Garden
When to Plant
Sweet Potato Slips: The Sprouts Are the Plant
Those sprouts are the plant. A sprouted sweet potato grows slips — shoots you snap or cut off and plant, with or without roots on them. Raising them takes about six weeks, and they only go out once the soil hits 65°F, so a potato sprouting in late summer is next year's crop.
What a slip actually is
If you have a sweet potato in the cupboard that has started putting out shoots, nothing has gone wrong. That is the plant.
Mississippi State University Extension: "Sweetpotatoes are produced from vegetative stem tip cuttings, or “slips.” Slips are produced from sprouted sweetpotato storage roots saved from the previous year’s crop."
So the sweet potato is not a seed. It is a nursery. Unlike almost everything else in the garden, you do not plant the thing you are holding — you grow shoots off it and plant those. Utah State says the same in fewer words: sweet potatoes are "grown from slips, which are plant sprouts from the root. They can also be grown from vine cuttings."
And the question everybody asks first, answered in one line. Mississippi State: "Slips may or may not have roots when they are cut." Roots hanging off it or no roots at all, it is still a slip and it will still grow.
Why your supermarket one never sprouted
This is the most useful sentence on the page and it is missing from nearly every article about putting a sweet potato in a jar.
University of Maryland Extension, on where to get roots to start from: "Buy certified seed stock at a garden center or your favorite varieties from a market. Wash any purchased roots to remove anti-sprouting chemicals."
Supermarket sweet potatoes are treated so they will not do this. That is the whole point of the treatment — a root that sprouts on the shelf is a root nobody buys. So if you have tried this before and watched a sweet potato sit in a jar for a month doing nothing, that was probably not you and not the method.
The fix is one step: wash it properly before you start. And if the one in your cupboard has sprouted anyway, it has told you what you need to know about how it was handled.
Certified stock is a real distinction, not a snobbery. Maryland names it first for a reason — bought-for-planting roots come with a known variety and a known health status, and a market root comes with neither. For a few plants in a home garden that is a fair trade. It is worth knowing you are making it.
Two ways to raise them
Utah State gives both, and which one you want depends entirely on how many plants you are after.
- For a few plants: suspend the root in water. Utah State's method for a small number is to grow your own slips from a root suspended in a container of water. Half in, half out. Utah State does not say how to hold it there and we are not going to pretend otherwise — cocktail sticks pushed into the sides and resting on the rim is the usual improvisation.
- For more: bed the roots in sand. Utah State again: place several sweet potato roots about one inch apart in a hotbed and cover with two inches of sand. Keep the bed moist but never waterlogged.
- Keep it warm — this is the part that decides everything. Utah State puts the target at a soil temperature of 70 to 80°F through the sprouting period. A cool room will stall them rather than kill them, which is harder to notice than a failure — nothing appears to be going wrong.
- Wait about six weeks. Utah State: the slips are ready to pull in about six weeks, once they are rooted and six to eight inches tall. Maryland gives the same figure from the other end — the process from bedding to planting takes six weeks.
Six weeks is not a detail, it is the whole calendar. Whatever date you are hoping to plant out, the sweet potato has to go into water or sand six weeks before it.
What a good slip looks like, and how to take it
Not every shoot is worth planting, and Mississippi State gives a bar you can actually hold one up against.
"A good sweetpotato slip should be firm, green, and 8 to 12 inches long, preferably with one or two leaves." Firm and green rather than pale and floppy; long enough to have something to plant.
Cut them rather than pulling them. Mississippi State's own caption describes slips being "cut 1 inch above the soil surface from slip production beds". Why an inch rather than at the surface is not stated on the page, so we will not invent a reason. What is clear is that a slip is cut rather than pulled.
Utah State's timing, again, is the check: rooted and six to eight inches tall at about six weeks. Mississippi State's bar of eight to twelve inches is the same plant a little further on.
When they go out, and whether this year is still possible
Here is the arithmetic, done out loud, because this is where most advice quietly stops.
Slips go out on warm soil, not on a date. Maryland: "Plant sprouted new shoots (called "slips") after the soil has warmed to 65°F." Utah State adds the other condition — "Slips are planted in the field after the danger of frost is over."
Then the crop needs its season. Mississippi State puts most varieties at "between 90 and 120 days" to maturity, and says they "should be harvested in the late summer to early fall before soil temperatures drop below 60°F." Our own record says the same: 90 to 120 days from transplant.
So add it up. Six weeks to raise the slips, then soil at 65°F, then three to four months of growing, finished before the soil drops back below 60°F. For most of the United States that means a sweet potato sprouting on your counter in August is next year's crop, not this year's — and starting it now, in a warm room, is a perfectly good way to have slips ready in spring.
That is an unsatisfying answer and it is the true one. And the failure mode is worth naming, though it is our reading rather than a line in any of these sources: a sweet potato planted too late does not give you smaller roots, it gives you vines. If you want to know what the other kind of potato is doing meanwhile, that one has its own two-week rule.
Sweet potato slip questions people actually ask
Can you plant a sweet potato from the grocery store?
You can grow slips from one, and Maryland says to wash it first to remove anti-sprouting chemicals. Certified seed stock from a garden center comes with a known variety and known health status; a market root comes with neither. For a few plants in a home garden that is a fair trade to make knowingly.
Do sweet potato slips need roots before planting?
No. Mississippi State is explicit that slips may or may not have roots when they are cut. What matters more is the slip itself — firm, green, eight to twelve inches long, ideally with a leaf or two on it.
How long does it take to grow sweet potato slips?
About six weeks. Utah State says slips are ready to pull once they are rooted and six to eight inches tall, at roughly six weeks, and Maryland gives the same figure for the whole process from bedding to planting. Count backwards from when your soil will hit 65°F.
Is it too late to plant sweet potatoes this year?
Do the subtraction. Six weeks to raise slips, then soil at 65°F, then 90 to 120 days of growing, finished before the soil falls below 60°F. In most of the country a sweet potato sprouting in August is next spring's crop. Planting too late gives vines, not roots.
Sources
Every planting date, depth, and temperature on this page traces to these university extension guides. Where they differ, the ranges above hold the whole spread.
- Mississippi State University Extension — Growing Sweetpotatoes in the Home Garden
- University of Maryland Extension — Growing Sweet Potatoes in a Home Garden
- Utah State University Extension — Sweet Potatoes in the Garden
We are building GardenTrack to do that subtraction for you against your own frost dates, so "is it too late" is a yes or a no rather than a guess — the app is in beta now, invite-only.