Tuesday, April 16, 2024

Native Plants vs. “Nativar” Plants: Do Pollinators Notice a Difference?

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Native plants are all the rage these days, and for good reason: They support regional wildlife, are adapted to the local climate, and require minimal maintenance. But they don’t always fit perfectly into a vegetable garden. Although many wild plants are perfectly suited to cultivation, natives are sometimes lanky, making them difficult to fit into the average small plot.

Enter cultivars of native species – or “nativars” (an unscientific term defined as a deliberately bred, crossed or hybridized variation of a native species), the plant industry’s attempt to improve nature. Given an aster with abundant amounts of sparkling blue flowers in the fall, for example, they will imagine that the packaging would look better in pink. It’s not just about aesthetic changes; breeders also focus on creating plants that are more resistant to disease. But are these varieties just as attractive to the insects and birds that depend on them for their livelihood? Researchers worked to find the answer.

In 2011, Annie White was about to start Nectar Landscape Design Studio when she hit a roadblock trying to find some native species at local nurseries. To find out if nativar substitutes would be just as effective from a pollinator perspective, she embarked on a doctoral research program. Working with the University of Vermont, White began a field study in two Vermont locations, collecting data through 2015. She planted 11 paired native species side-by-side with one cultivar, then observed about 8 000 visits from several groups of pollinators, including bumblebees, honeybees, small dusky bees, beetles/insects, butterflies/moths, flies and wasps/ants.

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His discoveries? “Half the time there was a preference for native species, and half the time there was no significant difference. » Only ‘Lavender Towers’, a cultivar of Culver’s root (Veronicastrum virginicum), surpassed the species in terms of pollinator visits. On the other hand, certain cultivars have been noticeably snubbed by pollinators. The pink-flowered aster ‘Alma Potschke’ bombed. Tradescantia “Red Grape” also received a negative review.

What drove pollinator preferences? White suspected that nectar quantities might play a major role. Flower color and flowering time could also be factors.

Other researchers are also looking for answers. The Mt. Cuba Center in Hockessin, Del., has a test garden (open to the public) conducting comparison tests of species native to the eastern United States and their cultivars. Their studies mainly focus on the value of the garden. But thanks to the local Pollinator Monitoring Team, a group of 10 to 20 trained volunteers, recent trials are also collecting data on what pollinators do. They confirmed that pollinators prefer natives with which they have co-evolved. “Species are always the benchmark,” says Sam Hoadley, head of horticultural research at the center.

In some cases, however, pollinators have turned to cultivars. A try with Beebalm (monarda) found that the bright red flowering nativar Monarda didyme, “Jacob Cline” outdid the species in hummingbird visits, 273 to 22. Meanwhile, the pale purple nativar Fistulous monarda, ‘Claire Grace’ also outperformed the species in terms of moth and butterfly visits. Another notable Nativar surprise was Phlox paniculate, “Jeana,” which outperformed the species “by far,” Hoadley says.

Flowering time can impact pollinator preferences. Although most native species overlap, this is not always the case. Some have a completely different flowering window. Hoadley also says management issues, such as pruning, can throw any plant out of sync with its pollinators. “Delayed flowering can make them inaccessible, especially to specialized insects,” he explains. And specialized insects that rely on a plant species for survival tend to pay the price when things get out of sync. “There are many things to consider,” says Hoadley.

Graduate research assistant Jen Hayes conducted a similar study at Oregon State University. She planted seven native species alongside their corresponding cultivars and observed the reactions of bees, butterflies and hoverflies for three years. The data is still being analyzed, but Hayes’ findings are similar to other studies: pollinators generally prefer native species, and these plants also attract more specialized bees and more diverse pollinators.

All the studies also confirmed what gardeners have long suspected: the closer a nativar is to the original species, the greater the appeal. Significantly altered flowers, including double coneflowers (“Pink Double Delight” in White’s study, for example) with petals in place of reproductive parts, only confuse pollinators.

In contrast, changes in a plant’s size and leaf color do not appear to affect pollinator interest, according to studies at Mount Cuba. Varieties with chartreuse or variegated leaves, or more compact plants, generally perform as well as the native plant, although caterpillar activity on red and purple leafed shrub cultivars is still being studied.

The Nativars have generally performed relatively well, but there is also the future to consider. If we want to keep plants and corresponding insect populations healthy and thriving, genetic diversity must inform our choices. A native species has the greatest genetic diversity to create offspring that will survive stress, especially in the face of the challenges of climate change. When gardeners shop locally and look for nurseries that collect seeds from plants native to the nearby area, the resulting plants will have the trait set suited to local conditions. Natives, with less genetic diversity, do not have this advantage. For example, in White’s studies in Vermont, several nativars failed to survive harsh winters.

However, we should not dismiss nativars entirely; they occupy a niche. They provide a sort of introduction to the native world for gardeners, especially those in urban areas or small spaces who want to make an environmental impact in less than ideal growing conditions. This is especially true for plants (such as coneflowers) that are readily available at local nurseries.

No one should feel like they have to be a purist, Hoadley says. “Often, nativars inspire people to get started with using native plants, bringing them into the conversation while believing they are doing something right.”

Tovah Martin is a freelance gardener and writer in Connecticut. Find it online at tovahmartin.com.

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