Plants for Pollinators

Excerpt from an article of the same title by Gail Langellotto, Ph.D., assistant professor of horticulture, OSU, in the May issue of Digger, a monthly nursery industry publication published by the Oregon Association of Nurseries. Edited for brevity.

 
[Editor’s note: Planning a shade garden comes much more easily to me than trying to pull together a cohesive sunny garden. This isn’t too surprising because I probably have full sun in only 10% of my garden. While visiting a local garden center I wanted to buy a few sun perennials, but I was overwhelmed at the choices. I opted for a few blooming sages. After reading this article, I’ll add other flowering perennials in the coming months with an emphasis on staggered bloom times. Bottomline? Add/have a wide array of blooming plants to help the pollinators. I hope you find the article informative. I certain did.] 

Pollinators have immense value to agricultural food production, plant reproduction and ecosystem health. Pollinators are directly or indirectly involved in the agricultural production of roughly 30 percent of the food and drink we consume. Thus, many are greatly concerned about reports that pollinators are in decline.

Common pollinators include bees, wasps, ants, flies, butterflies, moths, beetles, birds and bats.

Research suggests that gardeners can play an important role in supporting pollinators. For example, the abundance of flowering plants was shown to be one of the strongest predictors of bee and butterfly diversity in New York City community gardens (Matteson and Longellotto, 2010). Similarly, the number of shrubs in a garden was found to be the strongest predictor of butterfly diversity in Paris (Shwartz et al., 2013).

In the not too distant past, it was thought that most, if not all plants and their pollinators had co-evolved, so that particular plants attracted specific pollinators, and that specific pollinators would only visit particular plants. This view of plant-pollinator relationships has led many to recommend that pollinator gardens rely on native plants. However, ecologists now recognize that most plant-pollinator relationships are much more promiscuous than was previously thought. In fact, bees and butterflies have been found to heavily utilize exotic ornamental plants in urban gardens, even when native plants are present (Frankie et al., 2009; Matteson and Langellotto, 2011).

Thus, it is not as simple as saying “Choose native plants when building a pollinator garden.” Instead, the savvy landscaper should adopt a few simple rules when selecting plants to feature in a pollinator garden:

1. Plant lots of flowering plants. Using a wide variety of floral colors and shapes in your garden will attract more pollinators. Group like flowers together. They’re more likely to catch the attention of passing pollinators.
2. Choose plants that bloom from early spring through late fall. Especially in early spring, pollinators that are active may have a hard time finding food. Thus, spring-blooming plants can have a large impact in attracting and conserving pollinators. Of course, summer and fall-blooming plants provide resources for pollinators that arrive later in the season.
3. Provide host plants for butterflies and moths. Butterflies and moths usually prefer to feed on nectar, but their young need to feed on plant leaves. Native woody ornamentals are great host plants for many species. Worldwide, more than 500 species of butterflies and moths feed on various oak species; and Vacciniums host nearly 300 species. A little over 200 butterflies and moths develop on various elms with the genus Ulmus.
4. Use native plants, but don’t discount the value of attractive exotics. Native plants are often recommended as a means to attract and/or conserve wildlife in urban areas, in large part, because they are fantastic host plants for the larvae of a variety of butterflies and moths. However, research suggests (Matteson and Langellotto, 2011) that exotic garden plants (particularly annuals and smaller perennials) are used by, and important in maintaining the diversity of butterfly and bee communities. In addition, [the research] found that additions of native plants need to be much more substantial than most sources recommend, if they are to significantly influence butterfly and bee diversity in gardens.

Based on her research, the author suspects that the conservation value of installing a few native plants (other than native trees) in the garden is often oversold, while the value of installing a few exotic plants that are highly attractive to bees and butterflies is often undersold.