Making Wise Plant Choices, Part 3:  Cultivars & Hybrids, 2025

by Elaine Mills, Extension Master Gardener
Photos by Elaine Mills unless otherwise indicated

Climate-Conscious Gardening

Join Master Gardeners in the Arlington/Alexandria unit of Virginia Cooperative Extension in a series of monthly articles updated from their original posting in 2021 as we explore the topic of climate change and practical actions individuals can take in their home landscapes in response.

Changes to our climate are influencing the choices we make about the plants we grow in our gardens. As explained in parts 1 and 2 of “Making Wise Plant Choices,” native plants, especially those identified as “keystone” species, may be best suited to environmental conditions and provide critical support to wildlife. In this article, we explore how and why some categories of natives may fulfill these functions better than others.

An important consideration in selecting native plants is whether to purchase so-called “straight species,” the forms that are found naturally in the wild, or cultivars, plants that are selections of naturally occurring variations within the species or those that have been produced by horticulturists through selective breeding for certain ornamental traits. Species are designated by an italicized two-part Latin name, while cultivars are indicated by an additional name in single quotes. For example, Heuchera villosa is the scientific name for hairy alumroot, and Heuchera villosa ‘Autumn Bride’ is the name of a cultivar bred for its showy flowers. Using these Latin names is a way to make certain you are acquiring the plant you want, because multiple plants may be known by the same common name.

Hybrid plants are the result of cross-pollination between two species in the same genus. While this process can occur in nature between plants in proximity with the resulting seeds growing into a new type of plant, most hybrids are created by plant breeders with a desire to combine traits from both parents. These forms are ideally indicated by the use of an “x” in the scientific name. For example, the hybrid Baptisia x varicolor ‘Twilite’ displays intermediate characteristics between its parent plants, Baptisia australis (blue wild indigo) and Baptisia sphaerocarpa (yellow wild indigo).

An advantage of choosing straight species of natives is that these plants have evolved with the local fauna as part of the food web, and they will be recognized by wildlife as sources of nectar and pollen or food for the caterpillar stage of butterflies and moths. A second important benefit of species in this time of climate change is that they reproduce sexually through pollination of flowers and production of seed. This gives them the genetic variability to adapt over time to varying growing conditions. Some cultivars, such as Echinacea purpurea ‘White Swan’ are commercially produced by seed, and these maintain genetic variation between plants even though they may appear quite similar. Most cultivars and hybrids, however, do not reproduce true-to-seed and are propagated vegetatively through cloning (taking a cutting). The resulting new plants are all genetically identical and cannot contribute to biodiversity.

One reason gardeners may choose a cultivar of a native plant (sometimes referred to as a “nativar”) is to find a compact plant to fit in a small garden space. For example, ‘Henry’s Garnet’ and ‘Little Henry’ are shorter cultivars of Virginia Sweetspire (Itea virginica), measuring 4 to 5 feet and 2 to 4 feet respectively, as opposed to the mature height of 6 to 10 feet for the straight species.

In 2018, entomologist Dr. Doug Tallamy conducted research trials in conjunction with Emily Baisden, a fellow at the Mt. Cuba Center, looking at six common cultivar traits in native plants and their impact on insect use of those plants. This study showed that selecting a woody plant, such as a shrub, that is smaller in stature does not have a negative impact on its ability to support food webs. Modifications to leaf color, however, were found to have a detrimental effect on leaf-feeding insects. For example, when foliage color in a shrub was changed from green to purple, resulting from the substitution of anthocyanins for chlorophyll, the change in chemistry meant the plant was not palatable as a host plant to the caterpillar life stage of Lepidoptera.

Changes to flowers can be equally problematic as shown in studies described by Dr. Annie White in her 2016 PhD dissertation. In comparing Echinacea purpurea (purple coneflower) with three modified forms, she demonstrated that when shape, color, and bloom time of the flowers were modified, two cultivars and a hybrid did not provide the same pollinator support as the straight species. For example, when additional petals of ‘Pink Double Delight,’ were substituted for reproductive parts of the central cone of Echinacea purpurea, the flowers became sterile and no longer offered rewards of nectar and pollen.

Interestingly, in 14 direct comparisons of species and cultivars in Penn State Extension’s Bees, Bugs, and Blooms Pollinator Trial (2012-2014), species were preferred by pollinators only 50 percent of the time. For example, the ‘Bluebird’ cultivar, a naturally occurring form discovered in a Guildford, Connecticut garden, outperformed the species Symphyotrichum laeve (smooth aster). Master Gardeners conducting the trial concluded that “…it is not possible to generalize that the cultivar is better than or poorer than the species.”

Similarly, the two-year field experiment Annie White conducted at two sites in Vermont showed that while pollinators strongly preferred species in eight of 11 pairings with cultivars or hybrids, in three cases, the cultivar ranked as equal or preferred. In fact, the lavender-flowered ‘Lavendelturm’ cultivar of Veronicastrum virginicum (culver’s-root) was more than twice as attractive to insects (1,347 to 616 visits) as the white-flowered straight species. Her final determination was that cultivars need to be evaluated on an individual basis.

A helpful resource for plant selection is the series of reports created by the Mt. Cuba Center, a botanical garden in Delaware, whose mission is to inspire an appreciation for the beauty and value of native plants. These publications describe the results of plant trials conducted with the home gardener in mind to evaluate native plants and related cultivars.  Genera of plants studied thus far include Vernonia, Amsonia, Carex, Hydrangea, Echinacea, Helenium, Phlox for sun and shade, Monarda, Baptisia, Coreopsis, Heuchera, and Aster (now Symphyotrichum and Eurybia).

While earlier Mt. Cuba trials rated individual plants based only on ornamental qualities or disease resistance, their most recent reports have also taken pollinator visitation into account. For example, in the report on Phlox for sun, Phlox paniculata ‘Jeana,’ a cultivar discovered along the Harpeth River in Tennessee, received the highest possible 5-star rating for a favorable horticultural evaluation combined with its outstanding attraction for butterflies.

Cultivars of native plants have become very popular in the horticulture trade, and straight species may sometimes be difficult to find. A recorded presentation in our Master Gardener Virtual Classroom, “Native Plant Species and Cultivars” provides a detailed analysis of the four sets of trials mentioned above with photos for comparison purposes. An accompanying handout differentiates between cultivars that have been bred and those that were naturally occurring variants to aid gardeners in making informed decisions about their plant purchases.

For gardeners in the Washington metropolitan area seeking a wider choice of straight species with a few selected cultivars, we recommend referring to lists of native-only sellers and periodic plant sales compiled by the Plant NoVA Natives campaign. Gardeners in other states should consult lists of native nurseries provided by their respective native plant societies.

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Resources

• “Echinacea Isn’t Itself Anymore.” August 25, 2021. New York Times.
• “How effective are nativars? with Doug Tallamy.” Podcast, May 28,2018. A Way to Garden.com.
• “How Native Plant Cultivars Affect Pollinators.” Video, April 2017. Grow Native Massachusetts.
• Martin, Susan. “Native Species or Cultivars of Native Plants – Does It Matter?” July 2020, Vol. 6. No. 7. The Garden Shed Newsletter. Piedmont Master Gardeners.
• “Mt. Cuba Center Puts Nativars to the Test.” February 6, 2018. In Defense of Plants.
• Trial Garden Reports, Mt. Cuba Center.
• White, Annie. “From Nursery to Nature: Evaluating Herbaceous Flowering Plants Versus Native Cultivars for Pollinator Habitat Restoration.” 2016. PhD dissertation, University of Vermont.