Sunflowers are a classic summertime flower that bring cheer with their bright yellow petals and tall, sturdy stalks Their versatility and hardiness make them a great addition to any Iowa garden. Knowing the best time to plant sunflowers in Iowa is key to getting a healthy crop of these iconic blooms
Why Grow Sunflowers in Iowa?
Sunflowers thrive in Iowa thanks to the state’s warm summers and fertile soil The flowers do well across most of the state, from the milder southeast to the cooler north Sunflowers are drought-resistant, so they can handle Iowa’s occasional dry spells in late summer. Once established, sunflowers can grow vigorously even through heat waves.
Tall sunflowers create an eye-catching backdrop in beds and borders. The flowers attract pollinators like bees and butterflies. After bloom, the seeds draw in songbirds. Sunflower seeds are edible, so some gardeners grow specific varieties just for the tasty seeds. With their versatility and hardy nature, it’s no wonder sunflowers are a popular crop for Iowa gardeners.
Iowa’s Growing Zones
Iowa has a few different growing zones that impact planting dates. The last spring frost dates range from early April in the southeast to early May in the northern counties. The first fall frosts hit between mid-October in the north to early November in the south.
Northern Iowa falls into USDA Hardiness Zones 4a and 4b. Central Iowa is mainly Zone 5a, while southern Iowa is Zone 5b. A sliver of counties along Iowa’s southern border fall into Zone 6a. Knowing your zone’s frost dates will help determine planting times.
When to Sow Seeds Outdoors
Sunflowers are not frost tolerant, so seeds should be sown after all chance of frost has passed. Planting too early may result in seeds rotting in cool, wet soil before they can germinate.
In Zone 4a, aim to sow seeds outdoors around May 5th. Zone 4b can plant starting around April 30th. Zone 5a can plant around April 25th, while Zone 5b can plant as early as April 10th. The southernmost Zone 6a can plant starting in early April.
If sowing in rows, wait 2-3 weeks after the last frost date. The soil will have warmed further, for better germination. Space rows 18-24 inches apart and seeds 6 inches apart within rows.
Starting Seeds Indoors
For a head start on the season, sow seeds indoors 4-6 weeks before the average last spring frost. Use biodegradable pots and seed starting mix. Provide strong light and grow seedlings at 60-70°F.
Harden off plants for 7-10 days before transplanting outdoors after all frost danger has passed. Take plants outside gradually to let them adjust to wind and sun. Transplant on a calm, cloudy day to reduce stress. Water well and provide shade for a few days after transplanting.
Direct Sowing Tips
Sunflowers can be directly sown into the garden once the soil has warmed. Prepare a seedbed free of weeds, rocks and clods. Rake soil smooth before sowing. Space dwarf varieties 12-18 inches apart and tall varieties 18-24 inches apart.
Sow seeds 1 inch deep. Plant 2-3 seeds together, then thin to the strongest seedling. Thin when plants have 3-4 true leaves. Water after planting and cover beds with netting to protect from birds.
Best Sunflower Varieties for Iowa
Many sunflower varieties grow well across most Iowa gardens. Some top picks include:
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Mammoth Grey Stripe – Large grey & white striped flower heads, grows 6-12 feet tall
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Autumn Beauty – Branching plant produces loads of 4-6 inch blooms, grows 4-5 feet
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Sunbright Supreme – Vibrant yellow petals with dark centers, dwarf variety under 3 feet
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Chocolate Cherry – Unique burgundy-red blooms, grows 5-6 feet tall
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Strawberry Blonde – Soft pinkish-orange blooms with yellow tips, 4-5 feet tall
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Russian Mammoth – Heirloom variety with giant seed heads, grows up to 12 feet
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Velvet Queen – Dark red blooms, ideal for cut flowers, 6-8 feet tall
Ongoing Care
Sunflowers are relatively low-maintenance once established. Water 1-2 inches per week if rain is lacking, more in extreme heat. Stake taller varieties if needed. Remove spent blooms to encourage more flower production. Leaving some flowers to go to seed provides food for birds.
With proper timing for sowing and planting, Iowa gardeners can enjoy a bountiful crop of cheerful sunflowers. Time your plantings based on the average frost dates for your growing zone. With little care needed, sunflowers will reward you with their bright blossoms and unique seed heads.
