When to Plant Potatoes in Ontario — 2026 Guide

Chitting (pre-sprouting)

Chitting means placing seed potatoes in a cool, bright spot (10–15°C) to develop short, stubby sprouts before planting. Start chitting 3–4 weeks before your target planting date — late February to mid-March for most Ontario cities. Stand the potatoes rose-end up (the end with the most eyes) in an egg carton or shallow tray. Sprouts should be 1–2 cm when planted. Chitted potatoes establish faster, produce earlier harvests, and are less vulnerable to rotting in cold soil than unchitted potatoes.

Cutting large seed potatoes

Seed potatoes larger than a golf ball (over 60–70 g) should be cut into pieces, each with at least 2 eyes. After cutting, leave the pieces in a single layer at room temperature for 24–48 hours to let the cut surfaces callous over — this is called curing the cut. A calloused cut surface resists soil-borne rot. Plant cut pieces cut-side down. Small seed potatoes (egg-sized) can be planted whole and don't need cutting.

Soil temperature rule

Ontario's April soil is often still cold and wet after snowmelt, especially in Ottawa and Kingston. Seed potatoes planted below 7°C sit dormant and rot before sprouting. Use a soil thermometer at planting depth (10–15 cm). If the soil sticks to your shovel in clumps, it's too wet and likely still too cold — wait one more week. A late planting in warm soil always outperforms an early planting in cold soil.

🥔 Early Varieties (60–75 days) — New potatoes and all Ontario zones

🥔 Main Crop (80–110 days) — Toronto, Hamilton, Windsor

Colorado potato beetle — the #1 Ontario potato pest

Distinctive yellow-and-black-striped adult beetles; orange-red larvae with black spots; can defoliate plants within days. Two generations per year in Ontario. Control: hand-pick adults and larvae daily into soapy water (works for small plantings); remove orange egg masses from leaf undersides; floating row cover for the first 4 weeks until plants are too large; rotate to a new bed every year (beetles overwinter in soil where potatoes grew); Bt 'tenebrionis' spray works against larvae but not adults; resistant variety: Elba (some resistance). Heaviest pressure in Southwestern ON and Niagara; lighter in Northern Ontario.

Wireworm (click beetle larvae)

Yellow-brown thin worms that tunnel through tubers leaving small dark holes. Worst in beds recently converted from lawn or where green manure was tilled in. Control: beneficial nematodes (Heterorhabditis spp.) applied to soil in spring are highly effective; potato slice traps (bury slices to lure wireworms, dig and destroy daily); 2-year rotation away from grass-cover beds; avoid planting potatoes in newly broken sod for the first two years.

Common scab (Streptomyces scabies)

Brown corky lesions on tuber skin; cosmetic damage but reduces storage life and market value. Worst in alkaline soil and dry conditions during tuber formation. Control: never lime potato beds (potatoes prefer pH 5.0–6.0, slightly acidic); consistent moisture during tuber formation (weeks 6–10 after planting); avoid fresh manure; resistant varieties: Russet Burbank, Norland, Caribe, Kennebec. Crop rotation 3+ years away from potatoes, beets, and carrots.

Green tubers (sun exposure)

Green skin develops solanine, a mildly toxic alkaloid — never eat green potatoes. Caused by tubers being exposed to sunlight as they swell near the soil surface. Control: hill aggressively — mound soil around plants twice during the season to keep tubers buried 15+ cm deep. Cover any exposed tubers with extra soil or mulch as soon as you see them.

Hollow heart & growth cracks

Internal cavities (hollow heart) and external splits (growth cracks) result from drought followed by sudden heavy watering or rain — the tuber expands faster than its tissue can grow. Control: consistent moisture throughout the season (2–3 cm/week), especially during tuber formation in weeks 6–10; mulch heavily to even out moisture; avoid letting plants wilt then drowning them. Smaller varieties (Norland, Yukon Gold) less prone than huge bakers (Russet).

Soil preparation

Potatoes prefer loose, well-draining, slightly acidic soil (pH 5.5–6.5). Heavy clay soil common across much of Ontario — especially in Hamilton, London, and Ottawa — compacts around developing tubers and produces misshapen potatoes with thicker skins. Work in 7–10 cm of compost before planting to improve drainage and loosen texture. Avoid fresh manure — it promotes scab disease (rough, corky patches on the skin). Never lime potato beds — raising pH above 6.5 encourages common scab. Rotate potatoes to a new bed every 3 years minimum.

Watering

Consistent moisture is critical from flowering to harvest — this is when tubers are bulking and irregular watering causes hollow heart (empty centres) and knobby, misshapen tubers. Aim for 2.5 cm of water per week. Deep watering twice a week is better than daily shallow watering — deep moisture encourages roots to follow water down rather than staying near the surface. During Ontario's July heat, water more frequently. Reduce watering significantly once foliage begins to yellow and die back — excess moisture at this stage causes storage tubers to rot in the ground.

