When to Plant Cauliflower in Thompson, MB
Cauliflower is a cool-season brassica that produces dense white, purple, or green heads called curds. It is more finicky than broccoli but rewards with a mild, nutty flavor.
Thompson, Manitoba is in USDA Zone 3b. The average last spring frost is May 25 and the first fall frost is September 29, giving you a growing season of approximately 127 days.
At an elevation of 728 feet, Thompson receives approximately 11.2 inches of rainfall annually with predominantly black chernozem soil. Summer highs average 66°F, so choose short-season varieties of Cauliflower to ensure they mature before fall. With low rainfall, drip irrigation is essential for growing Cauliflower successfully. Mulch heavily to conserve soil moisture.
Thompson Soil Profile
Soil Type
Black Chernozem
Soil pH
6.0-7.0
Drainage
Well Drained
Cauliflower 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.
How to Plant Cauliflower
Fall planting: Sow 12 weeks before your first frost date for a fall harvest.
How Much Cauliflower to Grow
For a family of 4, plant approximately 12 cauliflower plants in about 30 sq ft. In Thompson's 127-day season, you'll have plenty of time for a full harvest. Plan your garden layout →
Cauliflower Water Budget
Monthly Watering Guide for Cauliflower
Cauliflower needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Cauliflower Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 0.5" | 0" | ❄️ Dormant |
| Feb | — | 0.6" | 0" | ❄️ Dormant |
| Mar | — | 0.9" | 0" | ❄️ Dormant |
| Apr | — | 1.1" | 0" | ❄️ Dormant |
| May | 4.3" | 1.1" | 3.2" | 🚿 Regular watering |
| Jun | 4.3" | 1.4" | 2.9" | 🚿 Regular watering |
| Jul | 4.3" | 1.3" | 3" | 🚿 Regular watering |
| Aug | 4.3" | 1.1" | 3.2" | 🚿 Regular watering |
| Sep | 4.3" | 1.1" | 3.2" | 🚿 Regular watering |
| Oct | — | 0.9" | 0" | ❄️ Dormant |
| Nov | — | 0.7" | 0" | ❄️ Dormant |
| Dec | — | 0.6" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Thompson). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Cauliflower 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.
Cauliflower Planting Timeline — Thompson, MB
Cauliflower Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 13 | Apr 13 – Apr 27 |
| Transplant Outdoors | May 25 | May 25 – Jun 8 |
| Direct Sow | May 18 | May 18 – Jun 8 |
| Harvest | July 20 | Jul 20 – Sep 21 |
| Fall Sowing | July 7 | Jul 7 – Jul 21 |
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 | Transplant Outdoors Direct Sow |
| July | Fall Sowing Harvest |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · 1-2 times/week
📅 Days to Maturity
55–100 days
🧪 Soil pH
Needs 6–7 · Your soil: N/A
🗺️ USDA Zone
Zone 3b
📆 Growing Season
127 days in Thompson
Growing Tips for Cauliflower in Thompson
Common pests for Cauliflower in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
Thompson receives only 11" of rain annually. Cauliflower needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Start seeds indoors 6 weeks before transplanting. Blanch white varieties by tying outer leaves over the head. Provide consistent moisture and avoid temperature extremes.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Cauliflower in Other Locations
Frequently Asked Questions
When should I plant Cauliflower in Thompson, MB?
Thompson is in Zone 3b with an average last frost of May 25. Plan your Cauliflower planting based on this frost date — see the calendar above for exact timing.
What planting zone is Thompson, MB?
Thompson, Manitoba is in USDA Hardiness Zone 3b. The average last spring frost is May 25 and first fall frost is September 29.
Your Thompson Garden Planner — Free
A 22-page printable planner built for Thompson (Zone 3b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.