Planting, Growing, and Caring for Sunflowers
With bright blooms that go all summer, sunflowers are heat-tolerant, resistant to pests, and attractive to pollinators. Harvest the seeds in late summer and fall for a healthy snack, or feed them to the birds! Learn how to plant, grow, and care for sunflowers.
The sunflower (Helianthus annuus) is an annual plant with a sizeable daisy-like flower face. Its scientific name comes from the Greek words helios (“sun”) and anthos (“flower”). The flowers come in many colors (yellow, red, orange, maroon, brown), but they are commonly bright yellow with brown centers that ripen into heavy heads filled with seeds. Sunflowers make excellent cut flowers, and many attract bees, birds, and butterflies.
Sunflowers are heliotropic, which means that they turn their flowers to follow the movement of the Sun across the sky from east to west and then return at night to face the east, ready again for the morning sun. Heliotropism happens during the earlier stages before the flower grows heavy with seeds.
There are tons of varieties of sunflowers available today, so there’s bound to be one that fits your garden. Choose between those with branching stems or single stems, those that produce ample pollen for pollinators or are pollen-free (best for bouquets), those that stay small or tower above the rest of the garden, or those that produce edible seeds! Learn why you should start growing these happy flowers in your garden.
How Long Do Sunflowers Take to Bloom?
A reasonably fast-growing flower for its size, most sunflower varieties mature in only 70 to 95 days. The largest sunflower varieties grow to over 16 feet tall, while smaller varieties have been developed for small spaces and containers and rarely grow larger than a foot tall! The flower heads can reach over 12 inches in diameter within the large seeded varieties.
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First and foremost, find a sunny spot! Sunflowers grow best in locations with direct sunlight (6 to 8 hours per day); they require long, warm summers to flower well. Shelter from strong winds—for example, along a fence or near a building—helps as they mature. Larger varieties may become top-heavy, and a strong wind can topple them.
Choose a location with well-draining soil. The planting spot shouldn’t pool with water after it rains. Otherwise, sunflowers aren’t too picky about soil, but the soil shouldn’t be too compacted for the best results. They have long tap roots that need to stretch out; in preparing a bed, dig down or till 2 feet in depth and about 3 feet across. They’re not too fussy when it comes to soil pH, either. Sunflowers thrive in slightly acidic to somewhat alkaline soil (pH 6.0 to 7.5).
Sunflowers are heavy feeders, so the soil needs to be nutrient-rich with organic matter or composted (aged) manure. Or, work in a slow-release granular fertilizer 8 inches deep into your soil.
Plant sunflowers in a spot sheltered from strong winds, perhaps along a fence or building. Larger varieties may become top-heavy, and a strong wind can be devastating.
Before choosing a planting site, decide whether or not you want to grow a sunflower tower—a fun project for kids!
How to Grow Sunflowers at Home
FAQ
What is the best month to plant sunflowers?
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Timing:
- Sunflowers thrive in warm weather, so wait until the danger of frost has passed and the soil temperature is consistently above 50°F.
- In Southern California, this typically occurs around late March or early April.
- You can plant seeds directly into the garden or start them indoors and transplant them once they’re large enough.
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Soil:
- Sunflowers prefer well-drained soil.
- Amend the soil with compost or other organic matter to improve fertility and drainage.
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Sunlight:
- Sunflowers need at least 6-8 hours of sunlight per day.
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Spacing:
- Space sunflower plants according to their variety, typically 6-12 inches apart for smaller varieties and 2-3 feet apart for larger varieties.
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Watering:
- Water the plants regularly, especially during dry periods, but avoid overwatering.
When can you plant sunflowers in Iowa?
Planting sunflower can begin anytime after soils have warmed to 50 degrees F. (April) through mid-July.
Do sunflowers come back every year?
While most varieties of this bright beauty are annual sunflowers, meaning they will not come back the following growing season, they may self-germinate from dropped seeds if you leave the heads on the plants throughout the winter. The perennial Maximillian sunflower features small blooms in late summer and early fall.
Do I have to soak sunflower seeds before planting?
You can soak your sunflower seeds in water before you plant them if you want to, but it isn’t necessary. And if you do decide to soak them, don’t soak them for too long or they could drown! I recommend that you soak the seeds for 12–24 hours, and no longer than 48 hours.