Dig sweet potatoes 90 to 120 days after planting the slips (Clemson), once they’re big enough to eat, and before the first frost or before the soil cools below 55 °F (Penn State). Then cure them at 80 to 85 °F with high humidity for about a week, and store them at 55 to 60 °F. Never refrigerate them.
When to dig: count the days, watch the frost
Clemson puts the harvest 90 to 120 days after planting; the University of Maryland, 85 to 120 days, and it starts checking root size at 80 to 85 days because the roots don’t stop growing and can split if they get too big. Counted from the day you set out the slips:
| Slips planted | Start checking (85 days) | Harvest window (90–120 days) |
|---|---|---|
| May 1 | July 25 | July 30 to August 29 |
| May 15 | August 8 | August 13 to September 12 |
| June 1 | August 25 | August 30 to September 29 |
| June 15 | September 8 | September 13 to October 13 |
| July 1 | September 24 | September 29 to October 29 |
Our arithmetic from the extension services’ day counts. Varieties differ; the seed packet or plant tag gives the days for yours.
Whatever the calendar says, the cold sets the deadline:
- Before frost. Cool soil lowers the quality and storage life of the roots (Clemson). Penn State lifts them before frost or before the soil drops below about 55 °F.
- Never into cold soil. Soil below 50 °F can cause chilling injury (University of Maryland).
- If frost hits the vines, dig now. Iowa State harvests just before or just after a vine-killing frost, but Maryland warns that decay in frost-killed vines moves into the roots, so don’t leave them in the ground afterward.
Penn State’s Lancaster County gardeners add: if a light frost burns the leaves, don’t wait; and if the harvest has to wait, cut the vines so decay doesn’t spread to the roots. Our frost dates by ZIP code are coming soon.
How to tell they’re ready
There is no sign above ground you can fully trust, so dig a test hill. Clemson harvests when 30 percent of the roots are wider than 3½ inches. The University of Maryland harvests as soon as the roots reach eating size. Penn State’s Lancaster County gardeners harvest when the leaves begin to turn yellow, before a light frost.
How to dig them without damage
- Cut the vines off first. Clemson and Maryland both remove the vines before digging, which makes it easier (University of Maryland).
- Loosen the soil with a garden fork or spade, then lift the roots gently (University of Maryland). The skins scrape easily and the roots bruise (Clemson), and damaged roots store poorly (Iowa State).
- Brush off soil clumps; don’t wash or rub the roots before storing them (University of Maryland).
Cure them, then store them cool
Freshly dug sweet potatoes aren’t ready to eat or store. Curing heals small cuts and bruises and turns starch into sugar, which makes them sweeter (Iowa State, Penn State).
- Cure: 80 to 85 °F and 85 to 95% humidity for 4 to 7 days, or up to 10 days for heavily skinned roots (Penn State); 85 °F and 90% humidity for one week (Clemson). No curing happens below 70 °F (Clemson).
- At home: Clemson puts them in the warmest room of the house, usually the kitchen, for 14 days. Maryland notes it works best if you harvest in September, while it’s still warm and humid.
- Store: 55 to 60 °F and 85 to 90% humidity (Iowa State, Penn State, University of Maryland). Warmer than 60 °F, they sprout; cooler than 55 °F, they develop off-flavors and discolored flesh (Iowa State).
- Never refrigerate them (Clemson, Penn State). Below 50 °F they get off-flavors and may rot (Clemson).
Stored well, they keep for months: 3 to 6 at Penn State, 4 to 6 at Iowa State, over six at Clemson. Their sugar content slowly rises in storage (University of Maryland).
Questions people ask
How long after planting do you harvest sweet potatoes?
90 to 120 days after setting out the slips (Clemson), or 85 to 120 days (University of Maryland). Check the size of a few roots from about 80 days.
Can you leave sweet potatoes in the ground too long?
Yes. They keep growing and can split when overgrown (University of Maryland), and once the soil turns cold or frost kills the vines, the roots lose quality and can rot.
What happens if you harvest sweet potatoes too early?
The roots are small. Dig one plant first: if fewer than about a third of its roots are 3½ inches across, Clemson’s mark, wait and check again, as long as frost isn’t coming.
Can you eat sweet potatoes right after digging?
You can, but they won’t be sweet yet. Curing for a week or more turns starch into sugar (Iowa State, Penn State), and the sugar keeps rising in storage (University of Maryland).
Should you refrigerate sweet potatoes?
No. Clemson and Penn State both say never to refrigerate them: below 50 °F they get off-flavors and may rot.
Sources
- Clemson Cooperative Extension, Home & Garden Information Center, Sweet Potato (Susan James and Robert F. Polomski; revised by Joey Williamson, 2022): 90–120 days; before frost; 30% of roots over 3½ in; cut vines first; cure at 85 °F and 90% humidity for a week, or 14 days in the warmest room; no curing below 70 °F; never below 50 °F or refrigerated; over six months in storage.
- University of Maryland Extension, Growing Sweet Potatoes in a Home Garden (updated 2026): 85–120 days; check at 80–85 days; harvest at eating size before frost, and immediately if vines are frosted; chilling injury in soil below 50 °F; digging; don’t wash; September harvests cure best at home; store at 55–60 °F and 85–90% humidity; sugar rises in storage.
- Iowa State University Extension, How do I harvest and store sweet potatoes?: just before or after a vine-killing frost; cure a week at 80–85 °F and 90–95% humidity; store at 55–60 °F and 85–90%; sprouting above 60 °F, off-flavors below 55 °F; 4–6 months.
- Penn State Extension, Sweetpotato Curing and Storage (Luis Duque, 2025): lift before frost or soil below about 55 °F; cure at 80–85 °F and 85–95% humidity for 4–7 days; store at 55–60 °F and 85–90%; chilling injury below 50–55 °F; don’t refrigerate; 3–6 months.
- Penn State Extension, Sweet Potatoes, a Winning Vine for Your Garden (Michèle Pique, Lancaster County, 2026): harvest before the first killing frost, when the leaves begin to yellow; dig at once if frost burns the leaves; cut the vines if the harvest must wait.