When to Plant Sunflower in Grant County, WI
This month in Grant County, Wisconsin
Welcome to May in Zone 5a. These are the moves that will have the biggest impact on your growing season.
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Set out sunflower seedlings
Your last frost (April 28) has passed. These warm-season crops can handle outdoor soil now.
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Direct-sow sunflower
Your soil is 54°F — warm enough for these to germinate without babying.
A few tasks this May that'll pay off in June
- Starting indoors: sunflower
Sunflowers are tall, cheerful annuals grown for their edible seeds and as pollinator magnets. They come in sizes from 2-foot dwarfs to 12-foot giants.
Grant County, Wisconsin is in USDA Zone 5a. The average last spring frost is April 28 and the first fall frost is October 8, giving you a growing season of approximately 163 days.
At an elevation of 884 feet, Grant County receives approximately 37.9 inches of rainfall annually with predominantly silt loam soil. Summer highs average 81°F, so choose short-season varieties of Sunflower to ensure they mature before fall.
Grant County Soil Profile
Soil Type
Silt Loam
Soil pH
6.1-7.1
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 Grant County
How your county's soil matches Sunflower's growing requirements.
Soil pH
Your soil pH (6.1–7.1) is within Sunflower's preferred range (6.0–7.5).
Soil Texture
The silt loam soil in Grant County is excellent for Sunflower — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Sunflower.
Organic Matter
Organic matter is excellent (5.1%) — Sunflower will thrive.
How to Plant Sunflower
Succession Planting Sunflower
Sow every 8 weeks. Last sowing by Jun 30 to harvest before frost.
Plant Water Budget
Monthly Watering Guide for Sunflower
Sunflower needs approximately 0.5 inches of water per week (2.2" per month). Here's how your county's rainfall compares month by month.
| Month | Sunflower Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.7" | 0" | ❄️ Dormant |
| Feb | — | 1.9" | 0" | ❄️ Dormant |
| Mar | — | 2.3" | 0" | ❄️ Dormant |
| Apr | 2.2" | 3.4" | 0" | ✅ Rainfall sufficient |
| May | 2.2" | 4.3" | 0" | ✅ Rainfall sufficient |
| Jun | 2.2" | 5.2" | 0" | ✅ Rainfall sufficient |
| Jul | 2.2" | 4.4" | 0" | ✅ Rainfall sufficient |
| Aug | 2.2" | 4.4" | 0" | ✅ Rainfall sufficient |
| Sep | 2.2" | 3.1" | 0" | ✅ Rainfall sufficient |
| Oct | 2.2" | 2.6" | 0" | ✅ Rainfall sufficient |
| Nov | — | 2.9" | 0" | ❄️ Dormant |
| Dec | — | 1.8" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Grant County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Sunflower 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.
Sunflower Planting Timeline — Grant County, WI
Sunflower Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 3 | Mar 3 – Mar 17 |
| Transplant Outdoors | May 12 | May 12 – May 26 |
| Direct Sow | May 5 | May 5 – May 26 |
| Harvest | July 21 | Jul 21 – Sep 8 |
Plant 1" deep · 18" apart · Rows 30" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | — |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.5"/week · Natural rainfall sufficient
📅 Days to Maturity
70–100 days
🧪 Soil pH
Needs 6–7.5 · Your soil: ideal
🗺️ USDA Zone
Zone 5a
📆 Growing Season
163 days in Grant County
Growing Tips for Sunflower in Grant County
Direct sow Sunflower outdoors after April 28 in Grant County when soil has warmed and frost danger has passed.
Common pests for Sunflower in this region include aphids and slugs. Use row covers early in the season and inspect plants weekly.
General growing tips
Direct sow after last frost. Stake tall varieties in windy areas. Harvest seed heads when the back turns brown and seeds are plump. Dry heads upside down.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Sunflower in Other Locations
Frequently Asked Questions
When should I plant Sunflower in Grant County, WI?
Grant County is in Zone 5a with an average last frost of April 28. Plan your Sunflower planting based on this frost date — see the calendar above for exact timing.
What planting zone is Grant County, WI?
Grant County, Wisconsin is in USDA Hardiness Zone 5a. The average last spring frost is April 28 and first fall frost is October 8.
Your Grant County Garden Planner — Free
A 24-page printable planner built for Grant County (Zone 5a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.