Plants of a Phlox Together

It has been in my mind to talk about Phlox paniculata, or garden phlox, for some time. Prior to writing this, I thought P. paniculata was European in origin, but have since learned it is thought to be native to the eastern half of the country, occurring from New England/New York south to Georgia. There is some question as to how native to Indiana the species was in the past, nonetheless, it can be found growing wild, and it has escaped cultivation and naturalized beyond its original habitat.

The stunningly large, long-lived mop head bloom is the outstanding characteristic of this species across all cultivars. Its single greatest drawback for most gardeners is the powdery mildew that invariably comes to haunt the leaves each summer, tainting an otherwise great border plant. This can be somewhat mitigated with cultural controls such as increasing airflow around the leaf surface by thinning out the stems. Keeping the roots cool and moist with a layer of mulch also is helpful.

Mildew on phlox points to a larger point I want to make. The presence of mildew on phlox leaves is partly if not largely a design error that has broader application within the garden. Much of our gardening woes arise from the WAY we design, not what we design. I have written in the past about intentional plant communities as an approach to a flower bed design and management. The typical approach to a perennial or mixed perennial planting I learned in school is to plant perennials in masses while juxtaposing a single plant or smaller grouping of plants along the way to create balanced interest. The problem with this approach is this is not the habit of many species, nor is this the natural structure of ANY habitat. Nature does not plant isolated plants in a sea of mulch. Nature is just itching to fill in the gaps with weeds, those pesky opportunists. At least our cousins across the pond plant their border plants close together to fill the gaps. However, the problem even with this approach becomes apparent when we look at typical phlox problems. 

The more out of context you place a species, the more stressed it will be, and the more it will depend on you to care for it. Phlox paniculata does not grow naturally in huge sweeps, but rather, as individuals amongst a mass of other plants. Siting it correctly in the flower bed will alleviate some of the pressure on the plant as well as create fewer problems for the gardener. Phlox paniculata grows often along moist woodland edges, or in floodplains (hence the layer of helpful mulch). Break up the planting and send them to their own corners, and there will be even fewer problems. This same mistake occurs with other species also such as New England aster, Symphyotrichum novae-angliae

Topics such as how to design intentional plant communities to create pleasing, lower maintenance landscapes that sustain all sorts of life are coming soon in our fall offering of the Landscapes for Life class series.

When a garden problem arises such as pest or disease pressure, taking the time to first ask why is this present in the first place, and discovering what is out of balance in the landscape ecosystem will inform much in designing a future solution.

Josh Steffen, Horticulture and Facilities Manager

One thought on “Plants of a Phlox Together

  1. It showed up uninvited in one of our landscapes. It was not a design issue. I really like it, and do not mind that it has proliferated there. Powdery mildew has not been a problem yet. I have never seen mildew on it.

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