Pollinator decline is a hot topic. Many groups are pushing pollinator-friendly practices to help stave off pollinator decline in general and honeybee colony collapse disorder in particular. Stories on pollinator decline even appear in general news articles. People who never otherwise give a thought to the environment, or where their food comes from, have heard of pollinator declines and colony collapse. A couple of widespread recommendations for pollinator-friendly gardening are: to plant species that are native to the area being gardened; and to not plant horticultural cultivars or hybrids. A cultivar is a cultivated variety, an individual plant selected for a unique trait. All cultivars have a name in single quotes, usually in English though not always: ‘David’ phlox has white flowers and good mildew resistance, ‘White Icicle’ red-flowering currant has white flowers, ‘Granny Smith’ apple has green skin, firm tart flesh and is good for cooking. You’ll also find that some garden plants are natural varieties, like a naturally-occurring red-flowered dogwood, Cornus florida var. rubrum; or a naturally occurring subspecies like climbing hydrangea Hydrangea anomala ssp. petiolaris . Sometimes the ‘var’ or ‘ssp.’ is left out; you can infer it from the presence of three Latin names in italics. But, most of the red and pink flowering dogwoods in the trade are cultivars, not the naturally occurring variety. If your garden plant has a X in the name that means it’s a hybrid though that could mean a cross between two named cultivars of the same species, or between two different species.

What are the reasons behind these recommendations? Let’s take a look at the first one, planting native species. The logic behind this one is that plants that are native to your area will be the best adapted ones and won’t need supplemental irrigation or fertilizing, or much care at all; that they won’t be invasive, and that they will provide the best food sources for native insects and other wildlife. Now anyone who’s made the mistake of planting Douglas aster or Canada goldenrod in their garden can attest that yes, native plants can be very invasive in the wrong spot. But that aside: how to find out what’s native in your area? If you live in any low-density area that still has lots of natural vegetation and unpaved areas, planting native species will be both easy and effective. You can look at what’s growing around you to get an idea of what is native to your area. But if you live in a highly urbanized area your task is much more complicated. All or most of the native vegetation is gone. You can do a little research and find plant lists of what used to grow there, and plant those, but that doesn’t mean that what’s on the list you found is actually what used to grow on your site, and what used to grow there won’t necessarily be the best adapted plants for your site anymore. The urban environment is radically changed physically from the natural habitat it replaced. Pavement and buildings create a completely different environment for plants and wildlife than unbuilt environments. The soil in urban areas has been stripped of topsoil and organic matter, and bulldozed and compacted to make suitable building sites. Pavement blocks air and water from what soil is left. Pavement and storm drains deflect rain from infiltrating the soil and channel it away, leaving the soil dry while creating flash flooding elsewhere. Buildings create artificial shade, much denser and with a different color spectrum than the shade that any tree creates; and reflect heat and sunlight like a cliff face would. This is the urban heat island effect you’ve heard of, where cities can be significantly warmer that the surrounding rural areas. As far as your plants can tell, highly-developed parts of Seattle might be more like Spokane as far as temperature, humidity, insolation, and soil moisture go. So while, for example, vine maple and evergreen huckleberry used to grow in places like Seattle, and still do in more natural parts of town, planting these forest understory, humus-loving plants in disturbed soils in parking lot islands or on south-facing walls is a totally unnatural environment for them and they don’t do well at all. In the highly disturbed and radically altered urban environment, plants that used to be native to the site are not necessarily going to be the best adapted plant choices. Which doesn’t mean you can’t plant natives in these situations, but you will have to rethink what natives will be adapted to the current conditions, and plant those.

