Perry's Perennial Pages
Evaluating Flowering Plant Selection for Pollinator Habitat
Enhancement: Open-Pollinated Natives vs. Native Cultivars
Annie White (graduate assistant) and Dr. Leonard Perry, University of Vermont
The objective of this study is to
compare open-pollinated native flower species to native cultivars, in terms of
their ability to attract and support native pollinators.
Species richness and abundance of native pollinators will be measured to
assess flower attractiveness and nectar and pollen availability will be measured
to determine the plantís ability to support pollinators.
A native plant is defined by the USDA
and NRCS as a plant that is a part of the balance of nature that has developed
over hundreds or thousands of years in a particular region or ecosystem. Only
plants found in this country before European settlement are considered to be
native to the United States. This
research will focus on flowering herbaceous plants native to the New England
The project will begin with an informal
survey of plant nurseries in Vermont to assess the current interest and
commitment to growing and selling native plants; issues with native plant
availability; prominence of true native (open-pollinated, local genotype) plants
versus native cultivars; and which species are most commonly grown and sold.
A minimum of ten native herbaceous perennial species will be selected for
the study and will be compared to common Ďimprovedí cultivars of the same
Cultivars will be chosen for the study
based upon their popularity in the retail garden market, bloom period (early,
mid, and late-season bloomers), and method in which the cultivar was
established. When possible, one
cultivar will originate from a natural selection and the second cultivar will
originate from a controlled cross. Each pollinator garden will therefore contain
a total of 30 plant types (ten plant species with one open-pollinated type and
two cultivars). Nine individual plants will be planted for each plant type,
forming an approximately one by one meter plant block within each garden. Each
garden will be approximately 37 square meters (400 square feet).
Plants will be obtained in quart or gallon-sized pots from plant
suppliers. Efforts will be made to obtain open-pollinated native plants with
genotypes most local to the study sites in northwestern Vermont.
Using the selected species, pollinator
gardens will be designed for three study sites. Two of the study sites will be
situated on the properties of cooperating farmers, River Berry Farm in Fairfax,
Vermont and Full Circle Gardens in Essex, Vermont, and a third study site will
be located on the University of Vermont campus.
The study sites were chosen for the diversity in their immediate
surroundings (fruit and vegetable crops, plant nursery, and urban campus),
diversity in the greater surroundings (agricultural, residential/forested, and
urban/suburban), and their ability to support the educational objectives of the
study. The diversity in sites for the pollinator gardens will allow for
comparisons not only between open-pollinated natives and native cultivars (and
the method of cultivar selection), but also between site variables such as
competing nectar/pollen availability and landscape surroundings.
To control for environmental variables,
each pollinator garden will contain both the true native and the native
cultivars. The design of each garden
will vary slightly based upon the site constraints and opportunities to display
the plant material to the public. The pollinator gardens will serve to provide
valuable data and will also serve to educate visitors to the sites. The
farmstand and greenhouse at River Berry Farms, the retail plant nursery at Full
Circle Gardens, and the University of Vermont campus are open to the public and
have regular visitors, who will be able to tour the perimeter of the pollinator
gardens and learn about the value of native plants and pollinators from
interpretive signage. Each plant
species and cultivar will be clearly labeled and additional educational signage
will be designed and installed.
During the first growing season,
ongoing maintenance of the study gardens, including watering and weeding as
needed will be performed. Preliminary
field surveys will be conducted in year one to assess species richness and
abundance of native pollinators including bees, butterflies, and hummingbirds.
This preliminary data will be used to identify the predominant pollinator
species in the research area. In
consultation with UVM entomologists and statisticians, the most rigorous method
for grouping and quantifying these pollinators will be employed.
For example, due to the large abundance of native bee species and the
difficulty of identifying them in the field to the species level, it may be
deemed appropriate to group native bees into four sub-groups based upon
morphology, field-recognizability and pollination efficiency. Such groups could
include bumble bees, other large bees, green bees, and small bees, similar to
methods utilized by Winfree et al. 2007.
During the second growing season, field
data will be collected by the project manager under the guidance of the
principal investigator. Each garden
will be visited weekly throughout the blooming season (early-June through late
September). Each visit will rotate between morning, midday, and evening.
Pollinator visitation rates will be measured for native and native
cultivar flowers as pollinator visits per flower per unit time. Pollinator
visits to as many flowers as can be viewed simultaneously within each
approximately one by one meter plant block will be recorded during 60 second
scans. Each plant block will be scanned three times per garden visit.
At the visually-observed peak of each
plantís bloom period, nectar volume and sugar concentration will be measured
using a microcapillary tube and a hand-held refractometer.
Pollen mass will be measured manually. A minimum of 8 samples will be
taken per plant type at each site, totaling 24 nectar/pollen samples per plant
Collaborating entomologists, plant
physiologists, and statistical consultants from the University of Vermont will
review the proposed data collection methods and provide guidance throughout the
study to ensure the research methods are rigorous and yield statistically valid
results. The data will be statistically analyzed to determine if native
cultivars differ from open-pollinated native flower species in their ability to
attract and support native pollinators.
(This project funded through the SARE on farm/partnership research program, 2012-2014, and with support from Greenworks, Vermont-- The Vermont Nursery and Landscape Association.)