Is it a weed or a wildflower? A blessing or a curse? Everyone has an opinion (although only the Grump's is correct), but if you're looking for the showiest blooms of autumn -- those which routinely cause multi-car pileups in front of your house due to gawking motorists -- here they are.
The name? Helianthus angustifolius aka swamp sunflower or narrowleaf sunflower. Native to the eastern United States, this perennial puts on an autumn show like no other. One reason is that it produces masses of bright yellow blossoms up to 3 inches wide. Another is that in good soil, it can easily grow 8 to 12 feet tall.
Swamp sunflower is blooming right now in the South. The Grump is not alone in his judgment of its impact. Nancy Goodwin, creator of fabled Montrose Gardens in Hillsborough, North Carolina, places it prominently in her border. "When it blooms," she notes, "it's like turning on the lights." Here's a photo from her tropical border taken in late September just as the sunflowers are opening up.
So why do some people hate swamp sunflower? Because it won't stay put. It spreads aggressively by underground rhizomes and will quickly take over a garden if you let it. Plant one plant and next year you'll have 10. The year after that, you'll have 100.
The image below, taken in the Grump's garden, proves the point. I was given a single division some years ago and left it to its own devices. This is what it looks like today on the side of my house.
Beautiful? Yes. Problem? Could be, unless you belong to the Swamp Sunflower Society of America and dream of the day all ugly humans are supplanted by billions of swamp sunflowers.
Fortunately, there are easy ways to control the spread of this plant. For instance:
1. Swamp sunflower plants are easy to pull up and throw away. Just firmly grasp the stem next to the ground and yank. Nothing to it.
2. The wetter the soil is, the faster swamp sunflower spreads. Planting in regular or drier soil slows it down.
Another problem people have is that this plant grows so tall that strong winds and rain can break the stems. But the wise Grump knows how to prevent this. Wait until your swamp sunflowers grow to 4 feet tall and then cut them down to 2 feet. This will probably limit their ultimate height to 6-7 feet, but if that's too tall, cut them back again. Cut them back no later than July, though, so they have time to form lots of flower buds.
Where can you get swamp sunflower? Well, anyone who has it will gladly share some, I promise you. Niche Gardens is a good mail-order source. They offer 'Mellow Yellow' (NOT what you're thinking), featuring soft yellow blooms; and 'Gold Lace,' which grows shorter and spreads less rampantly than the species. Sunlight Gardens is another good source.
What Swamp Sunflower Likes
Light: Full sun
Soil: Moist; lots of organic matter; takes poor drainage
Pests: Powdery mildew
Growth Rate: Fast
Bloom Time: September, October
Where It Grows: Throughout the South, Zones 6 to 10