When to Plant Broccoli in Washington
Published: April 21, 2026
Washington gardeners in Zone 4b have a 21-week frost-free window for broccoli (May 7 to October 1). Cool-season crops like broccoli do well here because the short, cool summers match the plant's temperature preferences naturally. This guide gives exact dates for Washington based on your local frost calendar.
Broccoli Planting Dates for Washington
| Start seeds indoors | March 26–April 2 |
| Last frost (average) | May 7 |
| Transplant outdoors | April 9–19 |
| Direct sow outdoors | April 9–19 |
| Expect first harvest | June 8 – June 28 |
| Fall crop start | July 23–August 2 |
| Fall harvest | September 21 |
| First fall frost (average) | October 1 |
Growing Broccoli in Washington's Climate
Washington's cold Zone 4b climate is close to ideal for broccoli. The cool springs and moderate summers match the plant's natural temperature preferences, producing crisp, sweet, slow-bolting harvests that hot-climate gardeners cannot grow.
The fall broccoli crop in Washington is often better than the spring crop. Plants mature as temperatures cool in September and October, concentrating sugars and tightening heads or roots. Light frost can improve flavor; hard frost signals harvest time.
Common broccoli pests to watch for in Washington include Cabbage Worm and Cabbage Looper. The first line of defense is companion planting: Onion and Garlic planted nearby discourage several of these pests by confusing host-plant identification or repelling adults before they can lay eggs. Weekly garden walks in the early morning catch problems when they're still manageable.
Broccoli Garden Calendar for Washington
| Month | Task | Notes |
|---|---|---|
| January | — | Dormant season |
| February | — | Dormant season |
| March | Start seeds indoors | Use grow lights; warm soil to 70–75°F for best germination |
| April | Transplant outdoors | Soil temp must be 40°F+; nighttime lows above 50°F |
| May ← | Harden off seedlings | Set seedlings outdoors 1–2 hours daily, increasing gradually |
| June | First harvest window opens | Broccoli begins producing 60–80 days after transplant |
| July | Fall crop planting | Transplant or direct sow for fall harvest before frost |
| August | — | Dormant season |
| September | — | Dormant season |
| October | First frost approaches | Harvest remaining broccoli; cover plants on frost nights |
| November | — | Dormant season |
| December | — | Dormant season |
Broccoli Growing Tips for Washington Gardeners
- •For spring: start indoors 6 weeks before last frost and transplant outdoors 4 weeks before last frost.
- •For fall: start indoors in summer — count 10 weeks back from your first fall frost date.
- •Washington's short growing season means start seeds indoors under grow lights — don't rely on windowsill light which produces leggy, weak seedlings that struggle outdoors.
- •Cover young transplants with floating row covers for the first 2–3 weeks outside. The 3–5°F of protection reduces frost damage risk and accelerates early growth.
- •Harvest heads before any yellow flowers open — once flowers show, flavor declines quickly.
Companion Planting for Broccoli in Washington
In Washington's cold climate, planting broccoli with Onion and Garlic helps deter pests and improve soil. Avoid planting near Tomato and Pepper, which inhibit broccoli growth through root chemistry or shared pest pressure. See the full broccoli companion planting guide for the complete list.
Broccoli Planting Dates by City in Washington
Top cities in Washington — select for city-level frost dates and planting calendars.
Frequently Asked Questions
When should I plant broccoli in Washington?
In Washington (Zone 4b), start broccoli seeds indoors around March 26–April 2 and transplant outdoors around April 9–19 — 4 weeks before the state's average last frost of May 7.
What is the last frost date in Washington?
Washington's average last frost date is May 7 in the state's most common Zone 4b. Frost dates vary by city — higher elevations and northern counties run 1 to 3 weeks later than the state average. See the city list below for city-level frost dates.
Can I grow broccoli year-round in Washington?
broccoli is a cool-season crop in Washington, with spring and fall windows. Summer heat bolts the plants before they can produce a harvestable crop. Succession planting every 2–3 weeks stretches the harvest window.
What broccoli varieties grow best in Washington?
For Washington's Zone 4b, De Cicco and Waltham 29 tolerate cold and produce secondary side shoots after main head harvest.
When do I start broccoli seeds indoors in Washington?
Start broccoli seeds indoors in Washington around March 26–April 2, which is 6 weeks before the state's average last frost of May 7. Use grow lights and keep soil temperatures at 70–75°F for fastest germination.