The potato is a tuber crop, an enlarged underground stem. Maximizing yield requires precise timing for planting to avoid spring frost damage and ensure a sufficiently long cool growing season. Across Indiana, the ideal planting window shifts significantly, making a geographical approach essential for a successful harvest.
Optimal Planting Time Across Indiana Regions
The primary factor determining the best planting time is the soil temperature, which should consistently reach 45 to 50 degrees Fahrenheit. Planting too early into cold, soggy soil risks the seed piece rotting before it can sprout. Potatoes are a cool-season crop that can tolerate a light frost, making the window approximately two to four weeks before the average last spring frost date.
Southern Indiana, which experiences warmer soil temperatures first, allows for the earliest planting, typically from late March through mid-April. Moving north into Central Indiana, including the Indianapolis area, the planting window shifts to mid-April through the first week of May. Gardeners in Northern Indiana should wait until late April or early May, as the ground remains cooler longer. Planting must occur early enough to allow tubers to develop fully before the intense heat of summer begins, which can halt tuber formation.
Preparing Seed Potatoes and Soil
Before planting, use certified, disease-free seed potatoes rather than grocery store varieties, which are often treated with sprout inhibitors. For larger seed potatoes, cut them into pieces weighing about 1.5 to 2 ounces, ensuring each piece contains at least one or two “eyes” (the buds from which the new plant will grow). After cutting, allow the pieces to cure for a day or two in a warm, humid environment to form a protective callous, which helps prevent rot in the soil.
This preparation can also include “chitting,” or green sprouting, where seed pieces are exposed to light and cool temperatures (around 50°F) for several weeks to develop short, sturdy sprouts. This process gives the plant a head start and can result in an earlier harvest. The soil should be loose, deep, and well-draining, as compacted or waterlogged soil causes misshapen tubers and rot. Potatoes thrive in slightly acidic soil, ideally with a pH between 5.8 and 6.5, which helps suppress the potato scab fungus.
Planting Depth and Hilling Techniques
Initial planting involves placing the seed potato pieces, with sprouts facing upward, into a trench or hole four to six inches deep. Spacing the seed pieces approximately 12 inches apart allows ample room for the plant to develop a strong root system and produce multiple tubers. Once covered with three to four inches of soil, the waiting period begins until the sprouts emerge.
The unique requirement for growing potatoes is “hilling,” the practice of mounding soil or organic matter around the growing stems. When plants reach six to eight inches tall, gently pull soil up around the stem, covering all but the top few leaves. This action encourages the development of more underground stems, called stolons, where new tubers form. Hilling must be repeated every two to three weeks as the plant grows, ultimately building a mound 10 to 12 inches tall. This prevents developing tubers from being exposed to sunlight. Tubers exposed to light turn green and produce solanine, a mild toxin that makes the potato inedible.
Understanding the Harvest Schedule
The time from planting to harvest depends on the variety chosen, ranging from 60 to 120 days. For “new potatoes,” which are small, thin-skinned, and best for immediate consumption, harvesting can begin two to three weeks after the plant has finished flowering. At this stage, the plant is still green and actively growing, so digging a few small tubers from the perimeter allows the rest to continue maturing.
For a mature, long-storing crop, wait until the plant’s foliage naturally yellows, withers, and dies back entirely (a process called senescence). This signal indicates the tubers have fully matured and their skins have thickened, or “set.” After the tops have died, allow the potatoes to remain in the ground for an additional two weeks to ensure the skins are fully cured for optimal storage potential.