When to harvest potatoes and how to store them

Potatoes are one of the few garden crops you can harvest twice from the same planting. Small, tender new potatoes come early in the season, when the plants are still green, and full-size potatoes meant for winter storage come after the vines have died back. The timing you choose depends on how you plan to eat the crop, and the steps you take after digging decide how long the tubers keep.

How do you know when new potatoes are ready?

New potatoes are the young tubers you dig before the plant finishes growing. Utah State University Extension says potatoes can be harvested as soon as tubers begin forming, and University of Maryland Extension puts the window for small, tender new potatoes at 6 to 8 weeks after planting, usually once the plants have flowered. Clemson Extension adds that potatoes for use in early summer may be dug before the vines die, as soon as the tubers are large enough to eat.

You can check the size of the tubers without pulling up a whole plant. Utah State suggests digging gently into the side of the hill to see how big they have grown. If you mulched your potatoes with straw, Clemson notes that you can move the straw aside to take early potatoes and then replace it so the plants keep producing until the vines die. New potatoes have thin skins and dry out quickly, so Utah State recommends eating them soon after harvest.

When are storage potatoes ready to dig?

Potatoes you want to keep for months need mature skins, and that takes time after the plant stops growing. Utah State Extension says to dig storage potatoes after the vines have died, the tubers are full sized and the skins are mature. Maryland Extension recommends leaving the tubers in the ground for 2 weeks after the plants die back so they develop a thickened skin, and Clemson gives the same interval of about two weeks after the vines die down.

Maryland lists 90 to 120 days to maturity, and Clemson says potatoes average 100 to 120 days. According to Maryland Extension, tubers keep growing through the summer until the plants are killed by frost, mowing, insects or disease. Utah State advises reducing the water you give the plants near the end of summer, when they begin to yellow and the leaves start dying.

A simple test tells you whether the skins are ready. Utah State explains that mature potato skins are difficult to remove when rubbed, so dig one plant, rub a tuber with your thumb, and give the rest of the row more time in the ground if the skin slips off easily.

Leaving the crop in the soil too long carries its own risks. The University of California Statewide IPM Program recommends harvesting and storing tubers before a severe frost is likely, since freezing can turn the flesh gray or reddish brown and leave it tough or chalky. Where potato tuberworm is present, UC IPM also advises harvesting promptly, because the adult moths crawl through cracks in the soil to lay eggs on tubers below the surface.

How do you dig potatoes without damaging them?

Maryland Extension explains that bruises and cuts made during harvest let soil-borne fungi and bacteria into the tuber, where they cause storage rots. The steps below follow that guidance.

1. Wait for dry soil. Maryland Extension advises against digging potatoes when the soil is wet.
2. Start at the edge of the hill. Push a garden fork into the soil around the plant and lift gently, which Maryland recommends to avoid bruising or spearing tubers.
3. Lift the plant and search the loosened soil by hand. Clemson asks gardeners to handle the tubers as gently as possible and to avoid skinning them as they dig.
4. Brush off the soil and leave the potatoes unwashed. Utah State recommends letting the soil dry and brushing it off, and both Utah State and Maryland say not to wash potatoes before storage.
5. Move the harvest out of the light. Maryland and Clemson both warn against long exposure to light, which causes the green color covered further down.
6. Set aside any tuber you cut or bruise. Since wounds open the way to storage rots, plan to cook those potatoes first.

How do you cure potatoes after harvest?

Curing is a short rest in mild, humid conditions that lets the tubers heal before long storage. Utah State Extension says curing helps heal any bruises or wounds that occur during harvest, and it recommends holding the tubers at 55 to 60°F with high humidity for 2 to 3 weeks. Maryland Extension gives a range of 10 to 14 days at 50 to 60°F and high humidity, which it describes as the time needed to heal over wounds and cuts. Any space you use for curing should hold that temperature range and stay dark, since Utah State notes that light turns tubers green in storage as well as in the garden.

What is the best way to store potatoes through winter?

After curing, potatoes keep best in a place that stays cool, dark, humid and ventilated. Maryland and Clemson both describe medium cool conditions of 40 to 50°F with about 90 percent relative humidity, under which potatoes can keep for six to eight months. Utah State recommends storing cured tubers in the dark at 40 to 45°F throughout the winter.

• Keep them dark. Maryland suggests a cool basement, with the potatoes in ventilated bags or boxes kept out of the light to prevent greening.
• Keep air moving. Utah State notes that good air circulation reduces rotting and sprouting.
• Keep them cool. Maryland says sprouting and tuber rots become a problem at higher temperatures, and Clemson gives the same warning about sprouting.
• Keep fruit elsewhere. Utah State advises against storing potatoes with apples or pears, because the ethylene the fruit gives off causes the tubers to sprout.

Clemson Extension notes that late potatoes are best for winter storage, so the main crop you dig after the vines die is the one to put away.

What should you do with green, frozen or damaged potatoes?

Potatoes turn green when they are exposed to light in the garden or in storage. Maryland Extension explains that the green portions are associated with solanine, a bitter, toxic glycoalkaloid, and says they should be cut out and discarded. Utah State adds that a small amount of green can be cut away and that very green tubers should be thrown out.

Frost injury shows up inside the tuber. UC IPM describes frozen flesh that turns gray or reddish brown, usually at the end or side closest to the soil surface, along with tissue that may dry out and become tough or chalky. Tunnels in the tuber and eyes stained pink with excrement and silk point to potato tuberworm, and UC IPM recommends destroying infested tubers or storing them below 52°F to stop the larvae from developing.

How much will a row of potatoes give you?

Utah State Extension estimates 75 to 100 pounds of tubers per 100 feet of row and suggests planting 50 feet of row per person for fresh eating plus another 50 feet for storage. Utah State also notes that soils above 90°F inhibit tuber set and fill.

If you want both harvests from one garden, Maryland and Clemson suggest growing an early-maturing variety along with a medium to late variety. The early variety gives you new potatoes, and the later one gives you the tubers to cure and store. Utah State recommends planting seed pieces 14 to 21 days before your last frost date, the same date that sets the calendar in our guide on when to plant tomatoes. If tuberworm has been a problem, UC IPM recommends keeping tomatoes, eggplant and peppers away from infested potato plantings. You will find more seasonal guides in our garden section.