When to Plant Zucchini in Boulder County, CO
This month in Boulder County, Colorado
Your garden in Boulder County, Colorado is working on a schedule, even when you're not. Here's where you should be this May.
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Time to transplant zucchini
Water the tray well an hour before you transplant. Roots slide out cleanly and settle in faster.
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Seed zucchini outdoors
Sow every 2 weeks for a continuous harvest. A single big planting means a single big glut.
Before June arrives, get these ready
- Starting indoors: zucchini
Zucchini is an incredibly prolific summer squash that can produce an abundance of fruit from just a few plants. It is versatile in the kitchen from grilling to baking.
Boulder 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 7,657 feet, Boulder County receives approximately 22.2 inches of rainfall annually with predominantly loam soil. Summer highs average 86°F, providing good warmth for Zucchini during the growing season.
Boulder County Soil Profile
Soil Type
Loam
Soil pH
6.7-8
Drainage
Well Drained
Plant 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 Boulder County
How your county's soil matches Zucchini's growing requirements.
Soil pH
Your soil pH (6.7–8.0) overlaps with Zucchini's range (6.0–7.5), though not a perfect match.
Soil Texture
The loam soil in Boulder County is excellent for Zucchini — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Zucchini.
Organic Matter
Organic matter is moderate (2.3%). Annual compost additions will help Zucchini.
How to Plant Zucchini
Succession Planting Zucchini
Sow every 5.1 weeks. Last sowing by Jul 28 to harvest before frost.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Zucchini
Zucchini needs approximately 1.2 inches of water per week (5.2" per month). Here's how your county's rainfall compares month by month.
| Month | Zucchini Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.7" | 0" | ❄️ Dormant |
| Feb | — | 1.3" | 0" | ❄️ Dormant |
| Mar | — | 1.8" | 0" | ❄️ Dormant |
| Apr | — | 2.2" | 0" | ❄️ Dormant |
| May | 5.2" | 3" | 2.2" | 💧 Light watering |
| Jun | 5.2" | 1.6" | 3.6" | 🚿 Regular watering |
| Jul | 5.2" | 2" | 3.2" | 🚿 Regular watering |
| Aug | 5.2" | 2.1" | 3.1" | 🚿 Regular watering |
| Sep | 5.2" | 2.1" | 3.1" | 🚿 Regular watering |
| Oct | — | 1.9" | 0" | ❄️ Dormant |
| Nov | — | 1.4" | 0" | ❄️ Dormant |
| Dec | — | 1.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Boulder County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Zucchini 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.
Zucchini Planting Timeline — Boulder County, CO
Zucchini Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 9 | Apr 9 – Apr 23 |
| Transplant Outdoors | May 28 | May 28 – Jun 11 |
| Direct Sow | May 21 | May 21 – Jun 11 |
| Harvest | July 16 | Jul 16 – Sep 10 |
Plant 1" deep · 30" apart · Rows 42" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors |
| May | Transplant Outdoors Direct Sow |
| June | Transplant Outdoors Direct Sow |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1.2"/week · 2-3 times/week
📅 Days to Maturity
45–60 days
🧪 Soil pH
Needs 6–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 6a
📆 Growing Season
135 days in Boulder County
Growing Tips for Zucchini in Boulder County
Direct sow Zucchini outdoors after May 14 in Boulder County when soil has warmed and frost danger has passed.
Common pests for Zucchini in this region include squash vine borer and cucumber beetles. Use row covers early in the season and inspect plants weekly.
Boulder County receives only 22" of rain annually. Zucchini needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Direct sow after last frost. Harvest when fruits are 6-8 inches long for best flavor and texture. Check plants daily in summer as fruits can double in size overnight.
Recommended Zucchini Varieties for Boulder County
Quick-producing varieties for shorter seasons
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Zucchini in Other Locations
Frequently Asked Questions
When should I plant Zucchini in Boulder County, CO?
Boulder County is in Zone 6a with an average last frost of May 14. Plan your Zucchini planting based on this frost date — see the calendar above for exact timing.
What planting zone is Boulder County, CO?
Boulder County, Colorado is in USDA Hardiness Zone 6a. The average last spring frost is May 14 and first fall frost is September 26.
Your Boulder County Garden Planner — Free
A 24-page printable planner built for Boulder 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.