When to Plant Sunflower in Belknap County, NH
May in Belknap County, New Hampshire — your action list
Each item below is timed to Belknap County, New Hampshire's frost dates and soil temperatures. Skip nothing, stress about nothing.
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Set out sunflower seedlings
Your last frost (May 3) has passed. These warm-season crops can handle outdoor soil now.
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Sow sunflower where they'll grow
Rake a smooth bed, make a shallow furrow, drop seeds at the spacing on the packet, water gently, walk away.
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.
Belknap County, New Hampshire is in USDA Zone 5b. The average last spring frost is May 3 and the first fall frost is October 11, giving you a growing season of approximately 161 days.
At an elevation of 764 feet, Belknap County receives approximately 48.5 inches of rainfall annually with predominantly silt loam soil. Summer highs average 87°F, providing good warmth for Sunflower during the growing season.
Belknap County Soil Profile
Soil Type
Silt Loam
Soil pH
4.8-6.8
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 Belknap County
How your county's soil matches Sunflower's growing requirements.
Soil pH
Your soil pH (4.8–6.8) is more acidic than Sunflower prefers (6.0–7.5). Add garden lime to raise pH.
Soil Texture
The silt loam soil in Belknap County is excellent for Sunflower — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (3.5%). Annual compost additions will help Sunflower.
How to Plant Sunflower
Succession Planting Sunflower
Sow every 8 weeks. Last sowing by Jul 03 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 | — | 3" | 0" | ❄️ Dormant |
| Feb | — | 3.4" | 0" | ❄️ Dormant |
| Mar | — | 4.4" | 0" | ❄️ Dormant |
| Apr | — | 3.9" | 0" | ❄️ Dormant |
| May | 2.2" | 3.9" | 0" | ✅ Rainfall sufficient |
| Jun | 2.2" | 4.7" | 0" | ✅ Rainfall sufficient |
| Jul | 2.2" | 4.9" | 0" | ✅ Rainfall sufficient |
| Aug | 2.2" | 4.8" | 0" | ✅ Rainfall sufficient |
| Sep | 2.2" | 3.8" | 0" | ✅ Rainfall sufficient |
| Oct | 2.2" | 4.4" | 0" | ✅ Rainfall sufficient |
| Nov | — | 3.8" | 0" | ❄️ Dormant |
| Dec | — | 3.6" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Oct in Belknap 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 — Belknap County, NH
Sunflower Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 8 | Mar 8 – Mar 22 |
| Transplant Outdoors | May 17 | May 17 – May 31 |
| Direct Sow | May 10 | May 10 – May 31 |
| Harvest | July 26 | Jul 26 – Sep 13 |
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: too_acidic
🗺️ USDA Zone
Zone 5b
📆 Growing Season
161 days in Belknap County
Growing Tips for Sunflower in Belknap County
Direct sow Sunflower outdoors after May 03 in Belknap 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 Belknap County, NH?
Belknap County is in Zone 5b with an average last frost of May 3. Plan your Sunflower planting based on this frost date — see the calendar above for exact timing.
What planting zone is Belknap County, NH?
Belknap County, New Hampshire is in USDA Hardiness Zone 5b. The average last spring frost is May 3 and first fall frost is October 11.
Your Belknap County Garden Planner — Free
A 24-page printable planner built for Belknap County (Zone 5b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.