Why You Should Plant Native Plants Instead Of Cultivars

When starting your Native Plant journey into gardening there is much to learn. So much so that it can be confusing with the different terminology of the plants like natives, ecotypes, cultivars, hybrids….it can get overwhelming. In this article I’m going to clear up any confusion you may have as to the difference between natives & cultivars. And I will show you why it is almost always better to plant straight native species for wildlife.

Although I’ve written a detailed article on the difference between natives, varieties and cultivars before, I felt that I should revisit the topic but with a greater focus on the reasons why straight native species are almost always better for local wildlife and pollinators. I will go over several reasons why modifying physical characteristics of plants can result in reduced pollinator visits, and summarize the results of peer reviewed research on this topic. My goal is to arm you with enough information to successfully select your native plants to complete your gardening goals, while maximizing the benefits for your local ecosystem.

In short, nature is a complex system filled with complex relationships & interactions between plants and pollinators that took millennia to evolve. When we begin modifying physical characteristics or morphology of flowers, we risk alternating this relationship. And research has shown that often this results in plants less attractive to pollinators.

In this article

• What is the difference between a Native and Cultivar
• Why cultivars may not be as attractive to pollinators
  • Potential effects of changing flower or leaf color
  • How nectar can be effected
  • Physical differences and pollinator effectiveness
  • Harming the local plant gene pool
• Research into pollinator visits – comparing natives and cultivars
• Conclusion

What is the difference between a Native and Cultivar

When comparing native flowers available for a garden, at some point you will undoubtedly be faced with a choice between a straight native species versus a cultivar. If gardening for wildlife is your primary goal, then as a general rule you should choose straight native species, as they will almost always be better for pollinators.

• Native , or ‘straight-native’ refers to the straight species as it is found in the wild, and is endemic to your local region since before European settlers arrived. [1]
• Selected variety refers to a native species that was ‘selected’ for a certain characteristic, and whose seed will produce more of that same characteristic. Common examples include natural white Echinacea or White Redbud trees.
• Cultivar can refer to any native that has one or more traits that is genetically different from the native, and is often ‘cultivated’ by growers via hybridization or cuttings. These differences are often reflected in the size, color, or bloom time, but can extend to many other characteristics.

Should you use cultivars or straight natives?

When evaluating what plants you wish to grow in your pollinator garden, as a general rule, you should use straight native species. In some cases cultivars can be as attractive as natives, but each species or cultivar requires it’s own evaluation.

I have summarized some research into this topic at the end of the article that I encourage you to review. As well as offer some further resources for researching specific cultivars that has been conducted. [jump to research]

Why cultivars may not be as attractive to pollinators

Cultivars are genetically different than natives and are created for a specific trait such as size or color. Cultivars either the result of natural selection, hybridization, or propagated vegetatively through cuttings. These genetic changes can extend to nectar, pollen, or their replenishment – often making the plant less attractive to pollinators.

Pollinators such as bees have evolved to associate certain physical traits with a nectar or pollen reward. [2] These traits include flower color, shape, size, nectar aroma, and nectar replenishment. As a general rule you can state that straight native species will always be attractive to pollinators, as they have coevolved over millennia.

Based on all the papers I read in researching this topic, cultivars are less attractive than straight native species most of the time. Naturally occurring, selected varieties often performed just as well as their straight-native cousins, and in rare cases perform better such as Fall Phlox ‘jenna’ or Veronicastrum virginicum ‘Lavendelturm’. [3][4] In virtually all cases I have reviewed, hybridized or vegetatively propagated cultivars were less attractive to pollinators.

Effects of changing flower color

Pollinators use color to help guide them to the nectar/pollen of flowers. For instance bees see color in a different light spectrum than humans.[5] A bee can see a different light spectrum than humans, and are most sensitive to UV light (which we cannot see). [6][7] Furthermore, bees cannot see the color red. So, the bright red flowers may not be visited very often, unless the aroma or some invisible UV light is attracting them.

How nectar can be effected by cultivars

While the nectar of a flower is mostly sugar and water, there are other chemicals and compounds that give it a unique aroma [8]. Pollen also has a unique aroma that alone can attract certain and specialized species.[9] Changes to pollen and nectar in cultivars are a risk.

Unless the compounds in the cultivar nectar and pollen are studied, there is a risk that their chemical make-up could be altered. And while it is theoretically possible that modifications to nectar and pollen could improve attractiveness, I am unaware of any research that has born this out. In fact, most research shows that cultivars, particularly those from hybrids or vegetative propagation are less-attractive to pollinators. [3]

Nectar replenishment / reservoir

The amount of nectar held by a flower is known as standing crop, and the rate that this amount is replenished is known as the secretion rate. So a flower with a larger standing crop, or higher secretion rate would most likely be more attractive to pollinators. This is an important point, as when we breed flowers for different forms than the straight native, we risk effecting both the size of the standing crop and the rate of replenishment. [10]

Research around the world has shown that modifications to straight natives can affect the amount of nectar/pollen, and their replenishment. A study in the UK found that double blooms of certain species yielded almost no nectar, while other studies at the Mount Cuba Center have found most Echinacea cultivars to be inferior to straight natives, which matches research from Dr. Annie White from the University of Vermont. [3][11][12]

