Homegrown Habitat, September 2024: Sunflowers
Spiraling seeds on the head of a sunflower. (By Anna Benczur – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=45294283)
September 26, 2024—Sunflowers can be called the “festive food wagons” of the late-season garden, or maybe the “mathematical geniuses,” if you’re into Fibonacci’s sequence. Sarah Middeleer explains that they produce an abundance of food for caterpillars, pollinators, and birds, and that their seeds and florets grow in an amazing spiral pattern. You probably have seen this, if you grow them. Let us know about the wildlife they benefit. We also love reader photos. Drop us a line at habitat@ctaudubon.org.
Sunflowers are among the most valuable native plants for habitat-oriented gardening. This genus, Helianthus, part of the Asteracea family, originated in North and South America. Between 50 and 70 species sunflower are native to North America.
Sources vary, however, on which species of Helianthus are truly native to Connecticut and New England. For example, it is believed that the annual sunflower may have originated on the Colorado Plateau and is considered by some sources to be native only as far east as the Mississippi River. But it can be found growing wild in all of the lower 48 states. Sunflower even appears in the Iroquois creation myth. Native American tribes probably helped to distribute sunflower seeds in their travels and are thought to have bred sunflowers.
Dan Jaffe Wilder, director of applied ecology at Norcross Wildlife Foundation, recently made a rather sensible statement about nativity. In a talk to the Native Plant Society of New Jersey, Wilder said that he doesn’t pay as much heed to whether a plant is native to a particular county or state, but more to how much ecosystem value the plant provides. If the plant supports many caterpillars, pollinators, and birds, it passes his test even if the plant may only be considered truly native to another locale in the same region.
I’ll briefly discuss the annual sunflower, which was almost certainly introduced in Connecticut—but well before colonists arrived—and two perennial species considered endemic to Connecticut: thin-leaved and hairy sunflowers.
Common sunflower (Helianthus annuus) is the ancestor of the annual sunflower seeds we see for sale each spring. This plant produces smaller flower heads than some of the cultivars (cultivated varieties), but they are all closely related. One note of caution: when selecting seeds, avoid those that claim to be pollenless. They will be useless to wildlife.
The sunflower has two different types of flowers: ray and disc. The bright yellow ray flowers look like petals, but each one is an individual blossom. Inside the ring of ray flowers are the tiny disc flowers (called florets), which develop into seeds. Those closest to the ray flowers open first.
A remarkable factoid about sunflower florets and seeds is that they grow in spirals based on the Fibonacci sequence, in which each number is the sum of the two preceding numbers. Many things in the natural world are formed in this way, such as pine cones, some roses, and the chambered nautilus.
Thin-leaved sunflower is a good choice for the woodland edge, shade garden, meadow, and rain garden. (By sonnia hill – https://www.flickr.com/photos/18453498@N07/51389977479/, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=130117899)
In the case of the sunflower, the sequence allows the spirals to continue growing as the flower heads mature and the seeds develop, which permits the maximum number of seeds possible.
A U.S. Forest Service article on common sunflower further elaborates : “The fruits are arranged in two groups of spirals, one to the left and one to the right ….If one counts the number of left hand spirals, and then the number of right hand spirals, the two numbers will be neighbors in the series (typically 21 / 34, 34 / 55, or 55 / 89).
Sunflowers produce an abundance of food for caterpillars, pollinators, and birds. The entire Helianthus genus supports many specialized native bees. Two species cited by the National Wildlife Federation as endemic to Connecticut are caterpillar host plants to 58 species of moths and butterflies. Unfortunately, deer too will browse some sunflower species.
Sunflowers are also an important food source for seed-eating birds, including fall migrants. They particularly benefit goldfinches, whose young fledge late in the season just as the seeds are ripening. Sunflower seeds are also enjoyed by Mourning Doves, American Crows, many sparrows, meadowlarks, titmice, chickadees, White-breasted Nuthatches, and more.
Thin-leaved sunflower is a perennial species that spreads by rhizomes, so try to give it plenty of room (or hard edges like pavement or walls to contain it). This sunflower takes full sun or part shade in moist but well-drained, loamy soils. Its three-inch yellow flowers bloom on erect, purple, five-foot stems from July to October. The Native Plant Trust calls it a “pollinator powerhouse plant” that is of extremely high value to wildlife. It is a larval host plant to the silvery checkerspot butterfly.
Thin-leaved sunflower is a good choice for the woodland edge, shade garden, meadow, and rain garden.
Hairy sunflower attracts many types of native bees, other insects, and beetles. Like other sunflowers, it is an important nectar source for migrating monarchs and other butterflies. (By Jason Hollinger – Hairy SunflowerUploaded by Amada44, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=24216583)
Hairy (or rough) sunflower is also perennial. It hasn’t been recorded in any New England states except Connecticut. It indeed has rough, hairy stems, which contribute to deer resistance, that grow between 2.5 and six feet tall. (A trick to controlling height is to cut the plants back by one-third early in the season. They will grow significantly shorter but will bloom a bit later). It too forms dense colonies, spreading by both seeds and rhizomes.
Hairy sunflower normally grows in medium to dry soils in sunny areas but can take some shade. Each plant will be covered in multiple, bright-yellow flower heads that appear from July to October and often stay in bloom for a month or more. This sunflower is also attractive to many types of native bees, other insects, and beetles. Like other sunflowers, it is an important nectar source for migrating monarchs and other butterflies. One author recommends this plant for hillsides in need of erosion control.
The many human uses of sunflowers extend well beyond gardens, food, and oil. Sunflower is a heavy feeder and can thus be used to reduce excess nutrient load in post-agricultural sites where weeds might otherwise thrive. It also has allelopathic effects (compounds that can inhibit the growth of other plants), which can also help rid a site of weeds. Sunflower leaf extract has even been used as an herbicide. It is widely used in site remediation because sunflower can absorb heavy metals and may also help cleanse soil of antibiotics.
Unfortunately it may be far more difficult to obtain native sunflowers than the cultivars, but look for native plant nurseries and also sellers of native seeds. Organizations such as The Native Plant Trust and local conservation organizations may be good sources of native sunflowers as well.
Winter seed sowing is a fascinating project well explained by the Wild Seed Project’s website. I’ve tried it for two years running and have had good germination rates.
Sources
Dan Jaffe Wilder, “Building Resilient Landscapes,” Native Plant Society of New Jersey webinar, Sept. 18, 2024
Laura Erickson, 100 Plants to Feed the Birds Turn Your Home into a Healthy Bird Habitat, Storey Publishing, 2022
Jared Rosenbaum, Wild Plant Culture A Guide to Restoring Edible and Medicinal Native Plant Communities, New Society Publishers, 2023
https://www.fs.usda.gov/wildflowers/plant-of-the-week/helianthus_annuus.shtml
https://www.ams.org/publicoutreach/posters/fibonacci-poster-sm.pdf
https://www.evergreenseeds.com/where-are-sunflowers-native-to/
https://gobotany.nativeplanttrust.org/species/helianthus/annuus/
https://science.howstuffworks.com/math-concepts/fibonacci-nature.html
https://www.backyardecology.net/rough-sunflower/
https://nativeplantfinder.nwf.org/Plants/1561
https://plantfinder.nativeplanttrust.org/plant/Helianthus-decapetalus#Refs
https://newmoonnursery.com/plant/Helianthus-decapetalus
https://www.illinoiswildflowers.info/savanna/plants/tp_sunflower.htm
