When to plant sweet potato in Seattle

In Seattle, typical last spring frost is March 25 and typical first fall frost is November 20. Typical last spring frost: March 25. Sweet potato in Seattle is not realistic outdoors: 0 suitable days are fewer than the 85 days this plant usually needs.

Sweet potato

How to grow Sweet potato Seattle climate Weekly temperatures and windows

Where are you growing?

Not realistic outdoors

Not realistic in greenhouse

Tight fit in a cold frame

Sweet potato in Seattle is doable with planning under fleece. 103 suitable days are enough for fast varieties (85 days) but not slow ones (140 days).

When to plantMay 12 – June 24

Harvest: August 5 – November 5
Season vs crop: 103 grow days vs 85–140 needed
Typical frost (last spring – first fall): February 25 – November 29

Sweet potato in Seattle is doable with planning under fleece. 103 suitable days are enough for fast varieties (85 days) but not slow ones (140 days).

Start slips March 31 – May 13, then transplant May 12 – June 24 so the crop can finish under fleece.

Estimate. Protection varies with the cover, the weather and how you vent it.

Fleece adds about 1–4 °C on frosty nights, depending on its weight. Remove it on warm days.

Fleece also cuts light: about 5–10 % for light fleece, up to 50–70 % for heavy grades. Take it off by day once frosts are over.

Cover dates are modelled from weather-model data using published greenhouse studies. They are not measured in your greenhouse. A max–min thermometer inside will tell you more.

Typical last frost estimate range March 8 – January 30, depending on the cover and the night.

Planting conditions

Suitable growing days in a row103

Days to harvest85–140 days from planting

No planting window is recorded for this place.

Too cold
Frost line

Blue fill is usually too cold for this plant. Dashed lines are typical last and first frost (35 seasons (1991–2025)). Adjust a week or two for your conditions.

Protected frost and sowing dates are modelled estimates from weather-model data and published greenhouse studies, not measured in your greenhouse. A max–min thermometer inside will tell you more.

Planting and growing across the year

Planting is the sow / plant-out window. Growing is daytime air versus this plant’s ideal (21 – 32 °C70 – 90 °F21 – 32 °C (70 – 90 °F)) and tolerable (16 – 35 °C61 – 95 °F16 – 35 °C (61 – 95 °F)) ranges, from modelled cover temperatures for the growing method you selected.

Ideal / plantable
Tolerable
Too cold
Too hot
Outside window

Planting uses sow / plant-out rules; growing shows daytime air against this plant’s ideal and tolerable ranges.

Key dates

Typical last spring frostFebruary 25

Low-risk last spring frostMarch 9

Typical first fall frostNovember 29

Low-risk first fall frostNovember 5

Frost-free days276

Earliest indoor seed startMarch 31

Latest indoor seed startMay 13

Transplant outdoorsMay 12 – June 24

Direct sow windownot recommended here

Suitable growing windowMay 12 – August 22 (103 days)

Expected harvestAugust 5 – November 5

How these dates are judged

Ideal conditions: Daytime air from 21 – 32 °C70 – 90 °F21 – 32 °C (70 – 90 °F).
Suitable conditions: Daytime air from 16 – 35 °C61 – 95 °F16 – 35 °C (61 – 95 °F).
Last frost and first frost: Typical spring and fall frost dates for Seattle, shown in the key dates.
Days to harvest: 85–140 days from planting, from typical days to harvest.
Sowing window: Dated sow and harvest bars use frost dates, soil minima, night limits, and last-sow count-back from typical crop timing. Air ratings on the weekly chart colour only weeks inside that same window — see weekly temperatures and windows.

Other plants for Seattle

Calculated by Plan & Plant. Method. Data 35 seasons (1991–2025).

Frost and suitability dates are typical figures from climate statistics.

Based on 35 years (1991–2025) of ERA5-Land data from Open-Meteo, for an area of about 10 km. Typical dates, not a guarantee.

Dates for Seattle use ERA5-Land cell 47.60, -122.30. How we calculated this · Algorithm 2026-10-season-10.

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