Want to upgrade your garden this year? Here’s everything you need to know about how to grow sunflowers, according to the experts.
When to Plant Sunflowers
According to Alice Raimondo, a horticulture consultant in the Horticulture Diagnostic Lab at the Cornell Cooperative Extension of Suffolk County, soil temps should hit about 60 degrees Fahrenheit —usually a few weeks after your last frost date—before you plant sunflowers from seed. This timeline varies by climate; warmer regions reach this point before cooler areas. Referring to your area’s hardiness zone can help determine exactly when to start planting. If you’re not sure, reference the seed packet or contact your local university extension office for advice. You can start sunflower seeds indoors and transplant them outside later, but you’ll need to begin earlier. “Some folks like to start sunflowers inside to keep their rows consistent, because you don’t know what will pop up if you stick them in the ground,” says Thomas Crawley, a gardener at the U.S. Botanic Garden in Washington, D.C. “Doing this four to six weeks before the last frost date in your area ensures they’ll be mature enough to transplant when the frost date has passed.”
How to Grow Sunflowers From Seed
Successfully growing sunflowers from seed in your outdoor garden requires a few important steps.
Caring for Sunflowers
Ensuring the right soil, water, and sun conditions can help your sunflowers sprout and thrive throughout the season.
Soil
Sunflowers, which are indigenous to the Americas, are quite forgiving when it comes to soil. “They don’t mind sandy or clay soils, or moderately acidic or alkaline soil,” says Crawley. One thing to keep in mind: Sunflowers are prone to root rot, so it’s important to protect their roots from water logging. Well-draining, loamy soil is your best bet; if your area’s soil isn’t well-balanced, consider amending it to achieve better drainage.
Water
Many varieties of sunflower are somewhat drought-tolerant, says Crawley—so while they need some moisture to grow, they can survive if you skip a watering or water less. Once your sunflower seeds germinate, Raimondo suggests spacing out your waterings until you get to the point of once-weekly watering. Allowing the roots to dry helps them develop a deeper root system, which can better support the stems of large varieties so they won’t flop over. Whether you water with a hose or rely on rain, Crawley says sunflowers typically need an inch of water per week. “If you have a rain gauge and you have a sprinkler turned on, you know you’re done when the gauge is filled an inch,” he says. Ideally, the first few inches of the soil should be moist.
Sun
Sunflowers prefer as much sun as possible—ideally, eight hours of full sun a day, and no fewer than six. That may mean it’s best to plant your seeds in a sunnier space than you’d planned. “Certain places in your yard get more sunlight than others, so if optimal plant health is your goal, sometimes you have to let the sun dictate where you plant rather than aesthetic preferences,” says Crawley.
