Our York Street gardens will close at 3 p.m. on Thursday, May 5 for Spring Plant Sale Preview Party.
Last week a colleague and I attended a conference and workshop about protecting native pollinators, hosted by the Xerces Society for Invertebrate Conservation. While most of us might think of the European Honeybee, Apis mellifera, as the primary pollinator of crops, native bees are important pollinators of both wildflowers and commercial crops.
Native pollinators, and particularly native bees, are important. Some are highly specialized, like the squash bee. Squash bees rely exclusively on squash flowers for sustenance and along the way do a very thorough job of pollinating them. By some estimates this bee alone pollinates up to 70% of squash. In addition to taxonomic specialization, many native bee species are active during cool and wet periods when honeybees won’t leave the hive. And on a per bee basis, natives are oftentimes better at pollinating than their introduced counterparts. For example, between 250 and 750 blue orchard bees, Osmia lignaria, can pollinate an acre of apple trees. It would take 10,000 to 25,000 honeybees to do the same job.
Native pollinators like the squash bee and blue orchard bee are becoming more important as honeybee populations continue to decline under a variety of stresses (including Colony Collapse Disorder) and cropland requiring pollination increases (it’s doubled since around 1950).
Unfortunately, native bee populations are also in decline. Many species of bumblebee are facing extinction, and bees and other native pollinators all face loss of habitat and food sources. Luckily, home gardeners can make an impact on the health of native pollinator populations including native bees. Pollinators don’t require much—a place to eat and a place to build a nest are really about it.
To provide food, plant long-blooming flowers wherever you can, and (importantly!) don’t use pesticides on them. Some evidence suggests that native bees prefer native plants if given a choice, but by all accounts they will use whatever is available. Focus especially on very early and late blooming plants, as native bees are often active earlier in the spring than honeybees.
For shelter through the winter, many native bees use tussocks of grass, hollow stumps, or piles of detritus. Consider intentionally leaving some ornamental grass uncut and areas of your yard less manicured to encourage hibernating residents. During the summer, you can provide nesting places for mason and carpenter bees by leaving dead wood or reeds about or by providing a more stylish nesting box, which are easy to make and widely available commercially. If you are lucky enough to have ground-dwelling bees on your property, don’t disturb them—it’s difficult to re-create their preferred nesting habitat.
If you would like to find out more about protecting native pollinators in your area, please visit the Xerces Society website, the Helen Fowler Library at Denver Botanic Gardens, and keep a lookout for pollinator classes periodically offered at the Gardens.