Over time, flowers have been bred with characteristics like double petals or bold colors to appeal to consumers.

Although this breeding produces flowers that are more desirable to humans, it can simultaneously produce flowers less desirable to bees.

Traits humans find desirable, such as doubling the amount of flower petals or making plants bloom continuously, can obscure or even eliminate a bee’s access to a flower’s pollen or nectar.

Since there are very little data on which environmental horticulture plants remain attractive to bees, our researchers are measuring the pollinator attractiveness level of various environmental horticulture plants. The selected plants include multiple culitvars of the top annuals and herbaceous perennial plants.

Research Question

Which environmental horticulture plants are most attractive to bees?

Research Plans

Girl sitting and taking data next to rows of pink flowers, taking pollinator attractiveness data.
2017 Plots of annual flowers at Michigan State University for pollinator attractiveness experiment. (Photo by Erica Hotchkiss.)
Flower experimental plot at San Diego Botanic Garden
Native and non-native herbaceous plants at San Diego Botanic Garden, ready for data collection. (Photo by James Bethke.)

Bee visits to flowers

We are recording bee visits on annual herbaceous plants, perennial herbaceous plants, and woody plants. Within certain sites, we are also comparing bee visits between native and non-native plants.

For annual and herbaceous plants, we planted five experimental gardens throughout the United States. Each garden was planted with a selection of environmental horticulture plants and cultivars, all picked from the list of top 25 annuals and perennials sold in the year 2014 according to the National Agricultural Statistics Service’s (NASS) Census of Horticulture.

For woody plants, we surveyed 72 environmental woody plant species located throughout various urban and suburban locations.

To compare bee visits between native and non-native herbaceous plants, an experimental garden of 18 environmental horticultural and potential environmental horticultural plants was established. About half the plant species were native to California, while the remaining half were non-native. To compare bee visits between native and non-native woody plants, we compared bee visits from the same environmental horticulture woody plant species surveyed throughout various urban and suburban locations.

Researchers: Drs. Jim Bethke, Christine Casey, JC Chong, Christina Grozinger, Harland Patch, Dan Potter, Dave Smitley, Kim Stoner

States: CA, CT, KY, MI, PA, SC

9 petri dishes on a lab table, each filled with pollen 'pellets' taken from honey bees.
Pollen collected from honeybees sorted into petri dishes according to color. (Photo by Kim Stoner.)

Pollen analysis

Honey bees depend on pollen to feed their young. When adult honey bees collect pollen, they pack it onto their hind legs, forming pellets of pollen. By analyzing these pollen pellets with DNA and microscopic techniques, we can identify what plants the honey bees visit most for pollen.

To collect honey bee pollen, we’ve placed various honey bee hives near nurseries and throughout an urban landscape. By using pollen traps—structures that allow bees to enter the hive but knock off the pollen they gathered on their hind legs—collect the pollen. We then split each sample and either 1) looked at it under the microscope to identify unique pollen morphology or 2) extracted DNA and compared it to known DNA markers (“DNA fingerprinting”). Both techniques can generally identify which plants the honey bees have visited.

Researchers: Drs. Christina Grozinger, Harland Patch, Douglas B. Sponsler, and Kim Stoner

States: CT, PA

Additional Research Areas

Research Updates

  Strong biodiversity is an important factor in maintaining healthy landscapes, wild and agricultural alike. There is a plethora of research that suggests high flowering plant abundance promotes a high pollinator abundance. Some of these studies included biodiversity studies along ecological margins, which are essentially the boundaries between two plant communities. A classic example would […]

While pollinators are in decline, partly due to lack of plant resources, urban, semi-natural, green landscapes have become important resources for pollinator survival. Erica Erickson, a PhD student at Penn State, asked the question of what role, if any, ornamental plants play in the sustainability of the pollinator community? Pollinator visitations from two sites in […]

In January 2020, Nature Research Journal published a scientific report from Sponsler et al. that highlights the importance of pollinator-friendly woody plant genera.  In managed greenspaces, it is often assumed that pollinator communities are supported by a variety of ornamental horticulture. However, Sponsler and our pollinator team members know that many ornamental plants are simply [...]

Agastache foeniculum flower

In the fall of 2018, our team completed another field season tracking the environmental horticulture plants that are visited by pollinators. Some preliminary patterns are now starting to emerge, with a few plant species appearing to be highly attractive to pollinators, but many other plant species are not-at-all attractive to pollinators. In California, for instance, [...]