Mold, soft or mushy spots (especially ones deeper than about a quarter inch into the flesh), a sour or musty smell, and extensive sprouting combined with shriveling are the clear signs a sweet potato has gone bad. A few small sprouts on an otherwise firm sweet potato, by contrast, are a normal, harmless part of storage and don't mean it needs to be thrown out.
Sweet potatoes are a sturdier vegetable than a lot of produce, which is part of why the difference between "still fine" and "actually spoiled" is worth knowing clearly, rather than tossing one at the first sign of a small cosmetic change.
Mold: a clear signal, with one caveat
Visible mold, usually appearing as fuzzy white, black, or green patches, is one of the more unambiguous signs a sweet potato has spoiled. If the mold is limited to a very small surface spot and the rest of the sweet potato is firm, some guidance allows cutting around it generously; but if mold spots are deep, widespread, or paired with any softness, the safer approach is discarding the whole sweet potato, since mold can spread through the flesh well beyond what's visible on the outside.
Soft spots: how deep matters
Soft or mushy areas, particularly near the ends of a sweet potato, signal internal rot rather than just surface aging. Per FDA safe-handling guidance, a soft spot that penetrates more than about a quarter inch into the flesh compromises the whole vegetable, not just the immediately affected area, which means cutting away a shallow soft spot may not fully address the problem if it goes any deeper than that.
Reading the smell
Fresh sweet potatoes have a mild, earthy, slightly sweet smell. Early spoilage tends to shift that toward a faint, vinegar-like note, while more advanced spoilage produces a distinctly sour or unpleasant odor. A moldy sweet potato often smells musty, similar to a damp basement. Any of these smell changes are worth trusting over a sweet potato's outward appearance, since smell often signals spoilage before it's fully visible.
Sprouting: usually fine in small amounts
Small sprouts, generally under about 2 inches, are a normal part of a sweet potato aging in storage and don't necessarily mean it's spoiled. If the flesh underneath remains firm, removing the sprouts and cooking the sweet potato as usual is a reasonable, safe approach.
Extensive sprouting paired with visible shriveling is a different situation, signaling more significant nutrient loss and a genuine decline in quality, at which point discarding it rather than trying to salvage it is the more sensible choice.
Wrinkling and dark spots
Deep wrinkles across the skin, beyond the light surface texture a sweet potato naturally develops over time, along with dark spots not explained by normal bruising, are both worth treating as spoilage signs, particularly when they show up alongside any of the other signals covered above.
How long sweet potatoes actually last
Stored properly, in a cool, dark spot with reasonable airflow, sweet potatoes generally hold for 3 to 5 weeks. Left at room temperature without those specific conditions, they tend to start declining within 2 to 3 weeks instead. A sealed plastic bag is specifically worth avoiding, since it traps moisture against the skin and accelerates spoilage rather than protecting the sweet potato.
Once it's cooked, a different clock applies
Everything above concerns raw sweet potatoes in pantry storage. Once cooked, a sweet potato moves onto the same cooked-food storage timeline as mashed potatoes and other cooked sides, generally a few days refrigerated rather than the weeks a raw one holds up in a cool, dark pantry.
Why sweet potatoes hold up longer than a lot of produce
Sweet potatoes are a root vegetable with a naturally thick skin and a lower moisture content than something like a tomato or a leafy green, which is part of why they can hold for weeks in the right conditions rather than the days a more delicate vegetable typically manages. This durability is also why a small cosmetic imperfection, a bit of surface wrinkling or a couple of small sprouts, doesn't necessarily signal the same level of decline it might on a softer, more perishable vegetable, since sweet potatoes are built to hold up under longer storage by nature.
This doesn't mean sweet potatoes are immune to spoilage, just that the visual and textural signs worth watching for tend to appear later in their storage life than they would on produce that spoils faster to begin with, which is part of why the specific markers covered above, depth of a soft spot, extent of sprouting, presence of mold, matter more than a general sense of how long a sweet potato has been sitting around.
The role of temperature swings in accelerating spoilage
Sweet potatoes stored somewhere that swings noticeably between warm and cool, near a stove, in direct sunlight, or in an uninsulated space that shifts with the weather outside, tend to spoil faster than ones kept in a genuinely stable, cool, dark spot. Consistent conditions matter as much as the general temperature range itself, since repeated warming and cooling can accelerate the same soft-spot and mold development covered above even within a nominally cool storage area.
Choosing a storage spot specifically for its consistency, a pantry shelf away from appliances and windows rather than merely "somewhere cool," is a simple change that can meaningfully extend how long a batch of sweet potatoes stays in good condition before any of the spoilage signs start to appear.
Cut or peeled sweet potato behaves differently than a whole one
Once a sweet potato has been cut or peeled, it no longer follows the weeks-long raw storage window covered above for a whole, unbroken sweet potato, since cutting exposes the interior flesh to air and bacteria in a way the intact skin normally prevents. A cut sweet potato should be refrigerated and used within a few days, closer to how any other cut raw vegetable is handled, rather than treated with the same multi-week timeline that applies to a whole one sitting in a cool, dark pantry.
Submerging cut sweet potato pieces in water in the refrigerator, changing the water daily, can help prevent browning and extend usability slightly within that shorter window, similar to a technique sometimes used for other cut root vegetables and potatoes, though this doesn't return the cut pieces to anything close to a whole sweet potato's original weeks-long shelf life.
Comparing sweet potato spoilage signs to a regular potato
Sweet potatoes and standard white or russet potatoes share several spoilage signs in common, mold, soft spots, and sprouting among them, but sweet potatoes are somewhat more prone to visible surface changes during storage given their higher natural sugar content, which is part of why a sweet potato's skin sometimes develops a slightly different appearance over time than a standard potato's would under similar storage conditions. This doesn't mean sweet potatoes spoil faster overall; both types generally hold up for a comparable number of weeks under similar cool, dark storage, but the specific visual cues worth watching can look a little different between the two, given their differing sugar and moisture profiles.
Applying the same general principles, mold and deep softness mean discard, small sprouts alone don't, and smell often signals a problem before appearance does, works reliably across both types, even though the exact visual details of spoilage differ somewhat between a sweet potato and a standard one.
Putting it together
A sweet potato with a couple of small sprouts, a bit of surface wrinkling, and no soft spots or off smell is still perfectly fine to cook and eat. One with deep soft spots, mold beyond a tiny surface patch, a sour smell, or extensive sprouting and shriveling has crossed into spoiled territory and is better discarded than salvaged.
The short version: trust smell and depth of any soft spots more than surface appearance alone. Small sprouts are normal; mold, deep softness, and a sour or musty smell mean it's time to let it go.