Why Are My Potatoes Cracking and Splitting?

You dig up potatoes at harvest and find them split along their length, sometimes cracked right through. Or you notice cracking developing on tubers left in the ground as autumn rains arrive after a dry summer. Potato cracking is a very common problem in variable climates and is almost always caused by one thing: a sudden surge of water — from rain or irrigation — after a period of dry conditions. The potato skin hardens and becomes less elastic during a drought, then cannot expand fast enough when growth suddenly resumes.

The boom-and-bust growth cycle

When soil moisture is limited, potato tuber growth slows and the skin sets into whatever shape the tuber has reached. When water suddenly becomes abundant again — after heavy rainfall or resuming irrigation — the inner flesh expands rapidly. The skin, which has stiffened, cannot keep pace with this sudden expansion and cracks. The same mechanism causes cracking in tomatoes and many root vegetables. Cracks can be surface-level or deep enough to create a split right through the tuber. The flesh is perfectly edible but cracked potatoes store poorly because the wounds allow rot to enter.

Soil type and its role

Sandy, free-draining soils are most prone to causing cracking because they dry out very quickly during dry spells, then let water through rapidly during rain, creating exactly the stop-start moisture cycle that causes the problem. Heavy clay soils can also be problematic in the opposite way: they stay wet for long periods then crack dry themselves, with tubers in the cracks exposed to sudden moisture swings. Loamy, well-structured soil with good moisture retention stays more consistent through both wet and dry spells.

How to prevent cracking

The most effective prevention is consistent soil moisture throughout the growing season. Do not wait until the soil is very dry before watering — water regularly and deeply before stress sets in. Apply a 5–8 cm mulch of straw, compost, or other organic material around plants once they are well established. Mulch dramatically reduces evaporation from the soil surface and buffers the moisture swings that cause cracking. In a hot, dry summer, watering every five to seven days at 20 litres per square metre is a reasonable minimum — more often in very free-draining soil or during heat waves.

Harvesting cracked potatoes

Cracked potatoes should be harvested and used immediately — do not store them because the wounds provide entry points for fungal rot that will spread to neighbouring sound tubers in storage. Trim away cracked areas before using; the remaining flesh is perfectly fine. If you find cracking developing late in the season as autumn rains arrive, harvest the crop promptly rather than leaving tubers in the ground through wet weather. Newly cracked tubers are intact on the inside; tubers that have sat in wet soil with cracks for weeks may have developed internal rot that makes them inedible.