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The best time to plant basil in Washington State is after the last frost date has passed, typically between late April and mid-May.
Timing when to plant basil in Washington State really comes down to understanding your specific region, because our state has very different climate zones.
From the wetter western side to the drier, hotter eastern side, knowing when to plant basil in Washington State can mean the difference between lush plants and sad, wilted ones.
In this post, we’ll dig into the ideal windows for planting basil in Washington State, plus tips for getting your basil off to a strong start.
Let’s get growing.
When to Plant Basil in Washington State: The Short Answer
When to plant basil in Washington State depends on your local frost dates, but the general golden rule is to wait until soil temperatures reach at least 50°F (10°C).
Basil is extremely frost-tender, so even a light chill will turn those beautiful green leaves black and mushy.
For most of western Washington, including Seattle, Tacoma, and Olympia, the last frost usually happens between late March and mid-April.
That means you can safely plant basil outdoors from late April through early May.
On the eastern side of the state, places like Spokane and Yakima often see later frosts, sometimes into early May, so you’ll want to hold off until mid-May or even late May.
The key takeaway is to plant basil in Washington State when nighttime temperatures consistently stay above 50°F.
1. Check Your Local Frost Date First
Your exact planting time for basil in Washington State hinges on your zip code’s average last frost date.
A quick online search for your county’s frost date will give you a reliable window.
Once that date passes, you’re clear to start putting basil in the ground.
But don’t just rely on the calendar, always check the 10-day forecast before you transplant.
A sudden cold snap in early May is not unusual in Washington, so be ready to cover your basil with a row cover or old sheet if needed.
2. Soil Temperature Matters More Than Air Temp
Basil roots simply refuse to grow in cold soil, so when to plant basil in Washington State is really about the ground warming up.
Grab a soil thermometer and stick it two inches down in your garden bed.
If it reads below 50°F, wait a week and check again.
In many parts of western Washington, the soil can stay cool well into May because of all the cloud cover and rain.
To warm the soil faster, lay down black plastic or landscape fabric a couple of weeks before you plan to plant.
This simple trick can shave a week or two off your waiting time.
3. Start Seeds Indoors for an Earlier Head Start
If you want to get a jump on when to plant basil in Washington State, start your seeds indoors about 6 to 8 weeks before your last expected frost.
That means sowing seeds in late February or early March for most of the state.
Use a seed-starting mix and keep the trays on a warm heat mat set to around 70°F.
Basil seeds germinate quickly, usually within 5 to 10 days, and they’ll grow happily under a grow light or on a sunny windowsill.
Once those seedlings have their first set of true leaves, you can transplant them into larger pots until it’s time to go outside.
Harden them off for a week by setting them outside for a few hours each day, gradually increasing their time outdoors.
Regional Planting Windows for Basil in Washington State
Washington is a big state with wildly different microclimates, so let’s break down the ideal planting time for basil in Washington State by region.
Western Washington (Seattle, Bellevue, Tacoma, Olympia)
This region has mild, wet springs, so the soil warms up slowly and steadily.
Your sweet spot for planting basil outdoors is usually the first two weeks of May.
Because of the marine influence, frost can linger into early April, but by May, you’re generally in the clear.
However, expect cooler nights in the 40s, so consider planting basil in raised beds or containers where the soil warms faster.
A south-facing wall or fence can also create a warm microclimate for your basil.
Eastern Washington (Spokane, Richland, Wenatchee)
Over here, springs are drier but colder, with frost dates that can stretch into mid-May.
When to plant basil in Washington State’s eastern half? Aim for mid-May to late May.
The upside is that once summer hits, eastern Washington gets seriously hot, often exceeding 90°F.
Basil thrives in that heat, so you can actually push for a second planting in June if you want a continuous harvest.
Just be careful to water deeply because the dry air and intense sun will dry out the soil fast.
Coastal and Mountain Areas
If you live near the coast like Long Beach or up in the Cascades foothills, your growing season is shorter and cooler.
For coastal areas, planting basil in Washington State is best done in late May, once the ocean breezes have stabilized.
In mountain towns like Leavenworth or Winthrop, wait until June because frost can strike even in late spring.
Use containers in these spots so you can move your basil indoors or against a warm wall during chilly nights.
How to Plant Basil in Washington State for Best Results
Once you’ve nailed the timing, proper planting technique will keep your basil thriving all summer long.
Basil loves full sun, at least 6 to 8 hours per day, so pick the brightest spot in your yard.
Space your plants about 12 to 18 inches apart to allow for good air circulation, which prevents fungal diseases.
Mix in a generous amount of compost or aged manure into the soil before planting.
After planting, water thoroughly and add a layer of mulch like straw or shredded leaves to lock in moisture and keep roots cool.
Fertilize lightly every 3 to 4 weeks with a balanced organic fertilizer, but don’t overdo it on nitrogen or you’ll get lots of leaves with less flavor.
Pinch off flower buds as soon as you see them, because once basil flowers, the leaves turn bitter and the plant stops producing new growth.
So, When to Plant Basil in Washington State?
When to plant basil in Washington State really comes down to waiting for those consistently warm nights and warm soil.
For most gardeners, that means planting basil in Washington State between late April and late May, depending on your specific region.
Check your frost dates, warm your soil, and start seeds indoors if you’re eager.
Basil is forgiving once it’s happy, so give it that warm, sunny start and it will reward you with fragrant leaves all summer.
Now that you know exactly when to plant basil in Washington State, you can confidently add this aromatic herb to your garden plan.
Happy planting.