So what are the reasons behind the second recommendation, to not plant cultivars or hybrids? Hybrid species, since they combine the traits of two different species, may not provide the wildlife benefits of either parent (though some do) so you’ll want to check on that. Hybrid cardinal flowers, Lobelia x speciosa are not good for pollinators. One parent is a bumblebee flower, the other a hummingbird flower; the hybrid serves neither. On the other hand, hybrids of Louisiana native irises, Iris fulva and I. brevicaulis, combined the best of both parents to produce lots of nectar on long-lasting flowers. I. fulva is a hummingbird flower, while bumblebees prefer the purple-flowered hybrids. All garden roses and rhododendrons are complex mixes of several species, yet all are attractive to bees so long as the flowers are not too double. One reason given for not planting cultivars is that cultivars are said to not produce nectar or pollen for pollinators or appropriate food for native herbivorous insects. This is taken as gospel by native plant enthusiasts, but it’s not really true where nectar and pollen are involved. Keep in mind when someone tells you that cultivars don’t produce pollen or nectar, that nearly all our agricultural crops are cultivars and yet they still produce the pollen and nectar necessary for pollination by honey bees. ‘Fuji’ apple, anyone? For herbivores like caterpillars, native plants are critical and cultivars and hybrids could be bad-see my article How to Support Your Local Caterpillars. But nectar-feeding butterflies are not nearly so fussy as their herbivorous caterpillars. Yes some cultivars don’t produce much nectar, but many do, and some even produce more nectar than their parent species (‘Jeana’ phlox is particularly good for butterflies)! And many cultivars are perfectly good food sources for the herbivorous insects that feed on their parent species. It is true that plant breeders don’t select for nectar production but it doesn’t mean that nectar production is automatically lost – just because a trait is not being selected for doesn’t mean it always disappears. We still have an appendix, after all. Finding information on which cultivars are still good wildlife plantings is not going to be easy though. What research is done on nectar production, is done on agricultural crops used by honey bees, so not terribly applicable to butterfly gardening. Also measuring nectar production is complicated. In many species nectar is produced on a cycle, not continuously; there will be peaks in production every 8 hours or 24 hours depending on species and cultivar. Nectar production also depends on weather and plant moisture status, and can vary with how many pollinator visits an individual flower has had. It’s more than just counting pollinator visits since you can’t tell how much nectar each visit produces and what the sugar balance is – yes, that varies too. A very little research is being done on garden plants for native pollinators, mostly at the Mt. Cuba Center in Delaware and by Annie White at the University of Vermont, by the count-the-visits methods, but that usually does not include butterflies. Even so we can see that results are all over the map and vary not just by specific cultivar, but by specific pollinator too.

A few generalizations have been established, which you can use to inform your decisions. Most important is that if you can’t see the flower’s stamens when it’s open, it’s no good as a pollen or nectar source. This rules out full, double flowers, like most garden roses and dahlias, and double-flowered petunias. This is not new information though, this has been well known for the many decades that I have been working in horticulture. ‘Double flower’ means the flower has extra rows of petals, sometimes replacing stamens. A single flower has a single row of petals; semi-double flowers have one or two extra rows of petals; double flowers have more than that. Another useful generalization is that if the flower color is significantly shifted from the parent species, then it probably won’t attract the same pollinators, although exceptions exist. Butterflies prefer flowers in reds, oranges, yellows, pinks and purples, but my white coneflowers attract more skippers than the natural purple color. For herbivorous insects like caterpillars, a good generalization is that blue, purple or red foliage color won’t be good. The chemicals the plant produces that make the leaves red or purple seem to be toxic to insect herbivores. These chemical pigments are always present in small amounts which leave the leaves green, but you can see a red tinge to the green leaves when the plant is stressed by cold or drought. Blue color comes from wax on the leaves-obviously not good.

Another reason given for not planting cultivars is that in most cases they are propagated vegetatively, so every plant is a clone of every other plant of the same cultivar. (There are many cultivars that are propagated from seed, like most vegetables, field crops and annual flowers but I can’t explain how that works, but obviously they’re not clones. ‘Cascadia’ snap pea, ‘Trailing Sapphire’ lobelia, ‘Walla Walla’ onion are examples.) This is said to reduce genetic diversity in the garden. This is very important in large scale ecological restoration projects but hardly matters at all in your city garden. Just how many plants of one cultivar were you planning on getting? Most people buy one or three of everything, not 100 of the same thing. So yes your rudbeckia might be the same cultivar as your neighbor’s down the block but there are plenty of other unrelated plants in between to provide diversity. Fortunately the rudbeckia cultivar ‘Goldsturm’, by far the most common in nurseries, is equally attractive to pollinators as its parent species. And the rudbeckias the new neighbor buys next year will be different from what you have – garden cultivars come and go out of fashion like every- thing else. Sure, when I’m buying hundreds of kinnikinnik plants for an ecological restoration project, I look for a restoration nursery that propagates from seed for genetic diversity, I don’t buy the garden cultivar ‘Vancouver Jade’ available at any local nursery. But if you’re buying a dozen plants for your garden, at that scale, the lack of diversity doesn’t matter all that much. Better to have a few cultivars of a native, than a nonnative species, for insect habitat.

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