The success of a potato harvest is determined by timing, as planting too early or too late severely impacts both the quantity and quality of the yield. Potatoes are grown from specialized tubers called seed potatoes, which produce new plants. Precise planting ensures the growing period aligns with favorable weather, maximizing the development of underground tubers and helping to prevent common diseases like blight.
Pre-Planting Preparation
Before planting, “chitting” or pre-sprouting is beneficial, especially for early-season varieties, as it gives the seed potato a head start. Chitting involves placing the seed potatoes in a bright, cool, frost-free location for about four to six weeks before planting. This encourages the development of short, sturdy sprouts, ideally about a half-inch to an inch long, which accelerate the plant’s emergence once placed in the ground.
The planting location requires preparation to support the underground development of the tubers. Potatoes thrive in loose, well-drained soil, as compacted or waterlogged conditions can lead to misshapen tubers and increase the risk of rot. Working the soil deeply, to a depth of 12 to 18 inches, and incorporating organic matter, like compost, improves both drainage and fertility.
Determining the Optimal Planting Window
The earliest time to plant potatoes is governed by the risk of hard frost and the temperature of the soil. Potatoes are a cool-season crop, but their emerging foliage cannot tolerate a severe freeze, which can kill the top growth and delay the harvest. A general rule is to plant the seed potatoes about two to four weeks before the average date of the last expected spring frost.
The soil temperature provides the most accurate signal for a safe planting time. Potatoes should not be planted until the soil temperature consistently reaches a minimum of 40°F, as colder, wet soil increases the risk of the seed pieces rotting. The ideal range for quick sprouting is between 45°F and 50°F, which can be checked by inserting a soil thermometer six inches deep. Waiting for this soil warmth ensures rapid emergence and reduces the stress of cold conditions.
Timing Based on Potato Type
Planting schedules vary depending on the desired harvest time, which is categorized by the variety’s maturity rate. Early varieties, often called First Earlies, mature the fastest, typically within 70 to 90 days. They are planted earliest, often from mid-March to early April, and are harvested as “new potatoes” in early summer. These do not store well, making them ideal for immediate consumption.
Second Early varieties take about 14 to 16 weeks and are generally planted a couple of weeks after the First Earlies, from early to mid-April. This sequential planting extends the fresh potato harvest over several weeks. Maincrop or Late varieties require the longest growing season, maturing in 16 to 22 weeks, and are planted later, typically from mid-April to early May. These produce the largest tubers, which are best suited for baking, roasting, and long-term storage.
Post-Planting Care and Harvest Readiness
Once planted, the maintenance technique called hilling or earthing up is important for tuber development. Hilling involves gradually mounding soil up around the stems of the plant as they grow, beginning when the shoots are about 6 to 8 inches tall. This process covers the developing underground tubers, preventing them from being exposed to sunlight. Sunlight causes the tubers to turn green and produce a mildly toxic compound.
Consistent moisture is necessary, especially after the plant flowers when new tubers begin to bulk up. Potatoes generally require about one to two inches of water per week, and inconsistent watering can lead to growth defects like hollow heart. Harvest time is signaled by the plant’s foliage, or “haulms.” For maincrop varieties intended for storage, the foliage should be allowed to fully yellow and die back completely, indicating the tubers have reached full maturity and developed a thick, protective skin.