Penstemon Flowers and the Timing of Garden Beauty Under Water Stress

How might some of our favorite native garden plants respond to water stress as temperatures increase and precipitation events become harder to predict? This summer our team continued research started at Chatfield Farms by graduate student Brielle Cerep-Funke, who explored first-year establishment and growth of six Penstemon species under varying degrees of water availability (ranging from the Front Range–recommended amount of two inches of supplemental irrigation per month, down to half that amount, as well as no supplemental irrigation).

We wanted to know how these different watering regimes might affect the timing (phenology) of plant flowering and fruiting, as well as the overall amount of flowers and fruits present. Exploring this question has both fundamental biological implications for understanding plant-pollinator and drought dynamics, as well as practical implications for gardeners. 

By tracking six species of Penstemon, we can assess whether the timing of peak flowering (and therefore pollinator resource availability, as well as peak beauty in your garden!) is similar or different across species. We can also test whether increasing water stress affects all species in the same way, such as shifting flowering and fruiting to be earlier, or whether some species are more resistant to phenological shifts under drought. For example, we can hypothesize that some arid-range species—like Penstemon eatonii (firecracker Penstemon) and Penstemon palmeri (Palmer’s Penstemon)—might not shift their flowering phenology, even under the most limiting water conditions, while a higher-water species like Penstemon virens (Front Range beardtongue) could be more sensitive to increasing drought stress. 

We also thought it would be informative to push a range of species to their irrigation limits, including no supplemental irrigation to support initial establishment. As water resources across Colorado become increasingly limiting, having species-specific irrigation prescriptions can help increase water-use efficiency in our outdoor green spaces.

Stay tuned, as the data crunching now begins. In the meantime, enjoy some fun pictures of pollinators visiting our experimental plants.