Potatoes thrive in Maine’s cool climate and rich, often acidic soils. Successful growth hinges on precise timing. Planting too early risks rot in cold soil, while planting too late exposes plants to summer heat stress. The goal is to maximize the cool, moist period of spring and early summer for tuber development. Achieving a strong harvest requires monitoring local climate indicators and following specific preparation techniques tailored to Maine’s variable geography.
Determining the Ideal Planting Window
The calendar date is less reliable for planting than the soil temperature and the threat of the last hard frost. Potatoes are a cool-season crop that tolerates light frost, but seed pieces will rot if planted into cold, waterlogged soil. The optimal time for planting is approximately two to four weeks before the average last expected hard frost date for your region, provided the soil is workable.
The most accurate metric is the soil temperature, which should consistently register at least 45°F at a four-inch depth. Maine’s diverse geography means this window varies significantly. Coastal areas warm up earlier, often allowing planting in late April to early May. Inland and northern regions may not reach this critical temperature until late May or early June, making local knowledge or county extension data indispensable. Planting into soil below 45°F increases the risk of seed piece decay; the 45°F to 50°F range promotes successful sprouting.
Preparing Seed Potatoes and Soil
Before planting, seed potatoes require “chitting,” which encourages the development of short, sturdy sprouts. This involves placing them in a single layer in a warm, well-lit location for two to three weeks until small, green sprouts emerge. This pre-sprouting gives the seed a head start, shortening the time until the plant emerges from the soil.
Larger seed potatoes should be cut into blocky pieces, weighing 1.5 to 2.5 ounces. Ensure each piece contains at least one, but preferably two, healthy “eyes.” After cutting, allow the pieces to dry and cure for two to three days at room temperature. This forms a protective layer over the cut surface to prevent disease and rot. Potato plants prefer a slightly acidic soil pH, ideally between 5.5 and 6.0, which helps suppress the common potato scab disease.
Planting Depth and Spacing
When the soil temperature is adequate, plant the prepared seed pieces at a depth of four to six inches. This depth provides sufficient soil cover, which is the foundation for the subsequent hilling process. If planted too shallowly, developing tubers will be exposed to sunlight, causing them to turn green and produce the toxic compound solanine.
The pieces should be spaced about 12 inches apart within the row to give each plant room to form a cluster of tubers. Rows should be separated by two and a half to three feet. This generous spacing ensures adequate room for light penetration, air circulation, and the necessary soil hilling as the plants mature.
Early Season Hilling and Care
The first hilling begins once the emerging potato plants reach a height of six to eight inches. Hilling involves pulling loose soil up from between the rows and mounding it around the base of the stems, creating a protective ridge. This shields the newly forming tubers from light and provides a barrier against unexpected late spring frosts.
Hilling should be repeated as the plants grow, typically every one to two weeks, until the plants begin to flower. Each subsequent hilling should cover all but the top few inches of the foliage, continually adding soil to ensure the developing tubers remain buried. Consistent moisture is also important during this early growth phase. Potatoes require about one inch of water per week from rain or irrigation, as inconsistent watering can lead to misshapen tubers.