Zone 5 potatoes go in from late March, ahead of the last frost

Seed potatoes go into zone 5 ground from late March to early May. That’s before the average last frost around April 30, which is fine: potatoes take two to four weeks to push shoots through the soil, and by then the worst frost is usually over.

The real signal is the soil. Plant once it’s dry enough to crumble in your hand rather than smear, and has started to warm. Cold, wet soil rots seed potatoes.

Early, mid or late varieties

Potatoes take anywhere from 70 to 140 days to crop, depending on the variety.

Type	Ready in	Examples	Use for
Early	About 70 to 90 days	Red Norland	New potatoes in early summer
Mid-season	About 90 to 110 days	Yukon Gold	Summer and fall eating
Late	About 110 to 140 days	Kennebec	Storage through winter

In zone 5 there’s time for all three. Plant earlies first in late March or early April, and lates by early May, so they finish before the first frost around mid-October.

Getting seed potatoes ready

Buy certified seed potatoes, which are free of disease. Grocery potatoes may carry disease and are often treated to stop sprouting.

Two or three weeks before planting, set them in a tray somewhere light and cool, around 60 °F, to grow short, sturdy green sprouts. This is called chitting or greensprouting, and it gives them a head start. Cut large potatoes into egg-sized pieces with two or three eyes each, and let the cut surfaces dry for a day or two.

Planting

1. Choose a sunny spot with loose soil. Dig in compost, but don’t add lime, which encourages potato scab.
2. Dig a trench or individual holes about 5 inches deep.
3. Set the seed potatoes 12 inches apart, sprouts up, in rows 2 feet apart.
4. Cover with soil and rake level.

Hilling

As the shoots reach 6 to 8 inches, draw soil up around the stems to leave just the top few leaves showing. Repeat every couple of weeks until the hills are about a foot high, or the plants meet across the rows.

Hilling does two jobs. New potatoes form along the buried stem, and the soil keeps light off them. Potatoes exposed to light turn green, and the green parts aren’t safe to eat. Early on, hilling also protects young shoots from frost.

Frost and watering

Potato leaves are damaged by frost. If frost is forecast after the shoots are up in late April or early May, hill soil right over them or cover the row with row cover overnight. Blackened shoots usually regrow, but it sets the plants back.

Water deeply in dry spells once the plants are growing well, and especially once they flower, which is when the tubers swell. Uneven watering gives knobby or hollow potatoes.

Bush beans and marigolds grow well near potatoes. Keep them away from tomatoes, squash, cucumbers and zucchini, which share diseases or compete for space.

Harvesting

New potatoes are ready from mid-June, around when the plants flower. Feel gently into the side of the hill and take a few, or dig a whole plant.

For storage, wait until the vines have yellowed and died back, then leave the potatoes in the ground for two more weeks so the skins set. Dig on a dry day, by mid-October, before the ground gets cold. Let them dry for a few hours out of the sun, then store them somewhere dark, cool and humid.

Common problems

Colorado potato beetle. Striped beetles and orange larvae stripping the leaves. Check plants every few days from June and pick them off.

Scab. Rough, corky patches on the skin, worse in dry, alkaline soil. Water steadily and skip the lime.

Late blight. Brown patches on leaves that spread fast in warm, wet weather. Remove affected foliage, and dig the crop two weeks later.

Set zone 5 on the potato page to see the full planting and harvest window, or grow a few in potato bags if space is short.