Potatoes by St. Patrick's Day? In zone 6, the soil decides

St. Patrick’s Day is the old rule for planting potatoes, and in zone 6 it’s not a bad one. The window runs from mid-March to late April. What matters more than the date is the soil: plant once it’s dry enough to crumble in your hand rather than smear.

Potatoes go in before the average last frost, around April 21, because the shoots take two to four weeks to come up. By the time they break through, the worst frosts are usually over.

Picking your planting day

Squeeze a handful of soil. If it holds a sticky ball, wait. If it breaks apart, it’s ready. A soil thermometer reading of about 45 °F at planting depth is the other sign.

Zones are set by winter lows, not frost dates, so a frost pocket or high garden may be a week or two behind. Raised beds warm and drain sooner, and are often ready first.

Early, mid or late varieties

Type	Ready in	Examples	Plant
Early	About 70 to 90 days	Red Norland, Irish Cobbler	Mid to late March
Mid-season	About 90 to 110 days	Yukon Gold	Late March to mid-April
Late	About 110 to 140 days	Kennebec, Russet Burbank	April

Earlies give new potatoes in June and finish before the summer heat. Lates make the storage crop for fall and winter.

Preparing the seed

Use certified seed potatoes from a garden center or catalog. A couple of weeks before planting, spread them out somewhere light and cool so they grow short, green sprouts.

Cut large ones into egg-sized pieces, each with two or three eyes, and leave the cut faces to dry for a day or two. Small seed potatoes go in whole.

Planting and hilling

1. Choose a sunny spot with loose soil and compost dug in. Skip the lime, which encourages scab.
2. Plant the seed potatoes about 5 inches deep and 12 inches apart, in rows 2 feet apart.
3. When the shoots reach 6 to 8 inches, draw soil up around them, leaving the top few leaves showing.
4. Repeat every couple of weeks until the hills are about a foot high.

Hilling keeps the tubers in the dark and gives them more stem to form along. Early on, it’s also the easiest frost protection: if frost is forecast in late April, hill soil right over the young shoots or cover them with row cover.

Bush beans, fava beans and marigolds grow well alongside. Keep potatoes away from tomatoes, squash, cucumbers and zucchini.

Watering and harvest

Water deeply in dry spells, especially once the plants flower, which is when the tubers swell.

New potatoes are ready from early June, around flowering time. Feel into the side of the hill and take what you need. For storage, wait until the vines die back, leave the potatoes in the ground for two more weeks to toughen the skins, then dig on a dry day before mid-October.

Common problems

Colorado potato beetle. Yellow and black striped beetles and orange larvae on the leaves from late spring. Hand-pick them every few days.

Scab. Corky patches on the skin. Keep the soil evenly moist while tubers form.

Late blight. Brown, spreading patches on leaves in warm, wet weather. Remove affected plants and dig the crop two weeks later.

For a colder garden see potatoes in zone 5, or try potatoes in bags on a patio. Pick zone 6 on the potato page for the full window.