When to plant Kai Lan in Boulder County, CO
Boulder County sits in USDA Zone 6a. Plant Kai Lan between April 30 (after last frost on May 14) and May 21. A second sowing from July 18 to August 1 extends the harvest into fall.
When to Plant Kai Lan in Boulder County, CO
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Kai lan (Chinese broccoli) is a brassica grown for its thick, glossy stems and small flower buds. It has a slightly bitter, broccoli-like flavor essential in Cantonese cooking.
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 Kai Lan during the growing season.
Boulder County Soil Profile
Soil Type
Loam
Soil pH
6.7-8
Drainage
Well Drained
Kai Lan 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 Kai Lan's growing requirements.
Soil pH
Your soil pH (6.7–8.0) overlaps with Kai Lan's range (6.0–7.5), though not a perfect match.
Soil Texture
The loam soil in Boulder County is excellent for Kai Lan — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Kai Lan.
Organic Matter
Organic matter is moderate (2.3%). Annual compost additions will help Kai Lan.
How to Plant Kai Lan
Fall planting: Sow 10 weeks before your first frost date for a fall harvest.
Succession Planting Kai Lan
Sow every 5.1 weeks. Last sowing by Jul 28 to harvest before frost.
For a dedicated fall crop, sow by Jul 18.
Kai Lan Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Kai Lan
Kai Lan needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Kai Lan 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 | 4.3" | 3" | 1.3" | 💧 Light watering |
| Jun | 4.3" | 1.6" | 2.7" | 🚿 Regular watering |
| Jul | 4.3" | 2" | 2.3" | 🚿 Regular watering |
| Aug | 4.3" | 2.1" | 2.2" | 🚿 Regular watering |
| Sep | 4.3" | 2.1" | 2.2" | 🚿 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.
Kai Lan 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.
Kai Lan Planting Timeline — Boulder County, CO
Kai Lan 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 2 | Jul 2 – Jul 30 |
| Fall Sowing | July 18 | Jul 18 – Aug 1 |
Plant 0.5" deep · 6" apart · Rows 12" 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 |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/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 Kai Lan in Boulder County
Direct sow Kai Lan outdoors after May 14 in Boulder County when soil has warmed and frost danger has passed.
Common pests for Kai Lan in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
Boulder County receives only 22" of rain annually. Kai Lan needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Direct sow in spring or fall. Harvest when flower buds first appear but before they open. Cut stems at the base to encourage side shoots. Prefers cool weather.
Companion Planting
Good Companions
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Check more plant combinations with our Companion Planting Checker →
Kai Lan in Other Locations
Frequently Asked Questions
When should I plant Kai Lan in Boulder County, CO?
Boulder County is in Zone 6a with an average last frost of May 14. Plan your Kai Lan 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.
When should I plant Kai Lan in Boulder County, CO?
In Boulder County, CO, plant Kai Lan 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 Boulder County, CO for Kai Lan?
Boulder County sits in USDA Zone 6a. Kai Lan grows reliably in zones 2a through 11b, so it's a good fit here.
Can Kai Lan grow in Boulder County's climate?
Yes — Kai Lan grows well in Boulder County's temperate climate. Boulder County averages a 135-day frost-free season, with last frost around May 14 and first frost around September 26.
Your Boulder County Garden Planner — Free
A 22-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.