When To Plant In Seattle

Knowing when to plant in Seattle is the single most important factor for a successful garden. Our unique maritime climate, with its mild, wet winters and dry summers, creates a planting calendar that’s different from much of the country. This guide will walk you through the optimal timing for planting everything from veggies to perennials, helping you make the most of our long, productive growing season.

This heading is your cornerstone for the entire year. Seattle’s gardening year is defined less by frost dates and more by cool, moist springs and autumns bookending a dry summer. The last average spring frost is around March 15th, and the first fall frost is typically near November 15th, giving us a generous 8-month window. However, soil temperature and moisture are often more critical guides than the calendar alone.

Understanding Seattle’s Planting Zones

Seattle primarily falls within USDA Hardiness Zone 8b, with some microclimates reaching 9a. This means our average annual extreme minimum temperature is 15 to 20 degrees Fahrenheit. More useful for planting times, however, is our maritime influence. The Pacific Ocean keeps us cooler in summer and warmer in winter than inland areas.

Spring: Often cool and damp well into June (“Juneuary”). Warm-season crops planted too early will just sit and sulk.
Summer: Dry and mild, with peak heat in late July and August. Consistent watering is essential.
Fall: A second, often excellent planting season as rains return and soil stays warm.
Winter: Mild and wet, ideal for many hardy plants that go dormant or grow slowly.

Your Month-by-Month Planting Guide

Here’s a practical breakdown of what to plant and when in the Seattle area. Remember, these are guidelines—always observe your own garden’s microclimate.

January – February: The Early Start

This is planning and prep time. On a dry day, you can prepare garden beds by adding compost. Indoors, you can start seeds for slow-growing flowers and leeks. By late February, if the soil isn’t waterlogged, you can directly sow:

Peas (a Seattle classic)
Fava beans
Spinach and hardy greens
Onion sets and garlic (should have been planted in fall, but there’s still time for some types)

March – April: Spring Momentum

The main spring planting push begins. Soil begins to warm, and days lengthen. You can start planting cool-season crops outdoors, either from seed or starts.

Direct Sow: Radishes, carrots, beets, chard, more lettuce, and parsnips.
Transplant Starts: Broccoli, cabbage, kale, cauliflower, and early lettuce starts.
Plant: Bare-root roses, berries, and fruit trees. Plant seed potatoes around St. Patrick’s Day.

Keep an eye on the forcast for any late cold snaps and be ready to cover tender starts.

May – June: Transition to Summer

This is our busiest planting period. Danger of frost is virtually gone by mid-May. Now is the time for warm-season crops, but wait until soil is truly warm—above 60°F.

Early May: Transplant tomatoes, peppers, and eggplants into greenhouses or cold frames. Harden off seedlings.
Late May to June: Plant tomatoes, peppers, cucumbers, squash, beans, and corn directly in the ground. Sow basil and other heat-loving herbs.
Also Plant: Annual flowers like marigolds and zinnias after the last frost.

July – August: Summer Planting & Succession Sowing

Focus shifts to maintenance and succession planting. Keep harvesting to encourage production. For a continuous harvest, sow quick-maturing crops every few weeks.

Succession sow: beans, carrots, lettuce, and radishes.
In mid-to-late July, start seeds indoors for fall brassicas (broccoli, Brussels sprouts).
Plant starts of winter squash and pumpkins early in July so they mature by fall.

September – October: The Prime Fall Season

This is arguably the best planting time in Seattle. The soil is warm, rains are returning, and plants establish well without summer heat stress.

Transplant: Those broccoli, cauliflower, and kale starts you grew indoors.
Direct Sow: Spinach, arugula, mustard greens, and overwintering onions.
Plant: Cover crops (like crimson clover) in empty beds to protect soil over winter.
Also: This is the perfect time to plant perennials, shrubs, and trees. Their roots will grow all winter.

November – December: Wrapping Up & Overwintering

Putting the garden to bed and planning for next year. You can still plant garlic and shallots if you haven’t already. Protect tender plants with mulch. Many hardy greens, like kale and collards, will survive the winter with minimal protection, providing fresh harvests on milder days.

Key Factors for Perfect Timing

Beyond the month, always check these two conditions before putting anything in the ground.

1. Soil Temperature, Not Just Air Temperature

A warm day in April doesn’t mean the soil is ready. Seeds rot and plants stall in cold, wet soil. Invest in a simple soil thermometer. Here’s what to aim for:

40-50°F: Peas, spinach, kale.
50-65°F: Lettuce, carrots, beets, chard.
65°F+: Tomatoes, peppers, squash, beans, cucumbers.

2. Soil Readiness (The Squeeze Test)

Take a handful of soil from about 3 inches deep and squeeze it.

If water streams out, it’s too wet.
If it forms a tight ball that holds its shape, wait a few more days.
If it crumbles lightly or forms a ball that easily breaks apart, it’s perfect for working and planting.

Working soil when it’s too wet damages its structure, creating hard clods that can last all season.

Tips for Gardening in Seattle’s Climate

Use Season Extenders: Cloches, cold frames, and row cover are invaluable for getting a jump on spring and protecting crops into fall.
Mulch Heavily: Apply mulch in late spring after soil warms to conserve moisture during our dry summer and suppress weeds.
Choose Adapted Varieties: Select vegetable and flower varieties bred for cooler, maritime climates. They will perform much better.
Water Wisely: Deep, infrequent watering is key once summer drought sets in. Soaker hoses or drip irrigation are ideal.
Don’t forget to rotate your crops each year to prevent pest and disease buildup.

Common Planting Mistakes to Avoid

Even experienced gardeners can make these errors in our unique climate.

Planting Warm-Season Crops Too Early: Impatience leads to stunted tomatoes. Wait for warm soil, even if it’s June.
Ignoring Soil Prep: Our rains leach nutrients. Always amend beds with plenty of compost before planting.
Crowding Plants: Good air circulation is crucial to prevent fungal diseases in our damp springs. Follow spacing guidelines.
Missing the Fall Window: Don’t stop gardening in August! Fall planting is low-stress and highly productive.

FAQ: Planting in the Pacific Northwest

Q: When is it safe to plant tomatoes outside in Seattle?
A: The safe bet is after Memorial Day, or when nighttime temperatures consitently stay above 50°F. Using a wall or a black plastic mulch to warm the soil can give you a head start.

Q: Can I grow vegetables year-round in Seattle?
A: Absolutely! With the use of cold frames or simple covers, you can grow hardy greens like kale, spinach, and certain lettuces throughout the winter.

Q: What are the best flowers to plant for Seattle’s climate?
A: Many flowers thrive here. For early color, try pansies and primroses. For summer, dahlias, roses, lavender, and hardy geraniums are excellent, low-maintenance choices.

Q: When should I plant my pumpkin seeds for Halloween?
A: Plant pumpkin seeds directly in the ground in late May or early June. This gives them plenty of time to mature by October. Choose a variety with a days-to-maturity that fits our season length.

Q: Is it to late to start a garden in July?
A: Not at all! You can plant fast-growing crops like bush beans, lettuce, and radishes. It’s also the ideal time to start seeds for your fall broccoli and cauliflower harvest.

By aligning your gardening activities with Seattle’s natural rhythms, you set yourself up for a bountiful and rewarding garden. Pay close attention to soil conditions, embrace the long fall season, and choose plants suited to our mild, moist climate. With this timing guide in hand, you’re ready to plant with confidence throughout the year.