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What's a Cultivar? Why Should You Care?

Now is the time of year when gardeners start getting anxious to plan what new and interesting things they can add to their gardens this year. Most head straight to the garden center on the first warm weekend and pick up whatever they see that is blooming and pretty that day. If you're planting for pollinators, you may notice plenty of marketing materials on displays and plant tags letting you know that these plants are good for your pollinator garden. But that's not always necessarily true.

To be truly useful to the pollinators in your region, the plant needs to also be from your region. Native. Locally native. Many "pollinator plants" in stores and those pre-planned pollinator gardens you can order online are not the right plants to best serve the pollinators in your neighborhood. In fact, many of them are what we call exotic - not even native to North America. The classic example is the butterfly bush (Buddleia) -- great marketing program, very poor ecological value. It's also invasive. Did you know that insects need the right balance of carbs, protein, and fats just like humans do? Exotic plants do not provide the right balance of nutrients. Providing a butterfly bush for your butterflies is like raising a toddler on soda. And no native butterflies can lay their eggs or make new butterflies on a butterfly bush.

Making it more confusing, the plant market is crammed full of native plant cultivars, sometimes called "nativars". Dozens of new nativars hit the market every year, but even if you know that a plant is locally native to you, the cultivar version may not be useful to insects.

If you've been following me for a while, you know that native plants and native insects and other wildlife have evolved together and have beneficial relationships with each other. Some insects are specialists and can only use 1 or 2 plants for food. Some are generalists and can eat a wide array of plants. But when a plant is altered by growers, the traits that make it right for wildlife may change.

I'll explain in a moment. But first, let's take a look at some plant tags. First up is Asclepias tuberosa, butterfly weed - classic host plant for monarch butterflies, a specialist insect.

On the left is the tag of a straight species plant. It's labeled "Mid-Atlantic Native". Yay! We know it's useful to us here in the Mid-Atlantic! On the right is the cultivar called 'Hello Yellow'. The picture shows us it's a different color. A nice color, especially if you're like me and have a aversion to orange.

Let's flip the tags over and read further. Now we can see that 'Hello Yellow' is expected to stay a full foot shorter than the straight species. The remaining characteristics are the same (as far as we can tell). Two changes we know of: color and size. Do the monarchs care? Monarchs use this plant as food for caterpillars, and we're going to guess that nothing has changed about the leaves that would make it unusable for that. But the flower color is different, so maybe that will affect how easily the plant is identified by a monarch butterfly as a good place to lay her eggs. Maybe it's not a problem. I don't know if anyone is studying that.

Next let's take a look at Symphyotrichum oblongifolium, aromatic aster. The two cultivars we are looking at are 'Raydon's Favorite' and 'October Skies', both very commonly available in garden centers. Sometimes plant names change as scientists learn more about them and recategorize them. The plant labels of these two cultivars carry the outdated name of Aster oblongifolius. Change is hard.

You can see on the pictures that the color is slightly different from one to the other. Let's flip those over and see what else we can learn. The straight species and 'October Skies' were both similar in color, and are similar in size as well, although 'October Skies' blooms a little later into fall. 'Raydon's Favorite' blooms about the same time as the straight species, but in a slightly darker color and grows to a larger size. It also looks like you can grow this in one growing zone colder than 'October Skies.' That's about all we can tell about what has been altered about this plant. If you want to get a longer aster bloom time, plant both!

So, how does a cultivar come to exist in the first place? Here are some ways:

  • Naturally occurring plant communities have genetic variation. That means they have a range of tolerance to disease and herbivory (a fancy way to say how tasty they are to wildlife), sizes, flower colors, etc. Sometimes you find one that's a little bit different from the others, and that plant is selected for a potentially marketable new plant. The seeds of that plant will likely produce plants more similar to the wider community it came from than this particular individual, but once in a while they grow true from seed (in which they can be a rare seed-grown cultivar).

  • Intentional plant breeding by growers is not something I know a lot about, but generally plants are manipulated for certain traits. To be mass-marketable, a plant needs a tidy and generally more compact habit, sturdy stems, and a wonderful new flower color or form that hasn't been seen before. Patentable. Shippable.

