Potatoes are one of the world’s most common and adaptable food crops, yet a successful harvest relies heavily on proper timing. The edible part of the plant is a tuber, an underground storage stem that develops from a specially prepared piece of potato called a “seed potato.” These seed potatoes are small tubers, or pieces of tubers, used for vegetative propagation. Understanding the precise window for planting is paramount because it dictates whether the crop will mature before the heat of summer or the first killing frost of autumn.
Preparing Seed Potatoes Before Planting
The planting timeline begins weeks before the seed potatoes go into the soil. A process called “chitting,” or pre-sprouting, is often employed to give the plants a head start, especially for early varieties. This involves placing the seed potatoes in a cool, bright, and frost-free location for four to six weeks before planting. The light exposure encourages the potato “eyes” to form short, thick, dark-colored sprouts rather than the long, pale, brittle ones that form in the dark.
The presence of these sturdy sprouts speeds up the growth cycle once the seed potato is placed underground, leading to an earlier harvest. Larger seed potatoes, those bigger than a chicken egg, should be cut into pieces roughly the size of a golf ball, ensuring each piece has at least one or two eyes. After cutting, let the pieces “cure” for a few days to allow the cut surface to dry and form a protective layer, which helps prevent rot when planted in cool, moist soil.
Finding the Ideal Planting Window
The most direct answer to when to plant potatoes depends on local environmental factors, specifically the last expected hard frost and the soil temperature. Potatoes are a cool-season crop; they can tolerate a light frost on their foliage, but a hard freeze can be damaging. Gardeners generally aim to plant two to four weeks before the average last frost date for their region to maximize the growing season.
Soil temperature is a more accurate indicator than the calendar, as potatoes will not begin to grow until the soil warms sufficiently. The minimum soil temperature required for planting is approximately 45°F (7°C). Ideally, planting occurs when the soil is consistently in the range of 45°F to 55°F (7°C to 13°C). Planting in soil that is too cold or waterlogged significantly increases the risk of the seed pieces rotting before they can sprout.
To determine the correct time, use a soil thermometer to check the temperature at a depth of about four inches, ideally in the morning. In warmer southern climates, this window may open as early as late winter, while in northern regions, it may not arrive until late spring. Planting too late, when the soil temperature exceeds 80°F, can inhibit tuber development.
Timing Based on Desired Harvest
The ideal planting date is governed by the specific type of potato being grown and the desired harvest time. Potato varieties are categorized mainly as “earlies” or “maincrops,” a distinction based on their time to maturity. Early varieties, which include first and second earlies, are often referred to as “new potatoes” because they are harvested young, producing small, thin-skinned tubers.
First early varieties have the shortest growing period, often ready for harvest in 55 to 70 days after planting, while second earlies take slightly longer, around 70 to 90 days. These early types are typically planted first, as soon as the soil is warm enough, to get a mid-summer crop and can be harvested before the season’s peak disease pressure. Maincrop varieties require a much longer time to reach full maturity, typically needing 90 to 120 days or more.
These longer-season potatoes produce the large, thick-skinned tubers best suited for long-term storage over the winter months. Maincrop potatoes are usually planted a few weeks later than the earlies to utilize the full growing season and ensure the tubers have enough time to bulk up. Choosing a variety with a shorter maturity window allows planting to occur later, which is useful in areas with a short growing season or to avoid a late spring frost.
Post-Planting Timeline and Care
Once the seed potatoes are planted, the timeline shifts to maintenance tasks that ensure a bountiful harvest. The first significant task is “hilling,” which involves drawing up soil around the emerging green shoots. This process should begin when the stems are about six to eight inches tall and is repeated every few weeks as the plant grows.
Hilling serves two purposes: it protects the developing tubers from sunlight, preventing them from turning green and toxic, and it encourages the formation of more underground stems, or stolons, where new potatoes develop. Consistent moisture is necessary throughout the growing season, especially from the time the plants begin to flower, which signals that the tubers are starting to form. Potatoes require about one inch of water per week during the tuber development and bulking stages.
The final stage of the timeline is signaled by the plant itself; harvest is ready when the foliage, or vines, turn yellow and begin to die back. For new potatoes, a small harvest can be dug about seven to eight weeks after planting, often shortly after the plant flowers. For the maincrop, mature tubers are typically ready for digging about two weeks after the tops have completely died down, allowing the skin to set for better storage.