Fertilising

Apply a balanced fertiliser (10-10-10) or compost at planting. Potatoes need phosphorus for root and tuber development and potassium for yield and storage quality. Once plants are growing vigorously, switch to a low-nitrogen fertiliser — excess nitrogen produces lush foliage at the direct expense of tuber production. A common Ontario mistake is continuing to feed high-nitrogen fertiliser through summer, which results in beautiful plants with small, watery tubers underneath. Stop all fertilising once plants begin to flower — the plant's energy should go entirely into tuber bulking at this stage.

Choose resistant varieties

Kennebec and Defender are the most blight-resistant common varieties available in Ontario. Elba and Allegany offer good resistance for main-crop timing. Yukon Gold has moderate susceptibility — in a wet summer it benefits from preventive copper spray. Russet Burbank is susceptible and requires attentive monitoring. For Ottawa and Kingston gardens that experience wet conditions, blight-resistant variety choice is the single highest-impact decision you can make.

Cultural controls

Rotate potatoes (and all other Solanaceae — tomatoes, peppers) to a new area of the garden every 3 years minimum. Blight spores overwinter in soil and infected plant debris. Water at the base of plants only — wet foliage is the primary entry point for blight and early blight spread. Space plants 30 cm apart and rows at least 60 cm apart for airflow. Remove and bag (not compost) any foliage showing brown-black lesions with a white fuzzy border immediately. Never save seed potatoes from a blighted crop.

Copper fungicide — for wet Ontario summers

When Ontario's July brings extended wet periods (3+ consecutive days of rain), a preventive application of copper-based fungicide (Bordeaux mixture or copper hydroxide) applied to foliage every 7–10 days slows blight significantly. Apply before symptoms appear — copper is a protectant, not a curative. It's approved for organic use. If blight has already caused significant foliage loss, the practical strategy is to cut all foliage at ground level, wait 2 weeks for skins to cure in the soil, then harvest before the spores reach the tubers.

In-ground curing before digging

Once potato foliage dies back naturally, leave the tubers in the ground for 10–14 days before digging. During this time the skin sets and toughens, dramatically improving storage life. This step is skipped only if fall frost is imminent and the soil is about to freeze. For Ottawa and Kingston where the first frost can arrive by mid-October, monitor your foliage closely — begin the in-ground cure immediately when plants die back so you have the full 2 weeks before ground freeze.

Post-harvest curing

After digging, spread potatoes in a single layer in a dark, humid space at 10–15°C for 1–2 weeks. A garage or basement works well in September. This allows minor cuts and scrapes from digging to heal — unhealed wounds are the primary entry point for storage rot. Do not wash potatoes before curing or storing — dry soil on the skin is protective. After curing, brush off loose dirt gently and move to final storage.

Long-term storage

Store cured potatoes in a cool (4–7°C), dark, well-ventilated location. A cold cellar, unheated basement, or insulated garage through Ontario's winter are ideal. Never store near apples — apples release ethylene gas that causes potatoes to sprout faster. Check stored potatoes every few weeks and remove any that are softening or rotting before they infect neighbours. Kennebec and Russet Burbank store well for 4–6 months under proper conditions. Yukon Gold stores for 2–3 months. Fingerlings are best eaten within 6–8 weeks of harvest.

When should I plant potatoes in Ontario?

2–4 weeks before last frost when soil reaches 7°C: Toronto/Windsor April 1–15, Hamilton April 5–20, London April 10–20, Kingston April 20–May 1, Ottawa April 25–May 5. Potatoes tolerate light frost — the main risk is cold wet soil causing seed potatoes to rot before sprouting.

When do I harvest potatoes in Ontario?

New potatoes: when plants flower, usually July. Storage potatoes: when foliage dies back naturally, usually August–September. Leave in ground 2 weeks after die-back for skins to cure before digging. Harvest before the first fall frost hardens the ground.

Can I plant grocery store potatoes?

Not recommended — grocery store potatoes are often treated with sprouting inhibitors and may carry diseases. Always use certified seed potatoes from a garden centre or seed supplier. Certified seed potatoes are disease-tested and guaranteed to sprout. Available at Canadian Tire, Home Hardware, and most Ontario garden centres from March onward.

Why are my potatoes turning green?

Green potato skin and flesh contains solanine — a toxic compound produced when tubers are exposed to light. Prevention: hill consistently so no tubers are exposed, and store harvested potatoes in complete darkness. Do not eat any green potato parts — cut away and discard all green areas before cooking, or discard the potato entirely.

Why are my potatoes small or hollow inside?

Small tubers usually mean excess nitrogen — too much fertiliser pushes leafy growth at the expense of tubers. Hollow heart (empty core) is caused by irregular watering during the tuber-bulking stage after flowering. Both are prevented by switching to low-nitrogen fertiliser once plants are established and maintaining consistent deep watering through July and August.

Can I grow potatoes in containers in Ontario?

Yes — 40-litre containers or larger work well on Ontario decks and patios. Plant 2–3 seed potatoes per container, 15 cm deep. As plants grow, add potting mix to the top in place of hilling. Water consistently — containers dry out faster than beds. Harvest by dumping the container when foliage dies back. Container potatoes store for a shorter time — eat within a few weeks of harvest.