True natives: Why sunflowers thrive next to I-70 in the Colorado High Country

As locals, we are accustomed to explaining the curiosities of mountain life with ease. The lack of atmosphere creates a rich, lavender sky, along with a greater propensity for sunburns. This same atmospheric deficit results in a lower temperature for boiling water, therefore increasing cooking times in some instances. And yet …

Where do all those sunflowers next to the interstate come from?

Simply put: right here. They are native annuals, to be precise (i.e. flowers which grow from seed in the spring and shed new seeds in the fall as the bloom dies). Denyse Schrenker, horticulture and small acreage extension agent with the CSU Extension in Eagle, notes they are the same as the standard, domesticated sunflower, just a wild version. 

The Helianthus annuus, according to Nick Courtens, curator of plant collections at the Betty Ford Alpine Gardens, has adapted extremely well to the specific conditions alongside Interstate 70. They are sustained by run-off moisture from the road as well as heat from the asphalt. They also benefit from a lack of competition from other vegetation.

Crucial for this hearty flower is a disturbed environment, or disturbed soil, according to Courtens, Schrenker and Kallie Rand with Eagle County Vegetation Management. Rand mentioned she has noticed this along other asphalt paths in the valley, including the path from Vail to Dotsero, where sunflowers thrive along the pavement’s perimeter with plenty of run-off and agitated soil.

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Courtens explained that an important part of the growing process includes the bloom dropping its seed in an area that will contain the seed, such as a divot or small recess. Activities such as digging or snowplowing then help the germination process for next spring. Places towards the median, however, where the soil is less disturbed, are therefore less hospitable for the sunflower where other vegetation typically grows.

Schrenker also points out that run-off usually does not extend much farther than the area right next to the edge of the pavement — another reason why these flowers stick to the immediate side of the road and not the medians.

Both Courtens and Schrenker emphasized the flower’s efficient germination as one of its main strengths, along with its importance for the local ecosystem. They make a considerable amount of seed, which then spreads via birds, wind, etc. Over time, a seed bank builds up along the road and the sunflower establishes its dominance as roadside sovereign, Courtens said.

He then pointed out that roadside sunflowers are specifically well-adapted to the hot, dry and gusty conditions of the interstate in the sense that they are small, sturdy, and tend to break less than taller versions you might see in the fields or other areas. Seeds produced from the bloom in the fall then carry this information for the next round of flowers in the spring, allowing them to be prepared for conditions they will encounter. And while some elements of human activity (driving, etc.) may contribute to spreading the seeds, one thing is clear for all the experts: these flowers are simply good at growing, particularly along the highway. 

So why are there sunflowers and not columbines, or other wildflowers? Schrenker highlighted the environment once again; wildflowers like columbines would need more moisture and shade unafforded by such commuter environments. That said, other wildflowers still populate our highways, such as curly cup gumweed or yellow sweet clover. 

According to Courtens, the sunflower can outgrow other noxious weeds at times, such as sweet clover and thistles. Jered Morgan, who works in vegetation management for the Colorado Department of Transportation, noted that the state agency does not treat these native flowers as noxious weeds and does not plant them purposefully; they appear on their own. He has also noticed them near Rifle, Glenwood and southern areas surrounding Colorado Springs.

The flowers are important for wildlife, including pollinators and birds, while serving as excellent material for revegetation when needed.  Courtens emphasized native bees, which benefit from the flower and also prefer disturbed soil for making their nests.

Schrenker and Courtens also emphasized the flower’s importance for humans.  Hannah Rumble, community programs director with Walking Mountains Science Center, mentioned a possible correlation with Lady Bird Johnson’s (Lyndon B. Johnson’s wife) passion for preserving the beauty of America’s highways.  She supported cultivating wildflowers along interstates with the American Association of Nurserymen and was instrumental in passing Highway Beautification Act in 1965 (a bill focused on removing billboards and advertising from interstates, allowing scenic views to dominate the background).

The former first lady firmly believed clean, picturesque environments were extremely beneficial for everyone. While cursory research did not point to any direct link between Lady Bird Johnson’s efforts and the sunflowers along Colorado’s roadways, it would not be surprising if there were — especially given the considerable political activity in the valley (i.e. Betty Ford).

Yet the most significant testament to the sunflower’s importance and nativity is its cultivation by Native Americans. As Schrenker explains, they first domesticated the sunflower around 1000 BCE. Courtens also mentioned sunflower oil, which has become an important staple in the food industry and a handful of others. Recent scientific studies have analyzed the effect of using sunflower stems as a more sustainable ingredient in concrete, with promising results.

Returning to our original question, these sunflowers are true natives, well-adapted to harsh, petulant mountain conditions. Modern infrastructure poses not a challenge, but an opportunity to thrive. They adorn our interstates, liven our commute, offer green solutions for building materials, and are just as responsible for our scenery as those fourteeners.