When to Plant Broccoli in Seattle

Can Broccoli Mature in Seattle?

Growing degree days measure how much useful warmth typically accumulates during the season. For broccoli, this helps estimate whether local heat accumulation is usually enough for the crop to reach maturity on time.

From the usual planting window, Seattle typically provides about 4722 growing degree days for broccoli. With a typical crop target of 900, that leaves a heat margin of +3822. That large heat margin means the crop usually has no trouble reaching maturity here. In practice, planting timing mostly affects how comfortably the crop sizes up and when harvest is ready, not whether the crop can finish.

When Is It Too Late to Plant?

If planting later than usual, this table shows how much growing degree day heat is still available from each point in the season. For broccoli, it is most useful for judging how much freedom you still have to plant for quality, finish, and harvest goals as the season moves along.

How Different Broccoli Varieties Affect Results

In Seattle, most broccoli varieties are usually realistic choices. Gardeners can often choose across the maturity range without giving up much day-to-day reliability.

Varieties that often fit well here include:

• De Cicco — an early broccoli often chosen where gardeners want flexibility and quicker harvest
• Packman — a dependable standard with good short-season practicality
• Green Magic — a strong early hybrid that often handles the main spring window well
• Belstar — productive and reliable where the season gives a reasonable cool-weather runway
• Marathon — more exposed if spring is delayed or summer heat arrives early

Main risk: The most common issue here is not climate but management: uneven growth, delayed planting, or harvesting outside the best quality window.

How Frost Affects Planting Dates for Broccoli in Seattle

Seattle usually has about 249 frost-free days, with a typical last spring frost around March 13 and a typical first fall frost around November 17.

Broccoli is generally lightly frost tolerant and temperatures below about 28°F ( -2 °C) can slow growth or damage plants.

Broccoli is usually tolerant enough of cool conditions that light frost is not the main concern. The more useful question is how early planting affects establishment and overall crop quality.

Setbacks here usually come from practical decisions rather than from season length: planting later than ideal, uneven growth, poor moisture management, or harvesting outside the best eating window.

In Seattle, broccoli already has plenty of seasonal room when planted around March 6. In practical terms, the best spots are usually south-facing walls, sheltered gardens, raised beds, and sunnier urban lots. Cooler spots like low spots, exposed sites, and shadier yards are more likely to stay cooler and be less forgiving. For broccoli, warmer local sites usually help the crop get established earlier and grow a little more steadily.