When to Harvest Sweet Potatoes

How long sweet potatoes take

Clemson and UGA both put harvest at about 90 to 120 days after planting slips. Fast varieties such as ‘Beauregard’ are at the short end, and Clemson gives it 90 to 100 days. ‘Jewel’ takes 120 to 135. UF/IFAS gives a range of 85 to 130 days, Utah State says 4 to 5 months, and University of Arizona’s low-desert calendar allows 120 to 160 days. Mark the expected date when you plant, then start watching the plants.

Signs the roots are ready

• Leaves yellowing. Texas A&M reads yellowing leaves as the signal that vine growth has stopped and the roots have matured. UGA describes the tops dying back as harvest nears.
• Root size. Clemson’s test is to dig one plant and look. When about 30 percent of the roots are over 3½ inches in diameter, it’s time.
• Early sampling. You don’t have to wait for the whole crop. Utah State says you can take a few roots from late summer by reaching into the side of the bed. Roots are usable at 1½ to 2 inches thick, and the plant keeps growing.

Frost and cold soil

The sources agree that cold soil hurts sweet potatoes, but they differ on frost. Clemson and UGA say to harvest before the first frost because cool soil reduces quality and shortens storage life. Texas A&M considers the best time to be just before or just after the first fall frost. Utah State says most gardeners wait until the foliage yellows or frost damages the leaves, but always before the soil freezes. In its New Hampshire trials, UNH dug as late as possible while the soil stayed above 60°F.

Whichever you follow, don’t let the roots sit in cold or freezing ground.

Before you dig

Stop watering ahead of harvest. Texas A&M says 2 to 3 weeks before, and UGA says 3 to 4. Heavy rain or watering in the last few weeks splits roots (Utah State), and a drier finish helps prepare them for storage.

Clemson recommends cutting and removing the vines before you dig.

Digging gently

Sweet potato skin is thin and bruises easily. Texas A&M notes that even dropping roots into a bucket can injure them. Dig with a spading fork or shovel, taking care not to bruise, cut or puncture the roots (Utah State).

Curing

Curing heals wounds so the roots store well, and it converts some starch to sugar (Clemson). The recommendations vary slightly:

• Clemson: 85°F and 90 percent humidity for one week. Without a curing space, keep them in the warmest room in the house, often the kitchen, for 14 days. No curing happens below 70°F.
• Penn State: 85°F and 85 to 90 percent humidity for 7 to 10 days.
• Utah State: 1 to 2 weeks at about 80°F.
• UGA: Air-dry for several days in the shade at 80 to 85°F.

If you can’t match those conditions, Clemson’s warm-room method works for most home gardeners.

Storage

After curing, move the roots somewhere cool but not cold. Clemson’s firm rule is never below 50°F and never in the refrigerator, because chilling causes off-flavors and rot. Utah State recommends 50 to 55°F in a dry place, and UGA says not below 55°F. Storage life also varies by source. Utah State gives 3 to 4 months, UGA up to 6 months, and Clemson more than six months under good conditions. Check stored roots regularly and remove any that show decay before it spreads (UGA).

Wait before eating

Freshly dug sweet potatoes aren’t at their best yet. In UNH’s multi-year trials, sugar content in the roots climbed steadily for about 21 days after harvest before leveling off, and higher sugar went with better flavor scores. The researchers’ advice is to wait at least three weeks after digging, whatever the variety.