As an Iowan gardener, I love growing towering sunflowers to add cheer and beauty to my landscape. Their bright, happy faces evoke summer days and attract pollinators to my yard.
But to get the most out of these sun-loving annuals it’s important to know the optimum time for planting sunflower seeds in Iowa’s variable climate.
In this article, I’ll share tips on when and how to successfully plant sunflowers in Iowa for a bountiful summer harvest
Sunflower Growing Conditions in Iowa
While sunflowers are quite adaptable, there are a few basic conditions they need to thrive in the Hawkeye State:
- Full sun exposure – At least 6-8 hours per day
- Fertile, well-drained soil – But not heavily compacted
- Neutral soil pH – Between 6.0-7.5
- Long, hot growing season – With temperatures above 50°F
- Protection from strong winds – Stake plants if needed
Sunflowers are heavy feeders that benefit from nutrient-rich soil amended with compost or manure. Their long taproots also need room to stretch out, so prepare the soil by tilling down 12-24 inches.
When to Sow Sunflower Seeds Outdoors in Iowa
Sunflowers are extremely sensitive to frost and cold soils. Wait until the danger of spring frost has completely passed before direct sowing them outside.
In most parts of Iowa, it’s generally safe to begin planting sunflower seeds directly in the garden anytime from mid-April through mid-June.
Iowa’s last expected frost dates range from:
- Northern Iowa – May 5-15
- Central Iowa – April 30 – May 10
- Southern Iowa – April 15-25
For best results, wait 1-2 weeks after your area’s average final spring frost date to sow seeds. This allows the soil to warm thoroughly.
Aim for soil temperatures above 50°F before planting. You can use a soil thermometer to check the temperature at planting depth.
Tips for Planting Sunflowers in Iowa
Follow these tips to successfully plant sunflowers in Iowa:
- Start seeds 1-1.5 inches deep – About 6 inches apart in rows spaced 2-3 feet apart
- Prepare soil well – Dig down 12-24 inches and mix in compost or manure
- Plant in full sun – Choose a spot with at least 6 hours of direct sunlight
- Shelter from wind – Situate seeds along fencelines or buildings
- Water regularly at first – Until seedlings are established
- Add fertilizer – Use a balanced organic fertilizer to encourage strong roots
- Plant successionally – Sow seeds every 2-3 weeks until mid-July for continuous blooms
I like to stagger my sunflower plantings from mid-April through mid-July. This spreads out the workload and also provides fresh flowers over a longer period.
Planting the giants in April and May allows time for their long maturation. Then I sow shorter varieties in June and July for late summer cheer.
Best Sunflower Varieties for Iowa
With hundreds of sunflower cultivars to choose from, it can be difficult deciding which are best suited to Iowa’s conditions.
Here are some top sunflower varieties to grow in the Hawkeye State:
Tall Sunflowers
- American Giant – Huge 15′′ yellow blooms on 14′ stalks
- Kong – Giant golden yellow single heads on 12′ plants
- Mammoth Russian – Heirloom with 12-16′′ yellow flowers on 12′ stems
- Paul Bunyan – Sturdy 13-15′ plants produce massive yellow blooms
Mid-sized Sunflowers
- Autumn Beauty – Multi-colored 6″ blooms on 7′ branching stems
- Ring of Fire – Unique 4-5′ bicolor variety with red-yellow petals
- Soraya – 5-6′ plants with bright orange 4-6″ blossoms
- Strawberry Blonde – 6′ rose-pink flowers with great vase life
- Sunrich Gold – 5′ pollen-free yellow blooms perfect for cutting
Dwarf Sunflowers
- Elf – Cheery 1-2′ yellow flowers with 4″ diameter
- Pacino – Early blooming 18″ variety ideal for containers
- Sungold – 2-3′ double yellow blooms on branching stems
- Sunset – 3′ bicolor with dark burgundy petals and yellow tips
- Teddy Bear – 2-3′ double yellow flowers on sturdy branching stems
When to Harvest Sunflowers in Iowa
Sunflowers take 70-95 days from seed to full bloom depending on the variety. Monitor your plants closely as they near maturity.
The heads are ready for harvesting when the back of the flower is yellow or brown, the petals are drooping, and the center seeds are plump.
Cut the mature heads with scissors or pruners, leaving about 6 inches of stem below the flower.
You can hang entire heads upside down in a dry spot to collect seeds. Or carefully rub seeds off dried heads into a container.
Rinse and dry seeds well before roasting or storing.
Enjoy a Summer Sunflower Harvest
With proper timing and care, it’s easy to grow a bountiful crop of sunny sunflowers in Iowa for cutting, wildlife habitat, or seed harvest.
Just be sure to wait until after the danger of frost, prepare the soil, select adapted varieties, and plant successively for waves of cheerful color from midsummer into fall.
The bright blooms and robust plants will withstand Iowa’s hot, humid summers while attracting pollinators and songbirds to your landscape.
How to Grow Sunflowers Successfully At Home
FAQ
What is the best month to plant sunflowers?
What not to plant with sunflowers?
Do sunflowers come back every year?
How long do sunflowers take to grow?
When should you plant sunflower seeds?
It’s best to sow sunflower seeds directly into the garden (or outdoor containers) after the danger of spring frost has passed, anytime after soils have warmed to at least 50°F (10°C). In the northern half of the U.S. and in Canada, this will fall between April and mid-June. In the South, this will probably occur in mid-March or early April.
When can you direct sow sunflowers?
Wait until the soil temperature is at between 50 to 60 degrees to direct sow sunflowers. In the southern United States, this can happen as soon as early March, or as late as mid-June in regions like New England or the Upper Midwest. With their large seeds, sunflowers are easy to direct sow.
When can you plant a vegetable garden in Iowa?
Planting in Iowa can start in March and ends in November. What garden, exactly, are they talking about? I know, I know. They’re probably talking about their vegetable garden, with warm-season annuals like tomatoes, peppers, squash, cucumbers. Seedlings of those are typically planted outdoors at the same time in late spring.
How far apart should sunflowers be planted?
Sunflowers should be planted 1 to 1½ inches deep and about 6 inches apart after the soil has thoroughly warmed. If you wish, you can plant multiple seeds and thin them to the strongest contenders when the plants are six inches tall. Give plants plenty of room, especially for low-growing varieties that will branch out.
