When to Plant Annuals in Wyoming – 2026
Published: April 27, 2026
Wyoming sits in USDA Zone 4b (population-weighted primary). Plant annuals in Wyoming from Late May through June. Average last spring frost: May 7; first fall frost: October 1; frost-free growing season: 147 days. The bloom season for annuals is summer through fall.
Annuals Planting Dates in Wyoming
Plant warm-season annuals (petunias, zinnias, impatiens, begonias) after last frost when soil reaches 15°C / 60°F. Cool-season annuals (pansies, snapdragons, alyssum) can be planted 2–4 weeks before last frost. Start from seed indoors 6–8 weeks before transplanting.
For Wyoming specifically, the recommended planting window is Late May through June. This window is based on the state's population-weighted USDA Zone 4b — but Wyoming spans multiple climate zones, so adjust based on your local conditions. Coastal, mountain, and inland areas within Wyoming can vary by 2 to 4 weeks from the state average. The 147-day frost-free growing season in Wyoming is about 5 months frost-free. classic cool-season lawn climate. minneapolis, and similar northern cities.
Always check current local forecasts before planting frost-sensitive species. The 'last frost date' is an average — actual frost can occur 2 weeks after the average date in cold years. For warm-season annuals (petunias, zinnias, marigolds), wait at least 1 week past the average last frost date to ensure consistently warm soil. For cool-season annuals (pansies, snapdragons), planting 2 to 4 weeks before last frost is appropriate.
Best Annuals Varieties for Wyoming
For Wyoming Zone 4b, choose varieties rated for your zone or one zone colder for reliable performance. Below are the top annuals cultivars suitable for Wyoming's climate.
Most popular bedding annual. Continuous bloom from late spring through frost. Sun, deadhead spent blooms (or use Wave or Supertunia self-cleaning types).
Direct-sow after last frost. Drought-tolerant, prolific bloomer through fall. Cut-flower champion. Powdery mildew resistant cultivars (Profusion, Zahara).
Standard shade annual. New Guinea types tolerate more sun. Continuous bloom through fall.
Sun or part shade depending on type. Wax begonias are nearly indestructible bedding annuals. Tuberous types prefer shade with cool nights.
Plant 2 to 4 weeks before last frost or in fall. Tolerate frost down to -7°C (20°F). Bloom during cool weather; die or decline in summer heat.
How to Plant Annuals in Wyoming
Sow method for annuals: transplant or direct. The practical steps below apply to Wyoming's climate and the typical first-year planting timeline.
- →Warm-season annuals: plant after last frost when soil reaches 15°C (60°F).
- →Cool-season annuals: plant 2 to 4 weeks before last frost or in fall (Zone 7+) for spring or winter color.
- →For earliest blooms, start seeds indoors 6 to 8 weeks before last frost; transplant after frost.
- →Choose full sun for most annuals (zinnias, marigolds, petunias) and part shade for shade-loving types (impatiens, begonias).
- →Space according to mature size — typically 25 to 30 cm (10 to 12 inches) for most bedding annuals.
- →Water at the base; avoid overhead watering which promotes powdery mildew on zinnias.
- →Apply slow-release fertilizer at planting; supplement with weekly liquid feeding during peak growth.
- →Deadhead spent blooms weekly to extend the flowering period (skip for self-cleaning Wave petunias and triploid marigolds).
Annuals Care Calendar for Wyoming
Spring (Wyoming last frost: May 7): The main planting window opens after last frost when soil reaches 10°C (50°F). For warm-season annuals, wait at least 1 week past last frost. Apply slow-release fertilizer at planting for first-season vigor.
Summer: Water consistently for the first month after planting; established plants need watering only during extended dry periods. Peak bloom for warm-season annuals.
Fall (Wyoming first frost: October 1): Final blooms before first frost — no fall planting recommended for warm-season annuals. Apply final mulch layer after first hard frost.
Winter: Most plants are dormant. Avoid foot traffic on frozen ground. Plan next year's plantings — order seeds and bare-root stock for spring.
Frequently Asked Questions about Annuals in Wyoming
When should I plant annuals in Wyoming?
Plant annuals in Wyoming from Late May through June based on the state's primary USDA zone (4b). Plant warm-season annuals (petunias, zinnias, impatiens, begonias) after last frost when soil reaches 15°C / 60°F. Cool-season annuals (pansies, snapdragons, alyssum) can be planted 2–4 weeks before last frost. Start from seed indoors 6–8 weeks before transplanting.
What USDA zone is Wyoming?
Wyoming spans multiple USDA zones, but the population-weighted primary zone is 4b. The state's average last spring frost is around May 7 and first fall frost around October 1, giving a frost-free growing season of about 147 days. Adjust planting dates based on your specific local microclimate — coastal, mountain, and inland areas within the state can vary by 2 to 4 weeks from the state average.
Which annuals varieties grow best in Wyoming?
For Wyoming (Zone 4b), choose varieties rated for your zone or one zone colder for reliable winter survival. Petunias (Petunia × hybrida) (All zones, warm-season) is widely planted across most US zones. Zinnias (Zinnia elegans) is another strong choice (All zones, warm-season). Match the variety to your specific microclimate and sun exposure for best results.