How to Grow Potatoes: A Complete Guide for Cold Climates

Potato quick facts

On this page

• Potato quick facts
• Seed potatoes or supermarket potatoes — does it matter?
• First early, second early or maincrop: which should you grow?
• Do you need to chit potatoes?
• When should you plant potatoes?
• Zone chart: planting, hilling and harvest for USDA zones 3–6
• How to plant potatoes step by step
• Hilling: why, when and how much
• Watering, feeding and weeds
• Potatoes in raised beds, grow bags and under straw
• Late blight and tuber rot — spotting it and stopping it in time
• Scab, green tubers and other problems
• When and how do you harvest potatoes?
• Storing potatoes: temperature, darkness and shelf life
• How many potatoes do you get per square metre?
• Crop rotation: how often can potatoes go in the same bed?
• Common mistakes
• Frequently asked questions

Seed potatoes or supermarket potatoes — does it matter?

It matters more than anything else on this page. Certified seed potatoes are grown under an official inspection scheme: the crop is checked in the field and the lot tested for virus and disease before it can be sold.

A potato from the produce aisle has been tested for nothing. It may carry leafroll virus, potato virus Y or blackleg with no visible sign, and it may have come from a field with potato cyst nematode — cysts that survive in soil for decades. Many are also sprout-inhibited, so they sulk or never emerge.

For a home garden, ordinary certified seed is plenty. Buy early while the variety choice is good, and pick tubers of 35–55 g (1.5–2 oz), roughly hen's-egg size. Very large tubers throw many weak shoots, very small ones make a weak plant.

Potato cyst nematode

Potato cyst nematodes are microscopic roundworms that feed on the roots and leave cysts in the soil. They spread mainly on seed tubers and on soil carried by tools, boots and potting mix. The symptoms mimic poor feeding: small plants that yellow early and set few small tubers, with pinhead-sized pale brown beads on the roots at harvest. Some varieties carry partial resistance, but the effective protection is certified seed plus a long rotation. In several countries these nematodes are regulated pests worth reporting.

Saving your own seed is possible, but virus accumulates year on year and quietly erodes the yield. Replace your stock every third year, and never save from a season when blight ran through the patch.

First early, second early or maincrop: which should you grow?

Potatoes are grouped by how long they need to finish. That choice decides when you start digging, how much you get, and whether anything is still edible at Christmas.

Count backwards from your first autumn frost. In USDA zone 3, with roughly 90 frost-free days, a 130-day maincrop will not finish, so the plot goes to earlies. In zone 6 you can run all four groups and stagger the digging from midsummer to October.

Waxy or floury — what is the difference?

Waxy potatoes hold their shape when boiled and suit salads, gratins and new potatoes with butter — 'Charlotte', 'Nicola', 'Anya'. Floury potatoes break down and go fluffy: 'King Edward', 'Maris Piper', 'Russet Burbank'. Texture comes from dry matter content, and conditions shift it: dry soil and modest nitrogen give a flourier tuber, heavy watering and feeding a waxier one.

Varieties that stand up to blight

If blight has wrecked your crop several years running, variety choice does more than anything else. 'Sarpo Mira' and 'Sarpo Axona' are the best-known resistant maincrops; 'Cara', 'Setanta' and 'Valor' also hold up. The alternative is to grow only earlies and lift them before blight arrives.

Do you need to chit potatoes?

No. Potatoes grow perfectly well from an unsprouted tuber. But chitting — letting them push short shoots before planting — brings the harvest forward two to three weeks, and in a 90 to 120-day season that is a large slice of the year.

The gain is biggest with earlies, where a fortnight decides whether you eat new potatoes in July or August. For maincrops it is smaller but real: the plant establishes faster and sets more tubers before blight arrives.

Start four to six weeks before planting. Stand the tubers in a single layer in egg boxes or trays, rose end — the end carrying most eyes — upwards, somewhere bright, cool and frost-free at 10–15 °C (50–60 °F). Aim for short, stubby, dark green or purple shoots no longer than 2 cm (3/4 in). Long white thread-like shoots mean too warm and too dark, and they snap off as you plant.

The full routine, including what to do with tubers that have chitted too far, is in the guide to chitting potatoes. Cutting large seed tubers works if each piece keeps two eyes and weighs about 40 g (1.5 oz); let the cut faces cork over at room temperature for two or three days first, since a fresh cut face in cold wet soil rots easily.

When should you plant potatoes?

Soil temperature decides, not the calendar. Potatoes start growing at about 7 °C (45 °F) at planting depth and grow away properly at 10 °C (50 °F). In colder ground the tuber just sits, and the longer it sits the greater the risk it rots.

In practice that means two to three weeks before your average last frost: mid to late April in USDA zone 6, early May in zone 5, mid to late May in zone 4, and the first days of June in zone 3. A soil thermometer removes the guesswork — take a reading at 10 cm (4 in) in the morning, three days running.

