When to Plant Sweet Potatoes in New Hampshire
Published: April 24, 2026
New Hampshire gardeners in Zone 5b have a 28-week frost-free window for sweet potato (April 7 to October 22). Warm-season crops like sweet potato must be started indoors early to maximize the short window — New Hampshire's late spring and early fall frost dates leave little room for error. This guide gives exact dates for New Hampshire based on your local frost calendar.
Sweet Potato Planting Dates for New Hampshire
| Start seeds indoors | Year-round |
| Last frost (average) | April 7 |
| Direct sow outdoors | April 28–May 8 |
| Expect first harvest | July 27 – August 26 |
| First fall frost (average) | October 22 |
Dates above assume Zone 5b, the most common zone in New Hampshire. Gardeners in cooler Nashua (Zone 5b) plant 1–2 weeks later; warmer Portsmouth (Zone 5a) can plant 1–2 weeks earlier.
⚠ Plant sweet potato slips 2–3 weeks after last frost when soil is consistently above 60°F. Needs 90–120 days of warm weather. Best in Zones 5–11.
Growing Sweet Potatoes in New Hampshire's Climate
New Hampshire's cold Zone 5b climate puts warm-season sweet potato at the edge of viability — but the edge is workable with good planning. Starting seeds indoors under lights in late winter is the most important step; skipping this puts the whole harvest at risk from the short outdoor growing window.
Season extenders pay for themselves many times over in New Hampshire. Row covers placed over transplants in early spring add 5°F to 8°F of protection and can extend the season two to three weeks on each end. Black plastic mulch warms the soil to the temperatures sweet potato needs for aggressive root growth.
Common sweet potato pests to watch for in New Hampshire include Sweet Potato Weevil and Wireworm. The first line of defense is companion planting: Bush Bean and Pea planted nearby discourage several of these pests by confusing host-plant identification or repelling adults before they can lay eggs. Weekly garden walks in the early morning catch problems when they're still manageable.
Sweet Potato Garden Calendar for New Hampshire
| Month | Task | Notes |
|---|---|---|
| January | — | Dormant season |
| February | — | Dormant season |
| March | — | Dormant season |
| April | Direct sow seeds | Sow seeds 1/4–1/2 inch deep, 12 inches apart |
| May ← | — | Dormant season |
| June | Peak growth; water 1 inch/week | Monitor for pests daily; stake or support as needed |
| July | Continue care | Consistent watering; remove yellow leaves |
| August | — | Dormant season |
| September | — | Dormant season |
| October | First frost approaches | Harvest remaining sweet potato; cover plants on frost nights |
| November | — | Dormant season |
| December | — | Dormant season |
Sweet Potato Growing Tips for New Hampshire Gardeners
- •Order slips in early spring from a seed company; plant within 24 hours of arrival in pre-warmed soil.
- •Form raised ridges or mounds 10 inches tall — sweet potatoes size up best in loose, warm, well-drained soil.
- •New Hampshire's short growing season means start seeds indoors under grow lights — don't rely on windowsill light which produces leggy, weak seedlings that struggle outdoors.
- •Cover young transplants with floating row covers for the first 2–3 weeks outside. The 3–5°F of protection reduces frost damage risk and accelerates early growth.
- •Black plastic mulch warms soil quickly in northern climates and can add 2 weeks to the effective growing season.
Companion Planting for Sweet Potatoes in New Hampshire
In New Hampshire's cold climate, planting sweet potato with Bush Bean and Pea helps deter pests and improve soil. Avoid planting near Squash and Tomato, which inhibit sweet potato growth through root chemistry or shared pest pressure. See the full sweet potato companion planting guide for the complete list.
Sweet Potatoes Planting Dates by City in New Hampshire
Top cities in New Hampshire — select for city-level frost dates and planting calendars.
Frequently Asked Questions
When should I plant sweet potato in New Hampshire?
In New Hampshire (Zone 5b), start sweet potato seeds indoors around Year-round and transplant outdoors around null — 3 weeks after the state's average last frost of April 7.
What is the last frost date in New Hampshire?
New Hampshire's average last frost date is April 7 in the state's most common Zone 5b. Frost dates vary by city — higher elevations and northern counties run 1 to 3 weeks later than the state average. See the city list below for city-level frost dates.
Can I grow sweet potato year-round in New Hampshire?
Not year-round — New Hampshire's cold season stops sweet potato production. The sweet potato season runs April 7 to October 22, roughly 28 weeks.
What sweet potato varieties grow best in New Hampshire?
For New Hampshire's Zone 5b, consult a local nursery or extension office for sweet-potatoes variety recommendations.
When do I start sweet potato seeds indoors in New Hampshire?
Sweet potato does not need indoor starting in New Hampshire — direct sow around April 28–May 8 once soil reaches 60°F. Indoor starting is not recommended for this crop because sweet potato transplants poorly.