When to Plant Cucumbers in Seattle, WA
Published: April 21, 2026
Cucumber Planting Dates for Seattle, WA
| Start seeds indoors | April 16–23 |
| Last frost (average) | May 7 |
| Transplant outdoors | May 14–24 |
| Direct sow outdoors | May 14–24 |
| Minimum soil temperature | 60°F |
| Expect first harvest | July 3 – July 23 |
| Fall crop planting | July 23–August 2 |
| Fall crop harvest | September 11 |
| First fall frost (average) | October 1 |
Best Cucumber Varieties for Seattle, WA
For Zone 4b Seattle, the best-performing cucumber varieties are Spacemaster, Bush Pickle, and Fanfare — all short-season varieties chosen for cool-climate reliability. Calypso is worth trialing in containers or a small plot — its extra cold tolerance gives a backup if your main crop is lost to a late spring frost. These varieties are typically stocked by local nurseries and are the safest bets for gardeners new to cucumber in Seattle.
Growing Cucumbers in Seattle
Seattle sits in Zone 4b, with an average last frost of May 7 and first fall frost around October 1 — giving a 147-day frost-free growing season. Warm-season crops like cucumber need soil at 60°F or above before transplanting; Seattle's frost calendar puts that window clearly in the late-spring to early-fall range.
Seattle's short growing season makes indoor seed starting essential for cucumber. Missing the April 16–23 start date by even two weeks often means plants do not reach producing size before the first fall frost shuts them down. Row covers and cold frames extend both ends of the season by 2–3 weeks each.
Seattle's well-draining loam soils are among the best for cucumber growing — focus on annual organic matter additions (2 to 3 inches of compost) and consistent moisture during drier months. Water cucumber at 1.5 inches per week; loam holds moisture evenly without the drought-crack cycle of heavy clay or the rapid-drain losses of pure sand.
Cucumber Calendar for Seattle
| Month | Task |
|---|---|
| April | Start seeds indoors under grow lights |
| May | Transplant outdoors into warm soil |
| July | Expect first harvest window to open |
| July | Start fall crop — transplants or direct sow |
| October | First fall frost — harvest remaining, end of outdoor season |
Cucumber Tips for Seattle Gardeners
- •Direct sow after last frost rather than transplanting — cucumbers establish faster from seed in warm soil.
- •Trellis vertically to save space and reduce powdery mildew from soil splash.
- •Cover transplants with floating row covers for the first 2–3 weeks after setting them out in Seattle. The 3–5°F of extra warmth dramatically improves early establishment.
Common Cucumber Pests in Seattle
- •Cucumber Beetle — peaks July in Zone 4b (active June–August); yellow and black striped beetles that spread bacterial wilt; trap with yellow sticky traps.
- •Squash Vine Borer — peaks July in Zone 4b (active June–August); sudden wilting with frass at stem base; inject Bt into the stem or use row covers through flowering.
- •Powdery Mildew — peaks July in Zone 4b (active June–August); white powdery coating on leaves; improve airflow and apply milk spray (1:9 milk-to-water).
Check plants every 2–3 days during peak season — early intervention prevents most infestations from becoming serious.
What to Plant with Cucumbers in Seattle
In Seattle's cold climate, Radish and Nasturtium are the most beneficial plants to grow alongside cucumber. Radish deters cucumber beetles and matures fast enough to harvest between slower neighbors. Keep cucumber away from Aromatic Herbs — it generally slow cucumber growth when planted too close. In short-season gardens, interplanting companions at transplant time maximizes each bed's productive weeks.
Frequently Asked Questions
When should I plant cucumber in Seattle, WA?
In Seattle (Zone 4b), start cucumber seeds indoors around April 16–23 and transplant outdoors around May 14–24. The city's average last frost of May 7 is the anchor date — count 3 weeks back for seed starting and 1 weeks forward for transplanting.
What zone is Seattle, WA for cucumber growing?
Seattle is USDA Zone 4b. For cucumber, this means a frost-free growing season of roughly 21 weeks running from May 7 to October 1. This is a tight window for warm-season crops like cucumber — short-season varieties maximize harvest.
When is cucumber harvest season in Seattle?
Expect the first cucumber harvest in Seattle around July 3, with harvest continuing through July 23. This is based on 50–70 days from transplant or direct sow. A fall crop planted July 23–August 2 adds a second harvest around September 11.
How long does it take to grow cucumber in Seattle, WA?
From transplant or direct sow to first harvest, cucumber takes 50–70 days in Seattle's climate. Based on a typical planting date of May 14–24, expect your first harvest around July 3. Seattle's cooler Zone 4b climate often lands at the slower end of this range — cooler nights slow fruit development.
What soil does cucumber need in Seattle?
Seattle's loam soil is near-ideal for cucumber. Work in 2–3 inches of compost before planting to boost organic matter and nutrient content. Minimal amendment is needed beyond that — loam holds moisture evenly without the drought-crack cycle of clay or the nutrient-loss issues of sandy soil.