What to do now
Mildest step first.
- Check the soil 4 inches down in the morning; plant once it stays at 45°F or warmer and crumbles instead of sticking together.
- Cut large seed potatoes into pieces about 1½ inches across, each with at least one eye, and let the cut sides dry for a few days.
- Plant the pieces about 4 inches deep and 8 to 12 inches apart, sprouts facing up.
Not sure this is it? Check other potato problems
When to plant
Potatoes are a , and they are planted before the last frost. The University of Maryland puts them with the semi-hardy crops to plant 2 to 4 weeks before the average last frost, and Utah State suggests 2 to 3 weeks. Colorado State is more cautious and says 0 to 2 weeks before. In a cold spring, or where late frosts are common, the later end of that range is safer.
Soil temperature
Soil temperature matters more than the calendar. Penn State, UC and Colorado State all say to plant when the soil reaches 45°F, while Utah State asks for at least 50°F. The soil should also be dry enough to crumble in your hand. UC IPM notes that seed pieces in cool soil that is too wet or too dry are more likely to rot. The "Can I plant this week?" check on the potato page uses 45°F.
Preparing seed potatoes
Buy certified, disease-free seed potatoes. Penn State advises against grocery store potatoes, which may be treated to keep them from sprouting. Small seed potatoes, about 1 to 1½ inches across, can be planted whole. Cut larger ones into pieces of about 1½ inches (Utah State says at least 2 ounces), each with at least one eye. Penn State suggests spreading the cut pieces out at 60 to 70°F for a few days so the cut surfaces heal, and Clemson says to cut them 3 to 5 days before planting. UC IPM, however, suggests planting cut pieces right away, so either works if the soil is in good shape.
Depth and spacing
Penn State suggests a 4-inch-deep trench with the pieces 8 to 12 inches apart and the sprouts facing up, covered with 4 inches of soil. Clemson gives 3 to 5 inches deep and 8 to 10 inches apart, and Utah State 4 to 6 inches deep and 10 to 12 inches apart.
If frost hits the shoots
Sources differ on how much frost young potato plants can take. Clemson says they resist a light frost, while South Dakota State says the leaves have no frost tolerance. Iowa State explains that frost can blacken the leaf edges or kill all the growth above ground, but even badly damaged plants usually send up new shoots within 10 to 14 days, and there is no need to replant. If a hard frost is forecast soon after shoots appear, a overnight gives extra protection.
Growing it again? When to plant potato for your ZIP code
- How do you grow potatoes in a container or grow bag?Use an opaque 10–15 gallon container with drainage holes, filled with potting mix and compost. Plant 2–3 certified seed potato pieces and keep adding mix as the stems grow.
- My potato plants flowered — why are there no potatoes?Flowering doesn't mean potatoes are ready. At bloom, tubers are often only new-potato size, and they keep growing until the vines die. If you find few, look at soil heat near 80°F, too much nitrogen, dry spells and hilling.
- Why are my potatoes green, and are they safe to eat?Potatoes turn green when light reaches them. The green comes with natural toxins called glycoalkaloids. Peel slightly green potatoes deeply. Throw out ones that are heavily green or taste bitter.
- What soil temperature do I need to plant vegetables?It depends on the crop. Lettuce, spinach and onion seeds can sprout in soil as cold as 35°F. Peas, carrots, beets, radishes, cabbage and kale need about 40°F, potatoes 45°F, and corn and tomatoes 50°F. Beans, cucumbers, peppers, squash and melons need 60°F. Seeds come up faster and more evenly when the soil is well above these minimums.