Frost after emergence

The tuber underground copes with cold. The foliage does not: it is killed at around −2 °C (28 °F). When frost is forecast and the shoots are just up, pull soil over them in the evening or lay row cover over the bed. Frosted foliage usually regrows, but the crop is delayed a fortnight.

Dates by zone and what to do if you are planting late are covered in the guide to when to plant potatoes.

Zone chart: planting, hilling and harvest for USDA zones 3–6

Zone ratings describe winter cold, and potatoes are annual here, so the numbers are shorthand for how long your season is. The chart assumes chitted seed. A south-facing sandy bed can run ten days ahead of a north-facing clay bed in the same zone.

Planting dates differ by about six weeks between zone 6 and zone 3, but the window for lifting a storage crop shrinks from six weeks to almost nothing. That is why variety choice matters more the colder your zone — a 130-day maincrop in zone 3 rarely sets a storable skin — and why chitting stops being optional in zones 3 and 4.

How to plant potatoes step by step

For a household plot this is about half an hour of work.

1. Pick the site. Full sun, open to air movement, and ground that has not carried potatoes or tomatoes for three to four years. Leaves dry faster on an open site, which lowers blight pressure.
2. Prepare the soil. Loosen to 25–30 cm (10–12 in) and work in well-rotted compost, about 5 litres per m². Never fresh manure — it drives leafy growth, soft tubers and scab. Do not lime the same year.
3. Draw the furrows 10–12 cm (4–5 in) deep, 60 cm (24 in) apart for earlies and 75 cm (30 in) for maincrops — those wide rows are the soil you hill with.
4. Set the tubers shoots upwards, 30 cm (12 in) apart for earlies, 37–40 cm (15–16 in) for maincrops. Handle chitted tubers gently — a snapped shoot costs a week.
5. Cover with 10–15 cm (4–6 in) of soil, or 8–10 cm (3–4 in) in cold heavy clay, where the tuber reaches warmth sooner and you add the rest when you hill.
6. Water only if the soil is genuinely dry. Cold wet soil around a new tuber is the commonest cause of rot.
7. Label the rows and wait. Emergence takes two to four weeks. Hoe shallowly meanwhile, but not where the tubers sit.

How much seed do you need?

Allow 0.2–0.3 kg of seed per m². A 10 m (33 ft) row at 30 cm spacing takes roughly 1.5–1.8 kg (3–4 lb) of seed. For a household wanting potatoes into winter, 40–60 m² is a realistic target.

Hilling: why, when and how much

Hilling — drawing soil into a ridge along the row, also called earthing up — is the only real labour in a potato crop, and it does four jobs at once.

• Keeps light off the tubers. A tuber exposed to daylight makes chlorophyll and turns green, and solanine rises with it.
• Makes room for more tubers. Tubers form on stolons off the stem above the seed piece, so more soil means more space.
• Cuts tuber infection. Blight spores wash off the leaves in rain; a tall steep ridge sheds that water sideways.
• Suppresses weeds. After the second hilling the canopy shades the ground itself.

Hill first when the shoots are 20–25 cm (8–10 in) tall, drawing soil up from both sides until only the top 10 cm (4 in) shows. The buried leaves are not harmed; the stem roots and throws new stolons.

Hill again two to three weeks later, when the foliage again stands 20–25 cm above the ridge. By then it should be 20–30 cm (8–12 in) tall with steep sides. On light soil that erodes in heavy rain, a third light hilling is cheap insurance.

Work when the soil is moist but not wet: bone-dry soil slumps back, saturated soil sets into clods. Stop once flowering begins, or you tear the roots. If you planted at a full 15 cm (6 in) one light hilling will do, but deep planting into cold soil delays emergence — hilling gets you both a fast start and deep tubers.

Watering, feeding and weeds

Watering

Potatoes are surprisingly drought-tolerant, but watering at the right moment pays for itself several times over. The critical window is the four weeks from tuber initiation — roughly bud stage to a week after flowering ends. Let the soil dry out then and you get fewer, smaller tubers and more scab, since the scab organisms attack while tubers are under 2 cm (3/4 in) across.

Allow 25 mm (1 in) per week through that window, rainfall included. Water deeply and less often: one soaking reaching 25 cm (10 in) down beats a daily sprinkle. Water at soil level early in the day — wet leaves overnight are exactly what blight needs. Ease off after flowering.

Feeding

Potatoes react badly to excess nitrogen. An overfed crop produces waist-high dark green foliage, late tuber set, soft watery potatoes and poor keeping quality.

• At planting: well-rotted compost, about 5 litres per m², worked into the bed rather than laid against the tuber.
• At the first hilling: a modest potassium-rich top-up on poor soil. Potassium builds tubers and firms the skin, and potato demand for it is high relative to nitrogen.
• After flowering: nothing. Late nitrogen keeps the foliage alive past its time and leaves a skin that never sets.

