Non-native plants can be just as attractive to pollinators.
November 12, 2018 By Dr. Sarah Jandricic Lauren Vanderlingen Caitlin MacDonald and Rodger Tschanz
In Greenhouse Canada’s August “New Varieties” edition, experts from garden centres reported that eco-friendly plants are a trend that’s here to stay, especially for the newer generation of gardeners. Topping the list for these millennial gardeners are plants that are considered “pollinator-friendly”.
Generally, “pollinator-friendly” means any plant that provide bees, flies, butterflies and other beneficial insects with readily available nectar (a sugar source) or pollen (protein) that helps sustain their populations. With all the stressors on pollinators these days – diminishing and fractured habitats, climate change, and ubiquitous pesticides – urban gardeners can provide native bees and other pollinators with a helping hand by planting high quality resources. As such, plants labelled as pollinator-friendly should continue to sell well in Ontario. A study by our close neighbours in Michigan State, shows that many consumers are even willing to pay a premium for “bee-friendly” plants, especially for outdoor flowering plants.
So which plants should consumers – and therefore growers and garden centres – be choosing if they want to stay on top of these trends, and support Ontario’s pollinators?
The University of Guelph and the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) joined forces for a two-year study at the Guelph Trial Gardens (located at the Guelph Turfgrass Institute) to answer just this question. Undergraduate students Caitlin MacDonald and Lauren Vanderlingen patiently watched flowers for hours at a time, to determine which plants were most attractive to what sorts of pollinators. A visit from a pollinator was considered successful if the insect in question entered the centre of the flower and stayed there for a few seconds to gather nectar or pollen. They investigated both plants considered “native” to North America, as well as species which could be considered “exotic”, or non-native, with these broken up evenly into annuals and perennials, to determine if there were any major trends.
Over the two-year study, our students saw no difference in total abundance of pollinators on native versus non-native species of plants (Fig. 1). But, much of this was due to “stand-out” performers in each category (Fig. 2), i.e. plants that attracted hundreds of pollinators over their period of observation. Many of these were perennials, but there were quite a few annuals that attracted a plethora of pollinators, too.
In 2016, top-performing non-native plants were cosmos, Argyranthemum, and Sedum. These plants attracted an abundance of managed honey bees (Apis mellifera), bumble bees, as well as hover flies (important pollinators, AND often natural predators of pests). Cosmos also attracted the highest numbers of native bees across the two years of our study, which included species of sweat bees, leaf cutter bees, small carpenter bees, and long-horned bees. These exotic plant species were also highly attractive to pollinators in 2018, along with dianthus, which attracted large, charismatic pollinators like butterflies and hawk moths in our studies.
As for native species, Heliopsis and Helianthus were favourites of managed honey bees and hoverflies in 2018 (Fig. 2). Cultivars of Echinacea (including Summer Sky, Cheyenne Spirit and Eccentric Yellow) were also unsurprising general favourites across both years, attracting a wide range of pollinators, including pollinating beetles. Other stand-out native plant species can be found in Table 1.
Given that all these plants have similar flowering times and were all attractive to pollinators in the peak of summer (see Fig. 1), retail markets could potentially produce a mixture of these native and non-native plants to be retailed as “pollinator-friendly” planters or seedling trays, as a value-added option.
Despite our results, the top 10 websites from a Google search of “pollinator-friendly plants, Ontario” generally promote native plant species only, like goldenrod, milkweed, and black-eyed susan, which are more commonly available as seed – not from your local grower or retail market. Although lists like these are doing their best to support our pollinators, they don’t help support Ontario’s greenhouse floriculture industry. Such lists also commonly focus heavily on perennials, and miss out on informing gardeners on which annuals they can purchase to add dimension and interest to their garden year to year, and still help out their bee friends.
To help bust the myth that only plants native to Ontario are good for our pollinators, the information from our study was shared with members of the public and the Canadian Nursery and Landscape Association (CNLA) at the Guelph Trial Gardens Open House in August. Flowers Canada (Ontario), will also be updating their pollinator-friendly plant poster so consumers and avid gardeners know to include relevant non-native and annual plants in their gardens.
Lastly, don’t forget that “pollinator-friendly” also means producing the plants in a way that doesn’t hurt sensitive beneficial insects. This means avoiding the use of neonicotinoid insecticides, like imidacloprid and acetamiprid as much as possible. If needed, plants should be drenched no later than five weeks before sale. Plants in flower should not be sprayed with any insecticide three weeks before shipping.
Sarah Jandricic, PhD, is the greenhouse floriculture pest management specialist for OMAFRA. Rodger Tschanz is the trial garden manager at the University of Guelph. Caitlin MacDonald and Lauren Vanderlingen were part of the Undergraduate Student Experiential Learning (USEL) Program through OMAFRA-UofG.
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