When to plant sweet potatoes in Portland, Maine
May 10 – May 24
Transplant outdoors · typical Portland yearClimate basis: NOAA station Portland INTL Jetport, ME (USW00014764), 2 mi (4 km) from downtown Portland (ZCTA 04101 centroid), elevation 45 ft, on the 1991–2020 climate normals. Plant sweet potato slips from approximately the dates above, anchored to the median last spring 32°F freeze (April 26). One year in ten still freezes after May 7.
The Portland year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to May 7
Every method, with its sources
Transplant outdoors
May 10 – May 24Purdue: very tender (vegetatively propagated) — plant slips at least two weeks after the average last frost. Anchored to the median last spring freeze (Apr 26). Purdue University Extension
Start seeds indoors
Not calculatedThe cited extension guides do not time an indoor seed-starting window for this crop.
Direct-sow outdoors
Not calculatedSweet potatoes are grown from slips, not seed.
Fall planting
Not calculatedNo source-backed fall planting rule exists for this crop in the registry, so no fall window is calculated.
Variety assumption: Assumes an average variety (about 100–120 days of warm weather from slips).
These windows describe typical years (1991–2020 climate normals), not this year's forecast. Freezes happen outside them — especially in frost pockets, valleys, and urban edges. Watch the forecast before committing tender plants.
Crop rule sources (1)
- Purdue University Extension: Indiana Vegetable Planting Calendar (HO-186-W) (accessed 2026-07-24)Hardiness classes: hardy = plant 4-6 wk before last spring frost; semi-hardy = 2-4 wk before; tender = after average last frost; very tender = at least 2 wk after. Table 2: fall planting at least 4-8 wk before first fall frost.