Wood ash is high in potassium but raises pH sharply, which favours scab. Spread it elsewhere.

Weeds

The first six weeks decide it; after that the canopy takes over. Hoe shallowly between rows until the first hilling and let the hilling do the rest. Perennial grasses such as couch grass must go before planting — they grow straight through a ridge.

Potatoes in raised beds, grow bags and under straw

Raised beds

A 120 × 80 cm (4 × 2.5 ft) raised bed holds six to eight tubers. Fill it a third full, set the tubers, cover with 8 cm (3 in), then keep adding soil as the foliage grows — hilling in vertical form. The soil warms earlier, buying about two weeks; the trade-off is that it dries out faster and needs watering in midsummer.

Grow bags and buckets

Allow at least 40 litres (10 US gal) per plant, ideally 60. Put 15 cm (6 in) of soil in the bottom, set two or three tubers in a 60-litre bag, cover with 10 cm (4 in) and top up as growth allows. Drill generous drainage holes in a bucket. Expect 1–2 kg (2–4 lb) per bag — less per plant than open ground, but it works on a balcony. Water daily in midsummer and feed fortnightly.

Potatoes under straw

Set the tubers in a shallow trench and cover with 20–30 cm (8–12 in) of straw, topping it up instead of hilling. Harvest is then a matter of pulling the straw aside and picking clean tubers by hand. Two caveats: the straw must stay thick, or light gaps turn tubers green, and it is excellent cover for slugs.

Late blight and tuber rot — spotting it and stopping it in time

Late blight is caused by the oomycete Phytophthora infestans, the same organism behind brown tuber rot and blight on tomatoes. It decides how your potato season ends, and in a maritime cold climate it turns up most years.

When does it arrive?

Usually from midsummer onwards. The pathogen needs long periods of leaf wetness and cool to mild temperatures — around 10–15 °C (50–59 °F) with dew or rain is ideal for spore production. A wet, cool July followed by mild humid weather in August is the standard recipe for a heavy outbreak. Infection comes from tubers left in the ground over winter, from compost heaps holding potato waste, and on the wind.

What to look for

• Leaves: dark olive to brown-black patches, often from the leaf margin inwards, with no sharp boundary against healthy tissue.
• Leaf undersides: a fine greyish-white fringe around the patch on a humid morning. That halo is the reliable identifier.
• Stems: dark brown continuous streaks that snap the shoot.
• Tubers: irregular sunken grey-brown patches, and beneath them a rust-brown dry rot spreading unevenly inwards.

What to do, and when

Home gardeners have no effective fungicide. What works is prevention: earlies lifted before the outbreak, resistant varieties, an open site, generous row spacing, tall ridges and a rotation that leaves no volunteer tubers behind.

The same pathogen attacks tomatoes and travels both ways, so keep the two crops at opposite ends of the garden — more on that in the guide to how to grow tomatoes.

When and how do you harvest potatoes?

New potatoes

First earlies are ready at about flowering, or as the buds open. Flowering and tuber size are only loosely linked, but it is the simplest signal the garden offers. Scrape the soil from one side of a plant and feel: hen's-egg size means start digging, smaller means put the soil back for a week. The skin should rub off under your thumb — that is what defines a true new potato, and why they keep only days. Lift one plant at a time.

Storage potatoes

Maincrops stand until the foliage dies back on its own. Tuber growth stops then, and the last weeks go into setting a firm skin — which is what makes storage work.

1. Cut the foliage once it has mostly yellowed, or earlier if blight arrives. Carry it off the plot.
2. Wait two to three weeks while the skin corks over. A skin you cannot rub off with your thumb is ready.
3. Choose a dry day, ideally after several dry days.
4. Dig with a fork, not a spade. Drive it in 25–30 cm (10–12 in) out from the plant and lift the whole ridge. A spade cuts straight through tubers.
5. Let them dry one to two hours on the surface or under cover — no longer, and never in direct sun, or they green up.
6. Sort immediately. Damaged, green and blemished tubers go to one side and get eaten first — never into the store.
7. Cure for 10–14 days at 10–15 °C (50–60 °F) in high humidity and darkness, so minor wounds heal and the skin hardens. Then drop to storage temperature.
8. Brush the soil off dry. Never wash potatoes for storage.

Finally, go over the rows again and pick up even the smallest tubers. Every one left behind overwinters as a blight source and a weed in the following crop.

How many potatoes do you get per square metre?

One kilo of seed returns six to ten kilos of crop in normal conditions — roughly 2–3 kg per m² in a well-managed garden, and 0.5–1.5 kg (1–3 lb) per plant depending on variety and season.

