When to Plant Sunflower in San Juan County, CO
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.
San Juan County, Colorado is in USDA Zone 4a. The average last spring frost is June 18 and the first fall frost is September 8, giving you a growing season of approximately 82 days.
At an elevation of 7,539 feet, San Juan County receives approximately 20.1 inches of rainfall annually with predominantly loam soil. Summer highs average 82°F, so choose short-season varieties of Sunflower to ensure they mature before fall.
San Juan County Soil Profile
Soil Type
Loam
Soil pH
6.3-8
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.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Sunflower Planting Timeline — San Juan County, CO
Sunflower Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 16 | Apr 16 – Apr 30 |
| Transplant Outdoors | July 9 | Jul 9 – Jul 23 |
| Direct Sow | July 2 | Jul 2 – Jul 23 |
| Harvest | September 17 | Sep 17 – Nov 5 |
Plant 1" deep · 18" apart · Rows 30" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors |
| May | — |
| June | — |
| July | Transplant Outdoors Direct Sow |
| August | — |
| September | Harvest |
| October | Harvest |
| November | Harvest |
| December | — |
Growing Conditions
Sun
Full Sun (6-8+ hours)
Water
Low — drought tolerant
Days to Maturity
70–100 days
Soil pH
6 – 7.5
USDA Zone
Zone 4a
Growing Season
82 days
Growing Tips for San Juan County
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
Level Up Your Garden
Sunflower in Other Locations
Frequently Asked Questions
When should I plant Sunflower in San Juan County, CO?
San Juan County is in Zone 4a with an average last frost of June 18. Plan your Sunflower planting based on this frost date — see the calendar above for exact timing.
What planting zone is San Juan County, CO?
San Juan County, Colorado is in USDA Hardiness Zone 4a. The average last spring frost is June 18 and first fall frost is September 8.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help San Juan County gardeners in Zone 4a organize planting dates, track what's growing, and never miss a planting window.
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