Physical changes can prevent pollination

In addition modifying color, nectar aroma or replenishment, some cultivars are bred for their physical unique form. These modified physical characteristics can have unintended consequences such as preventing pollination or reducing corolla diameters that make the flowers less attractive. [3][13]

How cultivars can potentially harm the local gene pool

Any cultivar that can reproduce itself can carry a risk to modifying local genetics. This is more true in plants that cannot self-pollinate. However if cultivars can intermix with local genetics, it is possible that they cause genetic drift or replace local ecotype, potentially causing wider harm. [14]

While at first glance this may seem ok, as in the cultivar seems to be doing better than the straight native species, this condition may not last. We must remember – nature is complicated. And there are documented instances where a cultivar may grow faster than natives, but perhaps is less resistant to disease or harsh climate conditions that may be rare, but will occur again.

Disease resistance

This occurred in California in the 70’s when Douglas Fir trees from the coast were planted inland, and grew faster than their local cousins. However, they were not resistant to certain diseases (which were initially dormant). But when the disease reappeared, it wiped out large tracts of coastal Douglas Firs. [15]

Climate resistance

I have to return to Dr. White’s work again. In her research she found that many different cultivars, even the natural selected varieties often had trouble surviving the harsher Winter of Vermont. You see, many of the species she studied (and their cultivars) were nominally rated as hardy to her zone. But she often found that the cultivars had a lower Winter survival rate in zone 4. [3] It is not hard to imagine a scenario where a cultivar is used in restoration and does well…..until an exceptionally cold Winter or hot Summer occurs.

Research into Natives vs Cultivars – what the Science says

In researching this article I found multiple studies that did evaluate pollinator attractiveness by comparing visits to straight natives versus cultivars, as well as other studies that examined pollinator attractiveness to various cultivars examining their physical features, etc.

Research of Dr. White, University of Vermont

Dr. White of the University of Vermont published a comprehensive thesis examining 11 species of natives and cultivars and how frequently they were visited by pollinators. In her work she also compared the straight native Echinacea purpurea to several of it’s hybrids.

The results of her research show that in the vast majority of cases, hybridized or non-natural cultivars were less attractive to pollinators than straight natives, or naturally selected varieties (natural mutations). In comparing the natural mutations to the straight natives, she found that the performance was generally statistically the same with the exception of Echinacea purpurea vs Echinacea White Swan, in which the straight native was better in regards to bees. And when comparing Culver’s Root, she found the selected variety ‘Lavendelturm’ outperformed the straight native species.

Mount Cuba Center

The Mount Cuba Center located in Delaware is a public garden that conducts much research in comparing cultivars to straight natives for pollinator visits. Their website has much available for evaluating cultivars versus natives. You need to read their ratings carefully though, as they sometimes evaluate more than just pollinator visits. They often include disease resistance, foliage appearance, or overall plant aesthetics.

In researching their resources, I did come across a large number of cultivars that can outperform the straight natives per their research. Some examples are Fall Phlox ‘Jenna’ [4], Hydrangea arborescens ‘Dardom’, and Monarda fistulosa ‘claire grace’.

Click Here for Mount Cuba Center & Research on cultivars.

Examining physical characteristics

Other research has been done on examining physical characteristics of selected or hybridized varieties for UK native plants and various Blueberry bushes. In the UK they found nectar differences in various plants such as Birdsfoot Trefoil where double bloomed varieties produced little to no nectar.

For blueberry bushes, the researchers noted that there appeared to be a direct relationship between pollinator preference and corolla size. This seems logical as a smaller diameter corolla would be more difficult for a bee to reach the nectar. [13]

Conclusion

When comparing cultivars and straight native species, we can say that the straight native species will always be beneficial and not be harmful, 100% of the time. However, there are some documented cases where varieties outperform straight species in pollinator visits. But as a general rule, the straight native performs as well or better than cultivators.

If one is interested in planting varieties, or cultivars, know that each species will require careful research to determine if it is as good, better, or worse than the straight species. And as we have seen in the published research and surveys, cultivars are generally not as attractive to pollinators as their straight species counterparts.

We humans often approach problems examining single variables, as it is more simple to understand and study. But in complex systems such as nature, we may frequently introduce second order effects or make other minute changes to a plants physical characteristics that can have a negative effect on the plant/pollinator relationship.

Greenhouses and nurseries often choose selected varieties or make hybrids based on the physical looks or appeal of a flower. In other cases they choose cultivars based on size or resistance to a disease such as powdery mildew. But the most important factor they use in choosing what cultivar to pollinate is aesthetic appeal. This makes sense, as unique attractive flowers will sell.

As noted in Dr. White’s paper, we have the knowhow to try to maximize pollinator attractiveness in selecting & breeding of cultivars, and it is possible that the nursery industry will see a market opportunity in the future. As pollinator and native plant gardens increase in popularity, some entrepreneur may find a niche market for various cultivars that drive further development. As of now, that doesn’t seem to be the case, but time will tell.

Nonetheless, if you wish to maximize wildlife in your garden, it is still a safe choice to choose straight native species. The complex relationships that have evolved over time are still there, and you will be rewarded by pollinators by designing your gardens based on native plants.

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