Potato

A versatile tuber crop grown by hilling soil around the stems to encourage more tuber formation underground. Plant certified seed potatoes in trenches and mound soil progressively as shoots emerge to keep developing tubers shielded from light. Green-skinned tubers contain solanine and should not be eaten, so consistent hilling is essential throughout the season. Harvest new potatoes early for thin-skinned delicacies or wait until foliage dies back for mature storage potatoes.

Potatoes are grown from seed potatoes — tuber pieces with growth buds called 'eyes' — not from true botanical seed. Always purchase certified disease-free seed potatoes from a reputable garden supplier. Never plant grocery store potatoes: they may carry viruses, bacterial diseases, or have been treated with sprout inhibitors that prevent growth. Order seed potatoes 2-4 weeks before your intended planting date to allow time for chitting.

Chitting (pre-sprouting) gives potatoes a significant head start, especially in short-season climates. Place seed potatoes in a single layer in a bright, cool (10-15°C / 50-60°F) location with the end containing the most eyes facing upward. Over 2-4 weeks, sturdy 1-2 cm green or purple sprouts will develop. These sprouted potatoes establish faster and produce earlier harvests — particularly valuable in zones 3-5 where the growing season is limited.

Cut larger seed potatoes into pieces weighing at least 40-50g with 2-3 eyes each. Allow cut surfaces to dry and callus for 24-48 hours in a warm, dry place before planting — this creates a protective barrier against soil-borne rot organisms. Small seed potatoes (egg-sized, approximately 50g) should be planted whole. Plant pieces 10-15 cm (4-6 inches) deep and 30 cm apart in trenches, with eyes and sprouts facing upward, as soon as soil reaches 7°C (45°F). In most temperate climates, this means planting 2-4 weeks before the last frost date — potato shoots tolerate light frost and will regrow if nipped. For the longest harvest window, plant early, mid-season, and late varieties together.

Potatoes thrive in cool weather and are among the first crops planted in spring, as soon as soil is workable and temperatures reach 7-10°C (45-50°F). Begin by purchasing certified disease-free seed potatoes rather than grocery store tubers, which may carry viruses or have been treated with sprout inhibitors. Cut larger seed potatoes into pieces with 2-3 eyes each, allowing cut surfaces to dry and callus for 1-2 days before planting to prevent rotting. Plant pieces 10-15 cm (4-6 inches) deep and 30 cm apart in trenches or individual holes with eyes facing upward.

The key technique for growing potatoes is hilling — as shoots emerge and grow to 15-20 cm tall, mound soil, straw, or compost around the stems, leaving only the top few leaves exposed. This encourages more tubers to form along the buried stem and prevents tubers near the surface from turning green with toxic solanine. Repeat hilling 2-3 times during the growing season, eventually creating mounds 30-40 cm tall. Alternatively, grow potatoes in straw mulch, grow bags, or towers for easy harvesting.

Water consistently with 2.5-5 cm per week, especially during flowering when tuber formation is most active. Irregular watering causes knobby, cracked, or hollow tubers. Mulch between rows with straw to keep soil cool, retain moisture, and suppress weeds. Stop watering when foliage begins to yellow and die back naturally — this signals tubers are maturing and curing their skins for storage.

Beans fix nitrogen that potatoes can use, and their root structures don't compete. Marigolds deter Colorado potato beetles through their pungent volatile oils. Garlic and horseradish planted nearby repel many potato pests with their strong sulfur compounds. Avoid planting near tomatoes, peppers, and eggplant — all are nightshades sharing diseases like late blight and pests like Colorado potato beetle, so proximity concentrates pest and disease pressure. Cucumbers and squash also make poor neighbors as they compete aggressively for soil nutrients.

Potatoes thrive in loose, well-drained, slightly acidic soil with a pH of 5.0-6.0 — maintaining acidity is important because the common scab pathogen (Streptomyces scabies) thrives in alkaline conditions above pH 5.5. If your soil is above 6.0, avoid adding lime to potato beds and consider amending with sulfur to lower pH. Work 8-10 cm of aged compost or well-rotted manure into beds several weeks before planting. Avoid fresh manure, which can burn seed pieces, introduce pathogens, and promote scab.

Apply a balanced fertilizer (10-10-10 or 5-10-10) at planting time, placing it in the trench bottom below the seed piece to avoid direct contact. Side-dress with a nitrogen source (blood meal, fish emulsion, or ammonium sulfate) when plants reach 15 cm tall and again during hilling. Potassium is especially critical for potato quality — it improves tuber size, skin quality, storage life, and resistance to bruising. Incorporate greensand, sulfate of potash, or wood ash (sparingly, as ash raises pH) into beds before planting.

Avoid excessive nitrogen in the second half of the growing season — it promotes lush foliage at the expense of tuber bulking, delays maturity, and can reduce storage quality. Once flowering begins, stop nitrogen applications entirely and let the plant focus on tuber development. In heavy clay soils, grow potatoes in raised beds, grow bags, or thick straw mulch (the Ruth Stout method) for better drainage, easier hilling, and cleaner harvest. After harvest, plant a nitrogen-fixing cover crop (crimson clover, winter peas) to replenish the soil for next year's rotation.

Ideal Temperature

Hardiness Zone Compatibility

Potatoes offer two distinct harvest opportunities: new potatoes and mature storage potatoes. For new potatoes — small, thin-skinned baby tubers with delicate, creamy flesh — harvest 2-3 weeks after flowering begins. Carefully reach into the soil near the plant base and feel for egg-sized tubers, removing only a few without disturbing the main root system. New potatoes don't store well but their fresh, sweet flavor is a garden luxury unavailable in stores.

