When to Plant Sweet Potatoes
Planting Window
- Transplant slips
- Soil above 65°F, nights above 60°F, several weeks after last frost
| USDA Zone | Typical Window |
|---|---|
| Zone 5 and colder | Mid-June at the earliest, tight maturity window |
| Zone 6-7 | Late May to early June |
| Zone 8 and warmer | May-June, plenty of season to mature |
Sweet potatoes aren't a nightshade and aren't planted like white potatoes despite the similar name and root habit - they're started from slips, rooted shoots grown from a mature sweet potato, and they need genuinely warm soil, more so than almost any other crop covered here.
Slips, Not Seed Potatoes
A slip is a small rooted sprout grown from a stored sweet potato, either home-grown by suspending a potato in water or burying it partway in damp soil several weeks before planting time, or bought pre-grown from a garden supplier. Planting a whole sweet potato directly the way you'd plant a seed potato doesn't work the same way and isn't the standard method.
Transplant Only Once Soil Is Genuinely Warm
Slips need soil temperature reliably above 65°F and nighttime air staying above 60°F before they take off - notably later in the season than tomatoes or peppers want in the same zone, since sweet potato's tropical origins make it even less tolerant of cool soil than most of the nightshades it's sometimes mistakenly grouped with.
Why Freshly Dug Sweet Potatoes Aren't Very Sweet
A sweet potato pulled straight from the ground at harvest is noticeably starchier and less sweet than one that's been cured - held for one to two weeks in warm, humid conditions after digging, which converts some of that starch into sugar. This is really a harvest-and-storage step rather than a planting one, but it's part of why the long 90-120 day maturity window matters: a late-planted crop that barely matures before frost leaves little slack for a proper curing period afterward.
Black Plastic Mulch Genuinely Helps in Cooler Zones
Because soil warmth is the binding constraint, black plastic mulch laid down ahead of planting to pre-warm the bed is a more commonly recommended technique for sweet potatoes than for most other crops on this site - it's less about weed suppression here and more specifically about closing the gap between a marginal zone's actual soil temperature and what the crop wants.
Zone boundaries follow the USDA Plant Hardiness Zone Map (2023 revision); frost windows reflect NOAA/NCEI climate normals. Both are typical historical ranges, reviewed annually - not a forecast or a guarantee for any single year. See Methodology & Sources.
Frequently Asked Questions
Can I use a sweet potato from the grocery store to grow my own slips?
Sometimes, though many grocery store sweet potatoes are treated to prevent sprouting, which defeats the purpose - a certified organic sweet potato, or one specifically sold as a seed variety by a garden supplier, is a more reliable starting point than an untreated grocery store one.
How long does it take to grow slips before they're ready to plant?
Roughly six to eight weeks from starting a sweet potato sprouting in water or soil to having slips large enough to separate and plant - factoring that lead time in when planning backward from your ideal transplant date matters more for sweet potatoes than for crops started from packet seed.
My slips are ready to separate, but the soil is still too cool to transplant - can I hold onto them for a while?
Briefly, yes - keeping separated slips standing in a jar of water on a windowsill, similar to how you'd hold scallion cuttings, buys some time without losing them, and many will even grow small roots while waiting. Don't stretch this out for weeks, though; slips held too long get leggy and weaker before transplanting than ones moved into the garden promptly once soil temperature actually catches up.