Working backwards: an adult who eats potatoes regularly gets through 40–50 kg a year, needing about 20 m² per person at a good yield. Most gardeners aim instead for new potatoes through summer plus a storage crop for winter, which fits into 30–50 m². Three things move the yield most: how long the foliage stays healthy, how evenly moist the soil is during bulking, and how much soil sits along the stem.

Crop rotation: how often can potatoes go in the same bed?

Leave at least three to four years between potato crops on the same ground. The serious problems are soil-borne and long-lived: cyst nematode, black scurf, blackleg and dormant blight in volunteer tubers. Count every nightshade in that gap — tomatoes, peppers and aubergines share several diseases with potatoes.

• Good before potatoes: a green manure, peas or beans, or rested ground. The nitrogen left by legumes goes a long way and the soil is already loosened.
• Good after potatoes: brassicas, onions and root crops. Potatoes leave an unusually weed-free, loose bed behind, thanks to the hilling and dense canopy. That suits how to grow carrots, which otherwise demand a lot of early hand weeding.
• Avoid straight after potatoes: tomatoes and other nightshades.

In a small garden a four-year gap is hard to hold. Split the ground into four, move the potatoes around them, and buy certified seed every year — far better than the same row twice running. The same logic applies to how to grow garlic, which should not return to the same bed too quickly either.

Common mistakes

• Planting supermarket potatoes. Untested, often sprout-inhibited, and a route for virus and nematodes into your soil.
• Planting too early into cold ground. Below 7 °C (45 °F) nothing happens but rot risk. Measure the soil, not the calendar.
• Hilling too little or too late. Green tubers and a light crop share this cause. Hill first at 20–25 cm (8–10 in) of growth.
• Fresh manure in the furrow. Rank foliage, soft tubers, more scab, poor storage. Use well-rotted compost worked into the bed.
• Liming the year before potatoes. Raises pH and increases scab. Potatoes want the more acid end of the garden.
• Skimping on water during flowering. Those four weeks are when irrigation genuinely pays.
• Digging too soon after cutting the foliage. Without two to three weeks the skin never sets.
• Washing potatoes for storage. Moisture on the skin plus storage equals rot.
• Leaving tubers in the ground. They overwinter, sprout and become the starting point for next season's blight.

Frequently asked questions

When should you plant potatoes?
Once soil at 10 cm (4 in) reaches 7 °C (45 °F), usually two to three weeks before your average last frost. That is mid to late April in USDA zone 6, early May in zone 5, mid to late May in zone 4 and early June in zone 3. Chitted seed goes in at the earlier end. Cover emerging shoots if frost threatens.

How deep should you plant potatoes?
10–15 cm (4–6 in) to the top of the tuber is standard. In cold heavy clay early in spring, 8–10 cm (3–4 in) is better: the tuber reaches warmth sooner and is less likely to rot. Whatever depth you leave out, you add back by hilling — so plant shallow and you must hill carefully, or the tubers turn green.

How far apart should potatoes be planted?
Earlies go 30 cm (12 in) apart in rows 60 cm (24 in) apart; maincrops need 37–40 cm (15–16 in) in rows 75 cm (30 in) apart. The wide rows give you the soil for tall ridges, and the air movement lowers blight pressure considerably. Closer spacing gives more, smaller tubers.

Do potatoes need to be chitted?
No, but it brings the crop forward two to three weeks, which matters in a short season. Stand the tubers rose end up somewhere bright, cool and frost-free at 10–15 °C (50–60 °F) for four to six weeks before planting. Aim for short, stubby shoots no more than 2 cm (3/4 in). In USDA zones 3 and 4 it is effectively necessary.

How many times should you hill potatoes?
Twice, sometimes three times. Hill first when the shoots are 20–25 cm (8–10 in) tall, then again two to three weeks later; a third light hilling helps on soil that erodes. Stop once flowering begins, or you tear the roots. The finished ridge should stand 20–30 cm (8–12 in) tall with steep sides.

When can you start digging new potatoes?
At about flowering, roughly ten to twelve weeks after planting a chitted first early. Scrape the soil from one side of a plant and feel: hen's-egg sized tubers mean it is time, smaller ones mean you cover them up for a week. The skin should rub off under your thumb. Lift as needed and cook the same day.

Why do potatoes turn green and can you eat them?
Greening is chlorophyll formed after exposure to light, and it develops alongside rising solanine, which is bitter and toxic in quantity. Cut away every green part generously, and discard the tuber if more than a third is green or it tastes bitter. Hill higher and replace soil washed off by heavy rain.

How long do home-grown potatoes keep?
A ripe maincrop with a set skin keeps from October into March or longer at 4–6 °C (40–43 °F), dark and at high humidity. Below 4 °C they turn sweet and fry dark. Store in wooden crates, paper sacks or perforated bins, never sealed plastic. New potatoes do not store and should be eaten within days.

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