Potatoes are a staple crop successfully grown throughout Michigan, providing a rewarding harvest for local growers. Determining the precise moment to dig your potatoes, however, is not a matter of a fixed calendar date. The optimal harvest time varies significantly based on the specific variety planted and the seasonal growing conditions experienced. Understanding the signals your potato plants send is necessary to ensure you collect tubers perfect for either immediate consumption or long-term storage. This guide provides the necessary steps for identifying readiness, using the correct digging technique, and preserving the harvest for months.
Identifying Readiness: The Vine Die-Back Signal
Potato readiness is signaled by the plant’s above-ground foliage, which communicates whether the tubers are still immature or have reached full maturity. There are two distinct harvest windows, each yielding a different type of potato.
The first option is to harvest for “new potatoes,” which are small, thin-skinned, and prized for their tender texture and fresh flavor. These are typically ready approximately two to three weeks after the plants have finished flowering, while the vines are still green and vigorous. Since new potatoes have immature skins that rub off easily, they do not store well and should be used within a few days of being dug.
The second harvest window is for mature, storage-ready potatoes, requiring the plant to complete its full life cycle. The primary signal is the natural die-back, or senescence, of the foliage, as the leaves and stems turn yellow, brown, and eventually wither completely. This indicates the plant has finished directing energy to the leaves and channeled starches into the underground tubers.
It is important to wait an additional two to three weeks after the vines have fully died back before harvesting. This waiting period allows the potato skins to thicken and “set,” a process that dramatically improves their resistance to bruising and their capacity for long-term storage.
For Michigan growers, the mature potato harvest generally occurs from late August through September. Timing the harvest before the first hard frost is critical, as this temperature drop can freeze the soil. While a light frost only damages foliage, a hard freeze can penetrate the soil and damage the tubers, making them unsuitable for storage. If a hard frost is predicted before the waiting period is complete, harvest immediately to salvage the crop.
The Digging Process and Technique
Once the vines have signaled readiness, using the proper technique is necessary to avoid damaging the tubers, which compromises their storage life. Harvesting should be done when the soil is relatively dry, as wet, heavy soil makes it harder to locate the potatoes and increases the chance of skinning or bruising them.
It is recommended to use a specialized potato fork or a standard garden pitchfork rather than a shovel. The flat blade of a shovel is more likely to slice through or severely injure the tubers, whereas a fork’s tines tend to push past them.
Begin digging several inches away from the center of the plant, beyond where the main stem enters the ground, and angle the tool toward the center. This approach helps avoid piercing the cluster of potatoes around the original seed piece. Gently lift the plant and surrounding soil to expose the tubers, then sift through the loosened earth by hand to retrieve all potatoes.
After digging, handle potatoes carefully to prevent skinning and bruising, which creates entry points for pathogens and moisture loss. Immediately brush off any large clumps of soil, but do not wash the potatoes, as moisture encourages rot during storage. Damaged or cut potatoes should be set aside and used within a few days, as they will not last in long-term storage.
Post-Harvest Curing and Storage
The final step before placing the potatoes into long-term storage is the curing process, which is a brief, controlled period designed to heal minor wounds and further toughen the skin. Curing typically takes about ten to fourteen days and takes place in a specific environment.
The ideal conditions include a dark, humid atmosphere with a relative humidity of 85 to 95 percent and temperatures ranging from 50 to 60°F. This warm, moist environment promotes the formation of a protective layer, or cork, over any small abrasions or shallow cuts that occurred during harvest.
Following curing, the potatoes are ready for their final storage location, which must be cool, dark, and humid. The optimal long-term temperature for table stock potatoes is generally between 35 and 45°F, with 40°F being the ideal target. Temperatures below 38°F can cause starches to convert to sugar, resulting in an undesirably sweet flavor and darker fried products.
The storage area must remain completely dark, as exposure to light triggers the production of solanine, a bitter compound that causes the potato skin to turn green. Potatoes should also be stored away from any fruits, such as apples, which release ethylene gas. Ethylene gas acts as a plant hormone that can prematurely break the potato’s natural dormancy, causing it to sprout much sooner than expected.