Growing Potatoes

Always plant certified seed potatoes, not grocery store potatoes. Certified seed is inspected for viral diseases (PVY, PLRV, mosaic viruses) that reduce yield by 30-50% over successive generations. Grocery store potatoes may carry these diseases and are often treated with sprout inhibitors.

Order seed potatoes 2-4 weeks before planting. Small seed potatoes (1-2 oz) can be planted whole. Larger ones should be cut into pieces with 2-3 eyes each, cut-side allowed to callus for 1-2 days before planting. Each seed piece produces one plant. You need approximately 10-15 lbs of seed potatoes per 100-foot row.

Potatoes prefer loose, well-drained, slightly acidic soil (pH 5.0-6.0). Higher pH increases the risk of scab disease. Do not lime potato beds in the year before planting. Incorporate 2-3 inches of compost before planting. Avoid fresh manure - it promotes scab and can cause hollow heart in tubers.

Plant 2-4 weeks before the last frost date (potatoes tolerate light frost; the foliage will be damaged but regrows from the tuber). Dig trenches 4-6 inches deep, space seed pieces 12 inches apart in rows 30-36 inches apart. Cover with 3-4 inches of soil. As shoots emerge and grow to 6-8 inches, begin hilling - this is the key technique in potato growing.

Potatoes form tubers on stolons (underground stems) above the seed piece. Hilling - mounding soil, straw, or compost around the growing stems - gives tubers more space to develop and prevents them from being exposed to sunlight (which turns tubers green and toxic from solanine).

Hill when plants are 6-8 inches tall: pull soil from between the rows up around the stems, leaving only the top 3-4 inches of foliage exposed. Repeat 2-3 times as the plant grows. Each hilling adds 3-4 inches of soil. The final hill should be 8-12 inches tall. Alternative methods: plant in deep mulch (12+ inches of straw layered on as the plant grows) or grow in fabric bags/towers where you add soil as the plant grows upward.

Consistent moisture is critical during tuber initiation (when flowers appear) and tuber bulking (2-4 weeks after flowering). Water stress during these stages causes knobby, misshapen tubers and reduces overall yield. Provide 1-2 inches per week through drip irrigation or soaker hoses. Stop watering 2 weeks before harvest to let skins toughen.

Potatoes need moderate nitrogen (too much promotes foliage at the expense of tubers), adequate phosphorus (for root and tuber development), and high potassium (for tuber size and quality). Apply a balanced organic fertilizer or 10-20-20 at planting, and side-dress with potassium-rich fertilizer (sulfate of potash, wood ash) at first hilling. Avoid high-nitrogen feeds after flowering.

Colorado Potato Beetle (CPB) is the #1 insect pest - orange-and-black striped adults and red larvae defoliate plants rapidly. Hand-pick adults and crush orange egg masses on leaf undersides. Apply Bt (Bt tenebrionis strain, marketed as BtSD) for larvae, or spinosad for heavy infestations. Rotate potato location annually - CPB overwinters in soil near previous plantings.

Late Blight (Phytophthora infestans - the disease that caused the Irish Potato Famine) appears as dark water-soaked spots on leaves during cool, wet weather. It can destroy a field in days. Preventive copper sprays during wet periods, resistant varieties (Sarpo Mira, Defender), good air circulation, and avoiding overhead irrigation are the primary defenses. Destroy infected plants immediately - do not compost them.

New potatoes (small, thin-skinned) can be harvested as soon as plants flower - gently dig around the base and take a few tubers while leaving the plant to keep growing. Main crop harvest happens when foliage dies back naturally (or you cut it 2 weeks before harvest to toughen skins). Dig carefully with a garden fork, working from the outside of the hill inward to avoid spearing tubers.

Cure main crop potatoes by leaving them in a dark, dry, well-ventilated area at 50-60°F for 1-2 weeks. This heals skin wounds and converts sugars to starch for better storage. After curing, store at 38-45°F with 90% humidity and complete darkness. Properly stored, late-season potatoes last 4-6 months. Never store potatoes near apples - ethylene gas from apples causes premature sprouting.