes or eggplant were grown the year before. These are in the same nightshade family as potatoes and can attract similar pests and problems.
Planting potatoes can be done in one of two ways: a trench-and-hill method that involves adding soil around the stem as it grows upward, and a simple scatter method.
- Trench method: A traditional potato planting method involves digging a shallow trench about 6 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 it keeps the surface tubers from being exposed to sunlight, which will turn them green and somewhat toxic. Add soil to the hill whenever the plants reach about 4 to 6 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.
To bolster top growth, which will support the growth of the roots, plant potatoes in full sun. They can handle part 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 an acidic 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 1 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 at least 40 degrees Fahrenheit, and preferably 50 degrees. 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. Potatoes don't have a preference when it comes to air 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.
There are more than 100 varieties of potatoes commonly sold, generally divided into three categories:
- Russets and long white potatoes, which work well for potatoes that will be baked, boiled, or fried
- Round white potatoes, which are most commonly used if you will boil potatoes, or use them to make potato chips
- Red-skinned potatoes, which are frequently used for boiling, baking, or in potato salads
Within these categories, varieties are divided into early, mid-season, and late potatoes. Some popular cultivars include:
Popular varieties grown for early-season harvest include:
- ‘Irish Cobbler’ has a tannish skin and irregular shape. It works well for boiling and mashing.
- ‘Norland’ has red skin and is known to be resistant to potato scab.
- ‘Mountain Rose’ has red skin and pink flesh; it is known to be resistant to some viruses.
Popular varieties grown for mid-season harvest include:
- ‘Red Pontiac’ has red skin. It is considered one of the easiest red potatoes to grow.
- ‘Viking’ is a very productive red-skin potato.
- ‘Chieftan’ is a red-skin potato known to be resistant to potato scab. It stores well.
- 'Yukon Gold' is a very popular thin-skinned potato with yellow flesh. It has no eyes.
Popular varieties grown for late-season harvest include:
- ‘Katahdin’ has tan skin as is resistant to some viruses.
- ‘Kennebec’ is another tan-skinned potato. It is bred to be resistant to some viruses, as well as late blight.
- ‘Elba’ is a tan-skin potato with large round tubers; it resists blight and potato scab.
If you want to try growing some unique potatoes, look for these:
- 'Irish Cobbler' is an early-season potato that can be planted as soon as the ground dries.
- 'Kennebec & Katahdin' is a variety known to be good for storing.
- 'French Fingerling' is a long, slender, red-skinned potato that doesn't need peeling.
- 'All Blue' is an unusual blue potato that keeps well.
A member of the nightshade family of plants, potatoes contain alkaloid compounds in the leaves and other green parts, which can cause cell disruption leading to digestive symptoms including vomiting, abdominal pain, and diarrhea. Even the edible roots have very small amounts of these compounds, though cooking generally destroys most of the toxins. The potato skins have a somewhat higher concentration of the alkaloids, but unless the skin is green, there is usually not much danger to eating cooked potato skins. But potatoes with green skins or black spoiled areas should be thrown away. And the eyes, which contain larger concentrations of the toxic alkaloids, should be cut out and thrown away.
More serious is the quantity of toxin found in the green leaves and stems. Pets, people, or grazing animals that eat copious amounts of potato foliage and stems may get seriously ill, or even die. Symptoms may appear as much as 8 to 10 hours after ingestion. Seek medical help if symptoms occur.
Seed potatoes aren't really seeds at all. They are full-size potatoes bred for the purpose. They 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.
New potatoes are small, immature potatoes. You can harvest a few of these without harm to the plant once the plant reaches about 1 foot in height—about 50 days after planting. When the plant is in flower, the new potatoes are generally ready to harvest. Gently feel around in the soil near the plant and lift them out.
Expect to wait two to four months (up to 120 days) 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.
Harvest carefully, by hand or with a shovel or 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. Damaged potatoes are still edible, but they won't keep for long.
Common Pests and Diseases
Potatoes are prone to problems, so look out 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.
Growing Potatoes in Pots
The container method avoids the complications of hilling and takes up less space. It can be done in a tall container, such as a clean garbage can, whiskey barrel, or a 5-gallon pail; or in a planting bag designed for this purpose. Put about 6 inches of soil in the bottom first, then spread out your seed potatoes. Keep adding soil or peat as the plants get taller. Peat is lighter to work with and the acidic pH prevents potato scab disease.