What is the optimal time to plant sunflowers?
Written by
Julia Anderson
Reviewed by
Prof. Charles Hartman, Ph.D.Knowing when to plant sunflowers is critical for gardening success. Plant seeds 1-2 weeks after the last frost in spring, as long as the soil temperature is at least 50°F (10°C). This avoids frost-kill potential while providing warm soil for germination. Cool climate gardeners plant a few weeks in late May to June for natives and hybrids, and from early to mid-April for total greenhouse sunflowers. Warm-weather gardeners start in March.
Take a soil temperature reading at 4 inches deep consistently with a trustworthy thermometer at 9:00 AM. If soil temperatures are below 50°F, germination will be delayed several weeks. I take temperature readings from different locations in the garden, as the shaded area stays cooler. The adequate temperatures will allow for quicker root development.
Cold Zones (3-5)
- Plant late May after frost risk passes
- Use cold-tolerant varieties like Russian Giant
- Protect seedlings with row covers if nights dip below 40°F
Temperate Zones (6-7)
- Mid-April planting optimal
- Succession sow every 14 days until June
- Watch for late frosts in higher elevations
Warm Zones (8-10)
- Start seeds February-March
- Provide afternoon shade in extreme heat
- Plant fall crops September-October
To ensure blooms all season long, practice succession planting. Sowing new seeds every 10-14 days from spring through summer will yield flowers from July until the first frost. Each season, I mark planting dates on my calendar. Staggering sowing dates offers fresh blooms for cutting.
Use local agricultural extension information to monitor frost dates. Frost kills sunflower seedlings outright. Historical data indicate when it is safe to plant. I keep a garden journal that tracks the first and last frost each season; this personal data is even more accurate than historical data, particularly after several years.
Read the full article: When to Plant Sunflowers: Full Guide