For mature storage potatoes, patience pays off. Wait until the foliage has completely yellowed and died back naturally — this signals that the plant has stopped growing and is redirecting energy into tuber maturation. After foliage death, wait an additional 2 weeks with tubers still in the ground for the skins to thicken and cure, which dramatically improves storage life. If late blight threatens, cut all foliage to ground level and wait 2 weeks before digging to prevent spores from infecting tubers.

Harvest on a dry day using a garden fork inserted at least 30 cm from the plant stem to avoid spearing tubers — speared potatoes must be eaten immediately as they won't store. Work carefully through the hill, lifting and sifting soil to find all tubers, including those that have wandered. Let freshly dug tubers air-dry on the soil surface for 1-2 hours (avoid direct sun, which causes greening), then brush off loose soil without washing. Cure storage potatoes in a dark, well-ventilated space at 10-15°C (50-60°F) and 85-90% humidity for 10-14 days — this heals skin wounds and converts sugars back to starch for optimal flavor. Handle gently throughout — bruised potatoes develop black spots internally and rot quickly in storage.

Storage & Preservation

Properly cured potatoes are among the longest-storing garden vegetables — under ideal conditions they'll keep 4-6 months or even longer. The perfect storage environment is dark, cool (4-7°C / 40-45°F), humid (85-90%), and well-ventilated. A root cellar is traditional; an unheated garage, cool basement, or insulated outdoor pit also works. Store in burlap sacks, paper bags, or ventilated crates — never sealed plastic, which traps moisture and promotes rot. Keep potatoes away from apples, which emit ethylene gas that causes premature sprouting.

Never refrigerate raw potatoes — temperatures below 4°C (39°F) convert starch to sugar, causing an unpleasant sweet taste and dark discoloration when fried or roasted. If sprouts develop on stored potatoes, simply break them off — the potato is still fine to eat as long as the flesh is firm. Check stored potatoes monthly and immediately remove any showing soft spots, mold, or strong odor before they affect their neighbors.

For freezing, potatoes must be cooked first — raw frozen potatoes turn gray and grainy. Blanch cubes or slices for 3-5 minutes, cool, and freeze on sheet pans before bagging. Mashed potatoes freeze beautifully in portion-sized containers with a bit of butter and cream mixed in. French fries can be par-fried, frozen on trays, and finished later. Pressure canning (not water-bath — potatoes are low-acid) preserves cubed potatoes at 10 PSI for 35 minutes (pint jars) or 40 minutes (quarts). Dehydrating is excellent for long-term storage: blanch thin slices and dry at 52°C (125°F) for 8-12 hours until brittle — they rehydrate well for hash browns, gratins, and soups.

Troubleshooting Common Problems

Green-skinned potatoes are the most common issue and result from tubers being exposed to light — solanine, the toxic compound responsible for the green color, develops rapidly in sunlight. Prevent greening by hilling soil around plants consistently as they grow and mulching heavily with straw. If you find green-skinned tubers at harvest, the green portions (and about 1 cm below) should be cut away before eating; lightly greened potatoes are safe once trimmed. Deeply green potatoes should be discarded entirely.

Hollow heart — a star-shaped cavity inside otherwise normal-looking large tubers — results from rapid, uneven growth caused by inconsistent watering or a sudden flush of nitrogen after a dry period. Prevention is straightforward: maintain consistent, moderate moisture and avoid heavy fertilizer applications after tuber initiation begins. Cracked or knobby, misshapen tubers also indicate irregular watering during the critical tuber development phase.

If plants grow tall with abundant dark-green foliage but produce few or small tubers, excessive nitrogen is almost certainly the cause — the plant is investing in leaves instead of tubers. Reduce nitrogen and ensure adequate potassium, which directs energy toward tuber formation. Poor yields with small tubers can also result from overcrowding (plant 30 cm apart minimum), insufficient hilling, or growing in compacted soil that physically restricts tuber expansion. Internal black spot — dark bruise marks inside the flesh — is caused by rough handling during and after harvest; always handle potatoes as gently as eggs.

Growing Tips

1. Always buy certified disease-free seed potatoes — never plant grocery store potatoes, which carry diseases and may have been treated with sprout inhibitors.
2. Chit (pre-sprout) seed potatoes for 2-4 weeks in bright, cool conditions before planting. This gives a 2-3 week head start and is essential in short-season climates.
3. Hill aggressively and often — mound soil around stems when shoots reach 15-20 cm, leaving only the top leaves exposed. Repeat 2-3 times during the season. More hilling = more tubers.
4. Maintain soil acidity below pH 5.5 to suppress common scab — avoid liming potato beds. Use sulfur amendments if your soil is too alkaline.
5. Water consistently during tuber bulking (flowering onward) — this is when tuber size is determined. Irregular watering causes hollow heart, cracking, and knobby tubers.
6. Stop watering and stop fertilizing when foliage begins to yellow. Leave tubers in ground for 2 weeks after foliage dies to cure skins — this dramatically improves storage life.
7. Rotate potatoes on a strict 3-year cycle and never follow other nightshades (tomatoes, peppers, eggplant). Late blight, Verticillium wilt, and Colorado potato beetle all build up in soil.
8. Grow in bags, towers, or straw mulch if your soil is heavy clay — this makes hilling easy and harvest effortless. Simply pull back the straw or dump the bag to collect clean tubers.