When to Plant a Vegetable Garden in Seattle: Last Frost Dates by Crop Type

Planting

Planting a vegetable garden in Seattle at the right time means the difference between a bountiful harvest and a sad pile of frost-nipped seedlings.

Seattle’s unpredictable weather can make or break your 🥬 garden—planting at the wrong time risks frost damage or stunted growth. Timing is everything, and knowing the last frost dates for your specific crops ensures a thriving harvest from spring to fall.

With USDA Zone 8a conditions, your best windows are mid-March to mid-May for cool-season crops and late July to early September for warm-season varieties.

But even those dates shift with microclimates—urban heat islands warm up faster than rural areas, and a single cold snap can turn a perfect planting day into a disaster.

In this guide, I’ll walk you through the exact planting schedule for Seattle’s top vegetables, how to adjust for your specific location, and the pro tips to extend your growing season—so you can enjoy fresh tomatoes in July and kale in November.

🥬 When to Plant Vegetable Garden Garden

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Ideal Time

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Seattle’s last frost dates and ideal planting windows by month

Seattle’s last average frost date typically falls between April 15 and May 15, while the first frost usually arrives between October 15 and November 15. These dates create a 165-day frost-free growing season, perfect for both cool-season and warm-season crops.

However, microclimates—especially in urban areas—can shift these windows by 2-3 weeks, so always check local forecasts.

For cool-season crops like lettuce, spinach, and peas, I start seeds indoors 4-6 weeks before the last frost (around March 1). These hardy plants thrive in 50-65°F soil temperatures and can even handle light frosts.

Warm-season crops like tomatoes, peppers, and cucumbers, however, need to wait until after May 15 when soil temperatures consistently stay above 60°F.

Urban gardeners in Seattle neighborhoods often experience warmer microclimates due to concrete and buildings, which can delay frost by 1-2 weeks. Rural areas, on the other hand, tend to cool faster.

To adjust, I recommend using WSU Extension’s frost date maps or setting up a minimum-maximum thermometer in your garden for real-time data.

Here’s a quick reference for month-by-month planting windows in Seattle, tailored to both cool-season and warm-season crops:

Best vegetables to plant in Seattle’s spring and fall gardens

Seattle’s cool, wet springs and mild falls create perfect conditions for a year-round vegetable garden. The key is selecting cold-hardy crops for spring and heat-tolerant varieties for fall. With USDA Zone 8a conditions, you can enjoy fresh produce from March through October—if you time it right.

For spring planting, focus on leafy greens, root vegetables, and cool-season brassicas that thrive in 50–65°F soil. In fall, opt for fast-maturing warm-season crops like tomatoes and peppers, or hardy greens that can handle cooler temperatures before the first frost.

Let’s break down the top performers for each season.

🌱 Spring Planting Highlights (March–May)

1. Leafy Greens: Lettuce, spinach, kale – sow 4–6 weeks before last frost (mid-March). Space 6–12 inches apart; thrive in partial shade.
2. Root Vegetables: Carrots, radishes, beets – plant soil temps 40–65°F. Loosen soil to 12 inches deep; avoid rocks. Harvest radishes in 30 days, others in 60–90 days.
3. Brassicas: Broccoli, cauliflower, cabbage – start seeds indoors 6–8 weeks before last frost. Transplant 18–24 inches apart; add compost for sulfur-loving plants.
4. Peas & Beans: Sugar snap peas (direct sow March–April) and bush beans (plant after soil warms to 60°F). Use trellises for peas; mulch beans to retain moisture.

🍂 Fall Planting Highlights (July–September)

1. Fast Tomatoes: Cherry tomatoes (e.g., ‘Sweet 100’) – transplant late July for harvest before frost. Use cages; pinch suckers for bushier growth.
2. Cool-Season Greens: Spinach, arugula, mustard greens – sow August–early September. Choose fast-maturing varieties (e.g., ‘Bloomsdale’ spinach).
3. Root Crops: Turnips, radishes, beets – plant late July–August for harvest before October 15. Thin seedlings to 2–3 inches apart.
4. Garlic & Onions: Hardneck garlic (plant October) and short-day onions (sow July–August) – both store well and thrive in cool fall soil.

Don’t forget companion planting to maximize space and deter pests. Pair carrots with onions (repels carrot flies), tomatoes with basil (boosts flavor), and kale with thyme (improves growth). For urban gardens, use container-friendly crops like bush beans, lettuce, and radishes in 5–10 gallon pots.

Test your soil pH (ideal: 6.0–7.0) before planting and amend with compost or aged manure. In spring, add a balanced fertilizer (10-10-10) at planting; in fall, focus on organic matter to feed next year’s crops.

Mulch with straw or grass clippings to retain moisture and suppress weeds.

With these seasonal strategies, you’ll enjoy a bountiful harvest from spring greens to fall tomatoes—even in Seattle’s unpredictable climate. Happy planting! 🌿

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Month	Cool-Season Crops (Direct Sow)	Warm-Season Crops (Transplant/Start Indoors)	Soil Temp (°F)	Notes
February	Peas, spinach, lettuce	Start tomatoes, peppers indoors	40-50°F	Use row covers for frost protection
March	Carrots, radishes, kale	Transplant onions, broccoli	45-55°F	Harden off seedlings before transplanting
April	Beets, cabbage, Swiss chard	Direct sow beans, corn	50-60°F	Watch for late frosts; use cloches if needed
May	Successive plantings of lettuce	Transplant tomatoes, peppers	60-70°F	Wait until soil is consistently warm
June	None (heat-sensitive)	Sow cucumbers, squash	65-75°F	Mulch to retain moisture
July	Start fall broccoli indoors	Plant sweet potatoes	70-80°F	Begin succession planting for fall