When to Plant Napa Cabbage in Roosevelt County, MT
May in Roosevelt County, Montana — your action list
Welcome to May in Zone 4a. These are the moves that will have the biggest impact on your growing season.
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Move napa cabbage from tray to bed
Frost risk is low now in Roosevelt County, Montana. If you've been covering beds overnight, you can stop.
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Sow napa cabbage where they'll grow
Keep the top inch of soil moist until germination — a gentle morning watering for 5–7 days does the job.
Get ahead of June
- Starting indoors: napa cabbage
- Fall sowing: napa cabbage
Napa cabbage forms tall, barrel-shaped heads with tender, crinkled leaves and a mild, slightly sweet flavor. It is the primary cabbage used for kimchi.
Roosevelt County, Montana is in USDA Zone 4a. The average last spring frost is May 17 and the first fall frost is September 18, giving you a growing season of approximately 124 days.
At an elevation of 7,123 feet, Roosevelt County receives approximately 19.8 inches of rainfall annually with predominantly loam soil. Summer highs average 78°F, so choose short-season varieties of Napa Cabbage to ensure they mature before fall. With low rainfall, drip irrigation is essential for growing Napa Cabbage successfully. Mulch heavily to conserve soil moisture.
Roosevelt County Soil Profile
Soil Type
Loam
Soil pH
6.7-7.7
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 Roosevelt County
How your county's soil matches Napa Cabbage's growing requirements.
Soil pH
Your soil pH (6.7–7.7) overlaps with Napa Cabbage's range (6.0–7.5), though not a perfect match.
Soil Texture
The loam soil in Roosevelt County is excellent for Napa Cabbage — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.7%). Annual compost additions will help Napa Cabbage.
How to Plant Napa Cabbage
Fall planting: Sow 12 weeks before your first frost date for a fall harvest.
Succession Planting Napa Cabbage
Sow every 6.3 weeks. Last sowing by Jul 05 to harvest before frost.
For a dedicated fall crop, sow by Jun 26.
Plant Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Napa Cabbage
Napa Cabbage needs approximately 1.5 inches of water per week (6.5" per month). Here's how your county's rainfall compares month by month.
| Month | Napa Cabbage Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.6" | 0" | ❄️ Dormant |
| Feb | — | 1.1" | 0" | ❄️ Dormant |
| Mar | — | 1.7" | 0" | ❄️ Dormant |
| Apr | — | 2" | 0" | ❄️ Dormant |
| May | 6.5" | 2.3" | 4.2" | 🚿 Regular watering |
| Jun | 6.5" | 1.5" | 5" | 🚿 Regular watering |
| Jul | 6.5" | 1.6" | 4.9" | 🚿 Regular watering |
| Aug | 6.5" | 1.9" | 4.6" | 🚿 Regular watering |
| Sep | 6.5" | 1.7" | 4.8" | 🚿 Regular watering |
| Oct | — | 1.8" | 0" | ❄️ Dormant |
| Nov | — | 1.4" | 0" | ❄️ Dormant |
| Dec | — | 1.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Roosevelt County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Napa Cabbage 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.
Napa Cabbage Planting Timeline — Roosevelt County, MT
Napa Cabbage Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 5 | Apr 5 – Apr 19 |
| Transplant Outdoors | May 17 | May 17 – May 31 |
| Direct Sow | May 10 | May 10 – May 31 |
| Harvest | July 12 | Jul 12 – Aug 16 |
| Fall Sowing | June 26 | Jun 26 – Jul 10 |
Plant 1" deep · 15" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors |
| May | Transplant Outdoors Direct Sow |
| June | Fall Sowing |
| July | Fall Sowing Harvest |
| August | Harvest |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
1.5"/week · 2-3 times/week
📅 Days to Maturity
55–75 days
🧪 Soil pH
Needs 6–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 4a
📆 Growing Season
124 days in Roosevelt County
Growing Tips for Napa Cabbage in Roosevelt County
Direct sow Napa Cabbage outdoors after May 17 in Roosevelt County when soil has warmed and frost danger has passed.
Common pests for Napa Cabbage in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
Roosevelt County receives only 20" of rain annually. Napa Cabbage needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Best grown as a fall crop. Direct sow in late summer, 60-70 days before first frost. Keep soil evenly moist. Bolt-resistant varieties are available for spring planting.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Napa Cabbage in Other Locations
Frequently Asked Questions
When should I plant Napa Cabbage in Roosevelt County, MT?
Roosevelt County is in Zone 4a with an average last frost of May 17. Plan your Napa Cabbage planting based on this frost date — see the calendar above for exact timing.
What planting zone is Roosevelt County, MT?
Roosevelt County, Montana is in USDA Hardiness Zone 4a. The average last spring frost is May 17 and first fall frost is September 18.
Your Roosevelt County Garden Planner — Free
A 24-page printable planner built for Roosevelt County (Zone 4a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.