Perennials

Phlox – A Perennial for Pollinators

Phlox paniculata

During the dead of winter, our senses long for the summer ahead. I use this time of the year to plan the new plant additions to my garden. This summer, it’s going to be the garden phlox ‘Jeana’.

Why ‘Jeana’? The Trial Garden of Mt. Cuba Center in Delaware recently published results revealing the best of the best garden phlox. The cultivar? Phlox paniculata ‘Jeana’. What’s more, not only did ‘Jeana’ perform overall for many factors including resistance to powdery mildew, ‘Jeanna’ ranked highest in butterfly activity by a large margin!

Mt. Cuba Center Trial Garden Phlox

If you are not familiar with the native trial garden of Mt. Cuba Center, set in the rolling hills of the Delaware Piedmont, just minutes from Wilmington, Delaware, I’m pleased to introduce you. If you are familiar with Mt. Cuba, I’m happy to share the valuable ecological information from their latest research reports. This information is incredibly useful to Mid-Atlantic gardens as we amp up pollinator activity.

The focus of the trial garden is with the home garden in mind. Perennial plants are trialed for three years to ensure the plants experience a variety of weather conditions. In the first year, plants are watered to get established, just like we need to do in our home gardens. Afterward, the trial plants receive no supplemental water. Also, the trial is fungicide and pesticide-free.

Each plant trial is evaluated weekly and assigned a rating based on a scale of 1-5. Many factors go into account for the rating including, habit, floral display, disease resistance, hardiness, and foliage quality. The average of these weekly ratings is used to calculate the final score for that specific plant trial. For the garden phlox study, participants were also evaluated for ecological value, specifically butterflies over the last two years of the three-year trial.

More About Phlox

Phlox were some of the earliest plants discovered by European naturalists in America, and with one look at our summer garden phlox, the species Phlox paniculata, it’s obvious why—the tubular, pink-purple to white florets stand out. Today, there are many more colors and sizes to choose; the Mt. Cuba trial narrows down the choices, in particular, if you are looking for a garden phlox with powdery mildew resistance and the best butterfly activity.

Garden phlox are particularly susceptible to powdery mildew, a foliar disease. Powdery mildew is typically just a cosmetic issue, yet in severe cases, the foliar disease can cause significant defoliation and even plant death. Moreover, given there were hundreds of garden phlox planted in one location, powdery mildew was exceptionally severe. This severity had its advantages by identifying the truly superior cultivars.

The mildew results are helpful indeed, yet more and more of us want to know the wildlife benefits of the plants we grow. Frequently listed as a butterfly magnet, garden phlox is a must-have in our wildlife gardens. Sugary nectar fills the funnel-shaped flower tubes for the butterflies to feed.

Growing Phlox for Pollinators

Phlox breeding has focused on habit and color, and little attention has been paid to the ecological value. As such, to learn more, Mt. Cuba Center added ecological focus to this phlox study. With the help of citizen scientists as well as a graduate student at the University of Delaware during the last two years of the trial, observations were noted as to the number of butterfly visits to each of the cultivars studied.

I then looked at the top five performers in both the horticultural and ecological categories. Of the top five, only two garden phlox remain on top for both horticulture and ecological values—‘Jeana’ and ‘Lavelle’. ’Jeana’ was the phlox visited most by butterflies by a wide margin of 539 visits versus only 117 visits to Lavelle’.

Garden phlox ‘Jeana’

Garden phlox ‘Jeana’ was discovered growing along the Harpeth River near Nashville, Tennessee, and named after its discoverer, Jeana Prewitt. Standing five feet tall, this lavender-colored beauty produces an impressive floral display from mid-July through early September, during the times when butterfly activity is at its highest.

Curious attempts to answer this question “why ‘Jeana’ started by examining the nectar produced by ‘Jeana’ and several other cultivars. There was no difference in nectar volume or sugar content. However, there was a difference in flower size, especially the narrowness and shallowness of the flower tube found in ‘Jeana’. Although still unproven, the idea is that ‘Jeana’ was preferable because it allows butterflies to quickly access the nectar of many flowers without moving as frequently. In any case, the number of butterfly visits was by far the largest for ‘Jeana’, and that is good enough for me.

Supporting butterflies is not as simple as planting a garden full of Phlox paniculata ‘Jeana’. While ‘Jeana’ is excellent at feeding adult butterflies, it is important to remember that all butterflies start out as an egg laid on its host plant—many of which require specific host plants to start their life cycle. Eastern and Spicebush swallowtails were some of the most frequent visitors to the phlox trial.

The Eastern Tiger Swallowtail needs American hornbeam, ash, birch elm, hawthorn maple, serviceberry, sweet bay, tulip tree, black cherry or willow. The Spicebush Swallowtail needs spicebush, common sassafras (Sassafras albidum), Sweet bay (Magnolia virginiana), or tulip tree (Liriodendron tulipifera) for its host plants.

The caterpillar stage of these butterflies feed on several species of native trees. It’s easy to support the entire lifecycle of these pollinators simply by including one of their host plants in your landscape.

You can download a copy of this phlox plant trial or other plant trials from the Mt. Cuba Center website at www.mtcubacenter.org/research/trial-garden/.

Helen Yoest is the executive director of Bee Better, an area non-profit 501(C)(3) designing and educating area homeowners about building better backyards for birds, bees, and butterflies.