Most plants grown for mass production and sold in garden centers are produced clonally - that means they are grown from cuttings or tissue culture and are all clones of each other. Zero genetic diversity. But that's only one problem. Here are some characteristics that may be altered and why it may be problematic:

  • Flower color: Perennials are usually "enhanced" by their flower color, which is purely to appeal to humans in the store. The problem is that insects seek out the plant they need by the color and markings of the flowers (and sometimes scent). They don't see the same wavelength of light that we do. They rely on colors and markings that are invisible to humans to find the right plant and point them to the pollen/nectar. The classic example is the coneflower, Echinacea purpurea. There are so many cultivars on the market who could possibly keep count. Why? They're easy to manipulate. Easy to sell. A classic, recognizable native plant in a brand-new color you don't have. Yet.

  • Flower form: Flowers can be manipulated to have different forms. An example of this takes us back to the coneflower. Many of them are changed from the classic "daisy" shape, to what I call a "pom". You can see them in the photo above (cream flowers). This new shape makes any nectar or pollen completely impossible for insects to reach and the flower becomes useless. It can't even produce seeds. Not a "pollinator plant" at all.

  • Bloom time: Perhaps not intentionally altered, but sometimes the bloom time and length of bloom are changed like in our aster above. This matters because most insects are active when their partner plants are blooming. If the plant is done blooming before they're ready to eat, it's once again rendered useless.

  • Size: This applies to perennials, but also to trees and shrubs. Smaller landscapes need smaller plants, right? Right? Many plants are manipulated to be more compact. This is generally not much of an issue, but we don't know what other traits may have also been changed unintentionally.

  • Foliage color: People seem to like variations on the theme of green. Some foliage has a blue or yellow tint to it, some are outright red, purple, or black. Some are multicolor or variegated with white. Initial research says that the biggest problem comes along with red/purple variations, as the chemical required to make these colors makes leaves unpalatable to insects. These may even be marketed as "pest resistant" because nothing will try to eat them. But if it's a native plant, we want our insects to eat them.

How do we know what traits matter to insects? Research. Penn State is doing some great research on pollinators. We are also fortunate here in the Mid-Atlantic to have Mt. Cuba Center's research. They study how well cultivars perform, both as people-pleasing garden plants and as a valuable ecological resource. You can find their trial garden research reports here: Mt. Cuba Center | Trial Garden

After all I've said above, now it's time to give cultivars some credit. Not all of them are less valuable to wildlife than their straight species parents. Some are just about the same. Some are actually better! Case in point: the garden phlox cultivar 'Jeana' got a 5 star ranking in Mt. Cuba Center's trials, had excellent powdery mildew resistance, and outperformed other cultivars in a huge way when it came to attracting butterflies. Similarly, the white coneflower (Echinacea purpurea) cultivar 'Fragrant Angel' attracted the most pollinators in the Echinacea trial, even more than the straight species. An excellent replacement for your daisies.

So what exactly do you buy? Let's go by these general guidelines:

  • Whenever possible, look for straight species, locally grown, local ecotype plants as these will have the most ecological value for your local wildlife. You can find these at your smaller local native specialty nurseries.

  • Look for plants you know are native at least to the Eastern US, if not specifically the Mid-Atlantic. There are a ton of options.

  • Decide what you want before you go and understand that not every plant is available when you want it. Plants are generally available for sale when they look their best, i.e. when they're blooming.

  • Avoid cultivars that have altered flower shapes or red/purple foliage.

  • Do not shop at big box stores. I mean it.

  • Nerd out and enjoy reading the research available at Mt. Cuba Center.

  • Ask your garden center if the plants have been treated with pesticides before or after arriving at their location. Unfortunately, many of these native plants have been treated with systemic pesticides at the grower, which may kill insects that try to eat them for perhaps (we're guessing here) a year after they're planted in the ground. Look for "Neonic Free" on the plant tag.

So what do you think? Do we need any more coneflower cultivars? Mt. Cuba's Echinacea trial started in 2018 and tested over 80 different Echinacea. I can't imagine how many more have been developed and released in the last 7 years. New and novel sells. Maybe proven ecological value should be a promotable feature as well.

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