Oregon planting calendar

When to plant sweet potatoes in Oregon — sow, transplant & harvest dates

Oregon is mostly USDA zone 8b (range 4b-9b). Dates below are derived from sweet potatoes's frost tolerance and Oregon's frost window — not generic national averages.

Sweet potatoes planting timetable for Oregon

Stage	When in Oregon	Anchor
Start seeds indoors	early March (March 4)	6 weeks before the last frost (mid-April (Willamette Valley))
Transplant outside	early May (May 6)	21 days after the last frost (mid-April (Willamette Valley))
First harvest (estimate)	mid-August (August 19)	~105 days from transplant

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why Oregon's climate shifts the sweet potatoes dates

Oregon's last spring frost averages mid-April (Willamette Valley) and first fall frost early November (Willamette Valley), which sets the whole planting clock. Oregon is split by the Cascades: a mild, wet, long-season west and a cold, dry, short-season high desert east. Wait for warm soil — sweet potatoes stall in cold ground even after the air warms, so don't rush them out.

Sweet potatoes are extremely frost-tender and demand warm soil — do not transplant slips until soil temperature at 4-inch depth holds at 18 °C (65 °F) or above, typically 3 weeks after the last spring frost. Short-season zones (z5-6) should start slips indoors under lights 5-6 weeks early to ensure 100-120 frost-free days. Avoid zones 3-4 without a floating row cover season-extension strategy; in z9-11 slips can go out as early as late March.

Frost-risk note

Don't plant before mid-April (Willamette Valley) — even a light frost will kill seedlings overnight. In the high desert and Cascades east of the mountains (zone 4b) the safe date runs a week or two later.

Regional variation within Oregon

the high desert and Cascades east of the mountains (zone 4b) runs roughly 1-2 weeks behind the state average; the Willamette Valley and southwest interior (zone 9b) can plant 1-2 weeks earlier.

Portland — USDA zone 9a
Eugene — USDA zone 8b
Salem — USDA zone 8b
Bend — USDA zone 6b
Medford — USDA zone 8a

What else to plant in Oregon around then

Pair the post-frost slot with other warm-season crops — peppers, beans, squash, and cucumbers.

Quick-grow guide

Sun: Full sun — 6-8 hours direct.
Soil temperature for germination: Soil 18-24 °C (65-75 °F) for slip rooting.
Spacing: 12-18 inches (30-45 cm) between plants.
Days to harvest: ~105 days from planting out.

Frequently asked questions

When is the best time to plant sweet potatoes in Oregon?

In Oregon (mostly USDA zone 8b), sow sweet potatoes indoors around early March, transplant outdoors early May (after the last frost, mid-April), and harvest from mid-August. Sweet potatoes are frost-tender — a single light frost kills seedlings, so they only go outside once frost danger has fully passed and the soil is warm.

What USDA zone is Oregon?

Most of Oregon sits in USDA hardiness zone 8b, with the state spanning roughly 4b-9b from the high desert and Cascades east of the mountains (zone 4b) to the Willamette Valley and southwest interior (zone 9b). The last spring frost averages mid-April (Willamette Valley) and the first fall frost early November (Willamette Valley).

Can you grow sweet potatoes in Oregon?

Yes. Oregon's dominant zone 8b supports sweet potatoes — the key is timing. Sweet potatoes are frost-tender — a single light frost kills seedlings, so they only go outside once frost danger has fully passed and the soil is warm.

Does the planting date change across Oregon?

the high desert and Cascades east of the mountains (zone 4b) runs roughly 1-2 weeks behind the state average; the Willamette Valley and southwest interior (zone 9b) can plant 1-2 weeks earlier.

What else can I plant in Oregon around the same time?

Pair the post-frost slot with other warm-season crops — peppers, beans, squash, and cucumbers.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.