The sweet potato (Ipomoea batatas) is often mistaken for a regular potato, but they are botanically distinct. The common potato is a stem tuber, while the sweet potato is a storage root designed for nutrient storage. Proper harvest timing determines the root’s final flavor, texture, and ability to be stored long-term. Harvesting too early results in underdeveloped roots, while harvesting too late can lead to rapid decay. Recognizing when the long growing cycle has concluded signals the start of the harvest window.
Determining the Optimal Harvest Time
Maturity is reached between 90 and 120 days after the slips are planted, though some varieties may require up to 170 days. Checking the specific days-to-maturity provides the initial calendar guide for the harvest window. Relying solely on the calendar is insufficient, as environmental factors affect the growth rate.
Visual cues from the plant offer a reliable sign that the roots are ready for digging. The vines and leaves naturally begin to yellow and die back as the plant shifts energy to the storage roots. The roots are rapidly bulking up and converting starches, which develops their characteristic sweetness. A cautious test dig on the edge of the row can confirm the roots have reached a desirable size, generally three to four inches in diameter.
The most pressing deadline for harvest is the arrival of the first light frost. Sweet potatoes are sensitive to cold, and the soil temperature should not drop below 55°F. A light frost kills the vines, signaling the need to harvest immediately. A hard frost that penetrates the soil will quickly damage the roots, causing them to rot. Harvesting must occur before the soil becomes chilled, as cold damage reduces storage life and eating quality.
Techniques for Digging Sweet Potatoes
Before digging, the dense mat of vines should be cut back and removed from the patch. This clears the area and prevents the delicate skin of the roots from being scraped during extraction. Some growers cut the vines a few days before harvest, believing this slightly toughens the root skins for minor protection.
Digging requires caution due to the spread of the roots and their easily damaged skin. Sweet potatoes spread widely and do not cluster directly beneath the plant stem like potatoes. Therefore, the digging tool must start well away from the center of the plant. Use a spading fork or dull shovel, beginning to loosen the soil about 18 to 24 inches away from the main stem.
The goal is to gently lift the entire root cluster without puncturing or bruising the roots. Freshly harvested sweet potatoes have tender skin, making them susceptible to damage that leads to rot in storage. Handle the roots with care, brushing off only excess soil. Never wash the roots, as water introduces moisture and pathogens that reduce shelf life.
Curing Sweet Potatoes for Flavor and Storage
Sweet potatoes require curing to reach optimal flavor and storage potential. Freshly dug roots are starchy, less sweet, and have fragile skin, making long-term storage difficult. Curing initiates a biochemical process where starches convert into sugars, enhancing the root’s flavor profile.
The curing process also heals minor nicks and bruises sustained during harvest, which is called suberization. This healing creates a protective, cork-like layer on the skin. This layer prevents moisture loss and resists decay-causing organisms. Without proper curing, the roots will not store well and will likely spoil within a few weeks.
Ideal curing involves exposing the roots to high temperature and high humidity for a defined period. The roots should be kept at 80°F to 85°F with a relative humidity of 85% to 90% for four to fourteen days. While achieving these exact conditions can be challenging for home growers, a warm, enclosed space with moisture can approximate the requirements.
Once curing is complete, the roots should be moved to a cooler location for long-term storage. The best storage temperature is consistently between 55°F and 60°F. Temperatures below this range can cause internal chilling injury, leading to a hard center and reduced quality. When properly cured and stored in a cool, dry, and well-ventilated area, sweet potatoes can be kept for several months.