When to plant Broccoli in Denver County, CO
Denver County gardeners should plant Broccoli between April 30 and May 21 in spring. With Denver County's Zone 6a climate (last frost May 14), Broccoli needs 60–90 days to mature — plant by June 28 for a full harvest. A second sowing from July 18 to August 1 extends the harvest into fall.
When to Plant Broccoli in Denver County, CO
This month in Denver County, Colorado
Welcome to June in Zone 6a. These are the moves that will have the biggest impact on your growing season.
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Indoor seed-starting week for broccoli
You're about 13 weeks out from your last frost — the perfect window to get these germinating indoors.
A few tasks this June that'll pay off in July
- First harvests: broccoli
- Fall sowing: broccoli
Broccoli is a nutrient-dense cool-season crop that produces large central heads followed by smaller side shoots. It is one of the most popular garden vegetables.
Denver County, Colorado is in USDA Zone 6a. The average last spring frost is May 14 and the first fall frost is September 26, giving you a growing season of approximately 135 days.
At an elevation of 6,818 feet, Denver County receives approximately 20.5 inches of rainfall annually with predominantly loam soil. Summer highs average 85°F, providing good warmth for Broccoli during the growing season.
Denver County Soil Profile
Soil Type
Loam
Soil pH
6.4-7.8
Drainage
Well Drained
Broccoli Planting Risk Windows
Percentages indicate frost risk at transplant. The 70% safe window means there is a 30% chance of frost after transplant — suitable for cold-hardy crops or gardeners with frost protection. The 90% safe window is best for tender plants.
Soil Compatibility in Denver County
How your county's soil matches Broccoli's growing requirements.
Soil pH
Your soil pH (6.4–7.8) is more alkaline than Broccoli prefers (6.0–7.0). Add sulfur or peat moss to lower pH.
Soil Texture
The loam soil in Denver County is excellent for Broccoli — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.2%). Annual compost additions will help Broccoli.
How to Plant Broccoli
Fall planting: Sow 10 weeks before your first frost date for a fall harvest.
Succession Planting Broccoli
Sow every 6.9 weeks. Last sowing by Jun 28 to harvest before frost.
For a dedicated fall crop, sow by Jul 18.
Broccoli Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Broccoli
Broccoli needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Broccoli Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.4" | 0" | ❄️ Dormant |
| Feb | — | 1.2" | 0" | ❄️ Dormant |
| Mar | — | 1.8" | 0" | ❄️ Dormant |
| Apr | — | 2.4" | 0" | ❄️ Dormant |
| May | 4.3" | 2.3" | 2" | 💧 Light watering |
| Jun | 4.3" | 1.3" | 3" | 🚿 Regular watering |
| Jul | 4.3" | 1.8" | 2.5" | 🚿 Regular watering |
| Aug | 4.3" | 2.1" | 2.2" | 🚿 Regular watering |
| Sep | 4.3" | 1.8" | 2.5" | 🚿 Regular watering |
| Oct | — | 1.8" | 0" | ❄️ Dormant |
| Nov | — | 1.6" | 0" | ❄️ Dormant |
| Dec | — | 1.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Denver County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Broccoli Heat Requirements (GDD)
What are Growing Degree Days (GDD)?
Growing Degree Days measure the total warmth your plants receive during the growing season. Think of it as a "heat bank" — every day above 50°F deposits warmth that helps your plants grow.
Each plant needs a certain amount of accumulated heat to mature. If your county provides more GDD than the plant needs, it's a great fit. If it's close, you may want to choose faster-maturing varieties or start seeds indoors to get a head start.
Broccoli Planting Timeline — Denver County, CO
Broccoli Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 9 | Apr 9 – Apr 23 |
| Transplant Outdoors | May 14 | May 14 – May 28 |
| Direct Sow | April 30 | Apr 30 – May 21 |
| Harvest | July 16 | Jul 16 – Aug 27 |
| Fall Sowing | July 18 | Jul 18 – Aug 1 |
Plant 1" deep · 15" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors Direct Sow |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | Fall Sowing Harvest |
| August | Fall Sowing Harvest |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · 1-2 times/week
📅 Days to Maturity
60–90 days
🧪 Soil pH
Needs 6–7 · Your soil: too_alkaline
🗺️ USDA Zone
Zone 6a
📆 Growing Season
135 days in Denver County
Growing Tips for Broccoli in Denver County
Direct sow Broccoli outdoors after May 14 in Denver County when soil has warmed and frost danger has passed.
Common pests for Broccoli in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
Denver County receives only 20" of rain annually. Broccoli needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Start seeds indoors 6-8 weeks before last frost. Provide consistent moisture to prevent hollow stems. Harvest heads before yellow flowers appear.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Isolate 1/2 mile from other brassicas. Biennial — must overwinter roots.
Broccoli in Other Locations
Frequently Asked Questions
When should I plant Broccoli in Denver County, CO?
Denver County is in Zone 6a with an average last frost of May 14. Plan your Broccoli planting based on this frost date — see the calendar above for exact timing.
What planting zone is Denver County, CO?
Denver County, Colorado is in USDA Hardiness Zone 6a. The average last spring frost is May 14 and first fall frost is September 26.
When should I plant Broccoli in Denver County, CO?
In Denver County, CO, plant Broccoli after the last frost (around May 14) and before the first frost (around September 26). Best results when soil holds above 50°F.
What growing zone is Denver County, CO for Broccoli?
Denver County sits in USDA Zone 6a. Broccoli grows reliably in zones 2a through 11b, so it's a good fit here.
Can Broccoli grow in Denver County's climate?
Yes — Broccoli grows well in Denver County's temperate climate. Denver County averages a 135-day frost-free season, with last frost around May 14 and first frost around September 26.
Your Denver County Garden Planner — Free
A 22-page printable planner built for Denver County (Zone 6a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.