Choosing between cultivars

Despite my recent interest in planting straight native plants, I’ve got lots of cultivars in my garden and expect to bring home more in future. Cultivars are improved versions of a species, selected or bred for desirable characteristics such as bigger flowers or new flower colors. Cultivars of native species are sometimes called “nativars.”

This coneflower, Echinacea 'Sundown', is a nativar-photo Mike Peel

    I’m used to thinking that cultivars are selections culled from nursery beds or native plant populations by sharp-eyed growers. But this is only one of the paths to a market-worthy cultivar, I’ve learned. Other cultivars are the products of intentional breeding programs. Once they’ve been found or developed, cultivars will be propagated asexually, through cuttings or divisions, so that the offspring will be exactly like the parent. That means they won’t add genetic diversity to your landscape, as native species will.

    At a recent garden club meeting, a member asked me whether her white-flowered coneflower cultivar counts as a native for the purpose of attracting desirable insects. It’s an important question and an area of active research. Recording native pollinator visits to flowering phlox plants, both straight natives and cultivars, Keith Nevison, a researcher at Mt. Cuba Center in Delaware, was surprised to find that a cultivar, Phlox paniculata ‘Jeana’, attracted the most pollinators. He hypothesized that this might be because ‘Jeana’ blooms so generously and has small, shallow flowers that are easy for pollinators to use.

Tiger swallowtail on Phlox 'Jeana'-photo Michele Dorsey Walfred

    Similarly, the Nativars Research Project of the Chicago Botanic Garden used citizen scientist observations through project Budburst to determine that cultivars vary widely in their attractiveness to pollinators. Among beardtongues (Penstemon digitalis), for example, popular cultivars ‘Husker Red’ and ‘Blackbeard’, loved for their deep purple foliage, drew far fewer insects than ‘Pocahontas’. 

Penstemon 'Pocahontas' at Bluestone Perennials

Scientists suggest that the difference is in the origin of the plants. ‘Pocahontas’ was discovered in the wild. That’s something it has in common with Phlox ‘Jeana’, which was found growing wild outside Nashville. Apparently when plants change in the wild, the new genetic mixes that survive are the ones that cooperate successfully with local insects.

    Some early guidelines seem to be developing for gardeners who want to pick plants to benefit pollinators. Cultivar flowers that resemble the native’s most closely are more likely to attract insects than blooms that have been radically altered in the breeding process.

Echinacea 'Razzmatazz' is probably too different from its straight native ancestor

And now we can surmise that wild-selected cultivars are also more likely to be popular with pollinators than cultivars produced by human breeding efforts. Much more research will be needed before we can be sure which cultivars to plant for pollinators.

    So what about that white-flowered coneflower? Where did it come from? I see that Echinacea ‘White Swan’ may have been introduced by Piet Oudolf, the legendary Dutch garden designer. Did he find it growing in his garden? I can’t tell.

Piet Oudolf border, Royal Horticultural Society Garden Wisley, with white coneflower bottom right-photo Esther Westerveld

    Growers introduce lots of new cultivars of native plants every year. Right now, I think the only way we can determine which ones are most popular with pollinators is to plant them and observe.