Making Wise Plant Choices, Part 3:  Cultivars

Climate-Conscious Gardening

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

Mt. Cuba Coreopsis Report
Photo courtesy of Mt. Cuba

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

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 have been produced by horticulturists through selective breeding for certain ornamental traits or were selections of naturally occurring variations within the species. 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.

Straight species of hairy alumroot - green leaves with foamy white flowers
Straight species of Heuchera villosa (hairy alumroot).
Photo © Elaine Mills
The ‘Autumn Bride’ variety of hair alumroot has especially showy flowers.
Heuchera villosa ‘Autumn Bride’ has especially showy flowers.
Photo © Elaine Mills

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. Cultivars, on the other hand, often do not produce true-to-seed. They are usually propagated vegetatively through cloning (taking a cutting), and the resulting new plants are all genetically identical and cannot contribute to biodiversity. Some cultivars are commercially produced by seed, however, and these have genetic variation between plants even though they may appear quite similar.

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 3 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 as palatable as a host plant to the caterpillar life stage of Lepidoptera.

Leaves of the straight species of Arrowwood Viburnum with green leaves
Green leaves of the straight species of Viburnum dendatum (arrowwood viburnum).Photo © Elaine Mills
‘Red Feather’ cultivar of Arrowwood Viburnum with modified foliage
‘Red Feather’ cultivar ofViburnum dendatum (arrowwood viburnum) with modified foliage.Photo © Elaine Mills

Changes to flowers can be equally problematic as shown in studies by Dr. Annie White. Over two years, she compared flower visitation by insect pollinators to 12 native herbaceous plant species and 14 native cultivars in a field experiment at two sites. While some of the cultivars in the study were equally attractive to insects, the flowers in which shape, color, and bloom time were modified, did not provide comparable support. For example, when additional petals were substituted for reproductive parts of the central cone of Purple Coneflower, as in the double-flowered ‘Pink Double Delight,’ the flowers became sterile and no longer offered rewards of nectar and pollen.

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 for both their aesthetic qualities and ecological value to wildlife.  Genera of plants studied thus far include Echinacea, Helenium, Phlox for sun and shade, Monarda, Baptisia, Coreopsis, Heuchera, and Asters. Individual plants receive a rating based on such factors as hardiness, disease resistance, floral display, foliage quality, and pollinator visitation.

Cultivars of native plants have become very popular in the horticulture trade, and straight species may sometimes be difficult to find. For gardeners 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.



Resources

This entry was posted in Climate Change, Native Plants. Bookmark the permalink.