Sunday, July 29, 2012

Hooray for Helianthus!

As summer heats up, Helianthus comes into its own.  The genus that gives us the stately annual sunflower, Helianthus annuus, is well represented in the southeastern US and most of the US itself. In fact, if there had to be only one wildflower to represent the US, I’d nominate the sunflower, it’s that ubiquitous.  According to one source there are 67 species native to the US, and USDA shows approximately 25 being found in Georgia. They are found throughout the state, including coastal areas.

Helianthus annuus

Vegetable gardeners love to grow the annual sunflower. I have seen a number of roadside plantings this year (gardeners thoughtfully put the sunflowers closest to the road so the rest of us can admire them). On the way back from vacation this year we passed a huge field of them; we stopped so that 3 of us could take pictures of them.

Cultivation has created some incredible cultivars, including the single-flowered giant plant that we admire so much. The non-cultivated (that is, the original) form actually is more branched and has multiple smaller flower heads on the plant.

Field of Helianthus annuus
Disk and ray flowers

Most of the members of the genus Helianthus are perennial plants. They usually share the characteristics of coarse, rough leaves and a flower that is composed of both disk and ray flowers. The disk flowers are tiny fertile flowers in the center – once pollinated, each flower turns into a single achene (or seed). The showy ray flowers are what we call the flower petals; the ray flowers are not fertile and are there to attract insects (and humans) to the flower.

Many species are “rhizomatous” - the plant increases over time by extension of underground roots; several of these are considered by most to be too aggressive for the average garden. It’s important to recognize this characteristic in any species being considered for a small space. One species even has edible roots – I’m sure many of you have heard of Jerusalem artichoke (Helianthus tuberosus). If you want to grow it, just get one of the tubers from a fellow gardener and you’ll have plenty of yellow flowers and edible tubers in no time.

Back of flower, Helianthus

Helianthus flowers look like some of the other summer blooming composites such as Silphium and Polymnia, and some may even resemble black-eyed Susan (Rudbeckia). As I pointed out on the post about Rudbeckia, examining the back of the flower can be very helpful in identification.

In the garden, Helianthus can be a welcome mid-to-late summer perennial. While most species are suitable for drier conditions, the wet-tolerant swamp sunflower (Helianthus angustifolius) is a beautiful addition to rain gardens and average moisture sites. In my area it is a tall plant that lights up a garden in mid-October. People stop to ask what it is!

Helianthus angustifolius
Towering over other plants - Helianthus angustifolius

I enjoy having these cheerful natives in my garden - here are some of the ones that I have:

Helianthus atrorubens
Helianthus decapetalus

Helianthus divaricatus

Helianthus atrorubens is known as the purpledisk sunflower or Appalachian sunflower. It is one of the few to have basal leaves and one that does not spread by roots according to my personal observation.

Helianthus microcephalus

Helianthus decapetalus is known as the thin-leaved sunflower. The leaves are not thick and coarse like most of the others. This is a very aggressive spreader.

Helianthus divaricatus is a more shade tolerant species, often growing on the edge of woodlands, spreading by roots to form a very linear colony. This especially robust looking one was growing in a field, however.

Helianthus microcephalus is known as small-headed sunflower; it often has multiple clusters of the small flowers blooming at once.

Another annual form is quite famous - Helianthus porterii is known as the "Stone Mountain daisy". Pictures of this plant are courtesy of my friend Karen who lives near Stone Mountain, GA.

Helianthus porterii
Helianthus porterii

Another good reason to have sunflowers is that birds love the seeds. Leave the spent flowers on the plant to attract songbirds throughout the fall and even into winter.


  1. I have angustifolius--even works in heavy clay soil! Love these!

  2. I hope to try Helianthus divaricatus soon, maybe try to start some from seed this winter. It grows wild along the river near our house and is looking great right now. They're so cheery and really light up a shady spot.

  3. Wonderful photos of the Helianthus Ellen. I didn't know that Georgia had so many species.

  4. Beautiful.

    I enjoy sunflower seeds too...I want to plant enough for me and the birds.