The question of how many native plants, or native plant species, a garden should contain to be considered a native plant garden, comes up all the time. The question we should probably be asking ourselves is, “When does my garden become ecologically beneficial?”
If you really want to support the ecosystem, the prevailing wisdom is that your landscape/garden should contain at least 70 percent native plants (that’s biomass, not number of plants). The more native plants you have, the more likely you are to get to that tipping point, when your garden is going to support more wildlife, more insects, and become ecologically significant. There is some research backing up the 70 percent number.* A 2018 article in Smithsonian Magazine concluded that suburban yards with less than 70 percent native plant biomass could not sustain nesting Carolina chickadees. This research is east-coast centric, and while there is research going on in the west to see if numbers like these can be replicated here, we have yet to see results. If you really want to support the ecosystem, the prevailing wisdom is that your landscape/garden should contain at least 70 percent native plants (that’s biomass, not number of plants). The more native plants you have, the more likely you are to get to that tipping point, when your garden is going to support more wildlife, more insects, and become ecologically significant. There is some research backing up the 70 percent number.* A 2018 article in Smithsonian Magazine concluded that suburban yards with less than 70 percent native plant biomass could not sustain nesting Carolina chickadees. This research is east-coast centric, and while there is research going on in the west to see if numbers like these can be replicated here, we have yet to see results.
Wild Ones Front Range chapter (thank you, Jen Smith) came up with the following statement, which we feel really reflects our values:
“We support everyone who wants to add more native plants to their part of the Front Range, from a handful to a yard full. Each native plant that you add provides a landing place, food source, and/or a nesting site for local wildlife. The more native plants there are, the bigger the impact! If your goal is to create a sustainable biodiverse habitat, we suggest incorporating at least 70 percent native species into your landscape.”
What about nativars or cultivars? Do they have the same ecological value as the straight native species?
So, we first have to define some terms. These definitions come from the national Wild Ones’ website, unless otherwise noted.
A native plant species “is one that occurs naturally in a particular region, ecosystem and/or habitat, and was present prior to European settlement. These plants have held an ecological niche in our landscape for centuries and reproduce, primarily, through open pollination. These plants are sometimes referred to as straight-species or wild-type natives.” Doug Tallamy and Rick Darke, in their book, The Living Landscape, offer another definition: “a plant or animal that has evolved in a given place over a period of time sufficient to develop complex and essential relationships with the physical environment and other organisms in a given ecological community.”
A cultivar is “any plant that is developed or selected for its desirable characteristics and maintained by propagation. Cultivars are reproduced through cloning methods such as grafting, cutting, root divisions, layering, tissue culture, etc.”**
Pawnee Buttes Sand Cherry — this nativar is a low-growing, creeping form of the native Western Sand Cherry shrub (Prunus besseyi). Photo courtesy of Conservation Garden Park.
A nativar is “a cultivar that came from a straight-species native plant. Nativars are propagated for many reasons: flower colors or forms, compact size, insect or disease resistance, tolerance of certain environmental conditions, and more. Nativars can be a native plant that is a genetic variant found in nature that is then selected and propagated to retain a particular or unique aspect. They can also be obtained through the process of artificial selection in which plant breeders grow plants with desirable characteristics and eliminate those with less desirable characteristics.”
Wild Ones National has a policy to answer the question whether nativars have the same ecological value as straight-species plants. The short answer is we need more research, but probably no. Here are some highlights of the policy, and some information, below, is taken verbatum from the policy:
“Wild Ones advocates for selecting native plants and seeds originating from local or regional sources, having similar environmental conditions as the planting site [environmental conditions include soil characteristics, drainage, pH, sun/shade, prevailing wind direction, temperature range, precipitation, elevation, aspect/slope]. Such planting material is often referred to as the “local genotype.” Why?
To preserve the genetic diversity and integrity of native plants. Whether in landscaped or natural areas, an all-important concern is preserving not only a diversity of plant species, but also the genetic diversity within each species. Native plants grown from seed carry the wealth of their native gene pool. They perpetuate this diversity as they grow and participate in successful pollination. This genetic diversity helps whole species to survive and adapt when confronted by environmental stress. Each successive generation of plants reproducing in this manner continues to maintain a rich heritage. Native species vary genetically in their adaptation to their environmental conditions and ecological relationships where they grow. This results in various genotypes for the same species over its range. If only a small percentage of the plants being planted in gardens and landscapes are nativars there would be no concern. However, the mass-production and increased use of nativars over straight species native plants is a concern for ecologists, environmentally friendly gardeners, horticulturists, and native plant professionals. Straight species open-pollinated plants, and the genetic diversity they contain, are the foundation of both nature and horticulture. They are the building blocks of future horticultural selections as well as the key to ecological preservation.
To help support other species. Pollinators, other insects, birds, mammals, and other wildlife have co-evolved with local genotype plants and depend upon them for seasonally-available food and shelter in a well-functioning habitat. Annie White, at the University of Vermont, in her dissertation, From Nursery to Nature: Evaluating Native Herbaceous Flowering Plants Versus Native Cultivars for Pollinator Habitat Restoration (2018), found that when particular nativars varied significantly in color, size, or shape from their wild-type, they provided less ecological service to pollinators. Additional work by White includes, “How Native Plant Cultivars Affect Pollinators” (2020). Her research recognized that ‘native wild vs. native cultivar’ studies need to be conducted to better understand how different cultivar species may or may not be an equal replacement for their native type. More research is needed on this topic.
To ensure the greatest success in your landscaping efforts. Take your cues from nature. The more closely you match your environmental conditions with the plant species’ naturally-occurring habitat, the better your native plants will thrive. Complex interactions develop between species within habitats, so also consider growing a few more plants associated from the same habitat for optimal growth.
How do you know if you have a nativar or a straight species plant?
Nativars can be identified by checking for a variety name, in addition to the species name, which is given on a tag or catalog. For example, Brandywine red maple, Acer rubrum ‘Brandywine’, is a cultivar, whereas the native, from which it is derived, would simply be labeled as Red Maple, Acer rubrum.
Request native plants when you buy
The safest policy right now is to encourage the use of straight species. Ask for them at your local nursery; encourage nursery management to start stocking more straight species. The nursery industry has not embraced the message that native plants are more about ecosystem function than about looks. We have to convince them that there is a market for plants with high function.
While a nativar will most likely be a better ecological fit for North American gardens than an exotic species from Asia or Europe, it remains to be seen to what extent it can fill the ecological niche and provide the genetic richness of a native plant. There is a lot we still don’t know, and it seems reasonable to stick to straight species native plants, if you can. But, again, we could use more research!
Footnotes:
* In a study by D.L Narango, D.W. Tallamy, and P.P. Marra, Nonnative Plants Reduce Population Growth of an Insectivorous Bird, 2018, found that chickadees foraged 86 percent of the time on native plants. Chickadees achieved successful replication rates ONLY in yards with less than 30 percent introduced woody plants. This study, and others, underlines the importance of landscapes with at least 70 percent native plants for optimal ecological stability. Again, these percentages relate to biomass, not number of plants.
** A cultivar is bred for many different reasons. It can be bred to have different colors or blooms. These changes can be detrimental to insects or insect larvae. Plants bred for double flowers, for example, can be devoid of pollen or nectar, and useless to insects. And a change in color might alter markings that a pollinator needed to identify the flower or leaves.
