Practical planning tools for short growing seasons.
Climate-based broccoli planting guide for Mount Vernon, Washington
When to Plant Broccoli in Mount Vernon
Broccoli is usually an easy fit in Mount Vernon. The season is generally not the hard part, so gardeners can focus more on quality, consistency, and harvest timing.
Typical Planting Window
Excellent fit in this climate
Use the planting dates below for broccoli in Mount Vernon.
Start indoors
February 3
Typical planting windowMarch 10 – March 24
MethodTransplant
Typical days to maturity60–75
Broccoli is usually started indoors around February 3 and planted outdoors during the normal local window of March 10 to March 24.
Most varieties need about 60–75 days to reach maturity once they are in the garden.
Broccoli is usually an easy seasonal fit in Mount Vernon. The more useful question is how to turn that margin into better sizing, steadier growth, and a cleaner finish.
Even in an easier climate, this crop still pays back uninterrupted growth. The season helps with maturity, but it does not erase the effects of checks that reduce sizing or finish quality.
Best local strategy:
Use the normal planting window, avoid growth checks, and keep moisture and spacing consistent so the crop sizes evenly.
Can Broccoli Mature in Mount Vernon?
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.
Available GDD (base 40)3878
Typical crop GDD target900
Heat margin+2978
From the usual planting window, Mount Vernon typically provides about 3878 growing degree days for broccoli. With a typical crop target of 900, that leaves a heat margin of +2978. 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.
Checkpoint
Remaining GDD
Heat margin
Fit vs typical target
Apr 15
3802
+2902
Comfortable
May 1
3631
+2731
Comfortable
May 15
3438
+2538
Comfortable
Jun 1
3144
+2244
Comfortable
Jun 15
2876
+1976
Comfortable
Jul 1
2553
+1653
Comfortable
How Different Broccoli Varieties Affect Results
Most broccoli varieties can succeed in Mount Vernon in a typical year. That gives gardeners room to choose for the kind of harvest they want, not just for minimum maturity speed.
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
Best Broccoli Varieties for Mount Vernon
Broccoli variety choice in Mount Vernon is mostly about head reliability, side-shoot production, stress tolerance, and how cleanly the crop fits the cool part of the season.
March 24
local season starts
November 3
frost pressure returns
Less heat used3878 GDD available
Hover or tap the dots to see which recommended varieties use that much local heat.
For Mount Vernon, start with Packman and Green Magic for broccoli when you want dependable early broccoli heads or strong early hybrid broccoli.
Choose De Cicco when you want flexible early broccoli and side shoots.
Look at Marathon and Belstar when you specifically want later broccoli plantings or reliable main-season broccoli.
Compare each variety’s heat need and maturity timing against the local frost-free window before choosing what to grow.
Recommended starting point
PackmanEarly
850 GDD needed3878 available before frost
March 24November 3
Comfortable fit
Why this fit?
Local season fit:
Packman leaves about 3028 GDD cushion against the normal Mount Vernon crop heat estimate.
Best for: dependable early heads.
A practical early broccoli with good short-season usefulness.
Tradeoff: Practical more than specialty.
Green MagicEarly
850 GDD needed3878 available before frost
March 24November 3
Comfortable fit
Why this fit?
Local season fit:
Green Magic leaves about 3028 GDD cushion against the normal Mount Vernon crop heat estimate.
Best for: strong early hybrids.
A strong early hybrid that often handles the main spring broccoli window well.
Tradeoff: Still needs cool growing conditions to finish well.
Fastest / most cushion
De CiccoVery early
750 GDD needed3878 available before frost
March 24November 3
Comfortable fit
Why this fit?
Local season fit:
De Cicco leaves about 3128 GDD cushion against the normal Mount Vernon crop heat estimate.
Best for: flexible early broccoli.
An early broccoli that is useful when gardeners want flexibility, side shoots, and a quicker harvest path.
Tradeoff: Heads may be less uniform than hybrid types.
Also realistic
MarathonLate
1050 GDD needed3878 available before frost
March 24November 3
Comfortable fit
Why this fit?
Local season fit:
Marathon leaves about 2828 GDD cushion against the normal Mount Vernon crop heat estimate.
Best for: later broccoli plantings.
A slower broccoli that is more exposed if spring is delayed or summer heat arrives early.
Tradeoff: More exposed if spring is delayed or summer heat arrives early.
BelstarMid-season
950 GDD needed3878 available before frost
March 24November 3
Comfortable fit
Why this fit?
Local season fit:
Belstar leaves about 2928 GDD cushion against the normal Mount Vernon crop heat estimate.
Best for: reliable main-season broccoli.
A productive broccoli that works well where the season gives a reasonable cool-weather runway.
Tradeoff: Needs more cool-season runway than early broccoli.
GDD comparisons are a planning shortcut, not a guarantee. Soil, watering, sowing depth, pests, transplant quality, and harvest goals still affect the final result.
Variety class
Typical days to maturity
Typical GDD need
Local fit
Very early
55–60
750
Good fit
Early
60–68
850
Good fit
Mid-season
68–78
950
Good fit
Late
78–90
1050
Good fit
Main risk: The usual setbacks here come from management choices rather than from the season itself.
How Frost Affects Planting Dates for Broccoli in Mount Vernon
Mount Vernon usually has about 224 frost-free days, with a typical last spring frost around March 24 and a typical first fall frost around November 3.
Typical last spring frostMarch 24
Typical first fall frostNovember 3
Typical frost-free days224
Minimum safe temperature28°F /
-2
°C
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.
The most common problems here are not climatic ones. Gardeners usually lose ground through timing, uneven growth, or letting the crop move past its best stage.
In Mount Vernon, broccoli usually has a solid seasonal margin when planted around March 17. The warmest garden spots are usually south-facing walls, sheltered gardens, raised beds, and sunnier urban lots. Cooler spots like low spots, exposed sites, and shadier yards tend to warm up later and usually provide less heat. For broccoli, warmer garden spots usually improve early growth and can make timing a little more forgiving.
Set up broccoli for steady growth and pest protection
The better results usually come from steady growth, pest protection, and avoiding early setbacks.
Transplant support
Strong young plants help avoid slow starts and uneven sizing.
