The surrounding terrain has very little influence on the abundance, diversity and composition of pollinators
New research shows that bees in particular don't really care about the landscape around flower gardens. (Photo: USDA, Public Domain)
KNOXVILLE, Tenn. (THE CONVERSATION) – Most flowering plants rely on animals to transport their pollen to reproduce. Pollinators, in turn, rely on flowers for food, including both nectar and pollen. If you are a gardener, you may want to support this partnership by planting flowers. However, if you live in an area without much green space, you may be wondering if it's worth the effort.
I study bees and other pollinators. My new research shows that bees in particular don't really care about the landscape around flower gardens. They seem to focus on the specific types of flowers they like, no matter what else is around.
To design a garden that supports the greatest number and diversity of pollinators, you don't have to worry about what your neighbors are doing or not doing. Just focus on planting different types of flowers – lots of them.
Comparison of different landscapes
To test whether there are more bees in natural areas, my team and I planted identical gardens — about 3 by 2 meters (10 feet by 6½ feet) — in five different landscapes around East Tennessee, ranging from livestock pastures to organic -Farms ranged from botanical gardens to gardens and an arboretum. All five gardens were created in March 2019 and contained 18 species of native perennials from the mint, sunflower and pea families.
As the flowering period progressed, we studied pollinators by collecting the insects that landed on the flowers so we could count and identify them. Sampling was carefully standardized. Every week we tried every flowering plant in every garden, in every landscape, for five minutes each. We used a modified handheld vacuum cleaner that we called the “Bug Vac” and repeated this sampling every week while the flowers bloomed for three years.
We wanted to test whether the area immediately surrounding the gardens – the flower district – makes a difference in pollinator abundance, diversity and identity. Therefore, we also examined the area around the gardens within a radius of about 160 feet (approximately 50 meters).
To our surprise, we found that the surrounding terrain had little impact on the abundance, diversity, and composition of pollinators that came to our test gardens. Instead, they were determined primarily by the number and type of flowers. Otherwise, pollinators were remarkably similar at all sites. A sunflower in a cattle pasture had broadly the same number and type of visitors as a sunflower in a botanical garden.
Menu planning for pollinators
We used native perennial plants in our study because there is evidence that they provide the best food for insects visiting flowers. We chose from three plant families because each offers different nutrients.
Plants from the mint family (Lamiaceae), for example, provide a lot of sugary nectar and have easily accessible flowers that attract a wide variety of insects. I would recommend including plants from the mint family if you want to provide energy for flight to a large and diverse group of insects. If you live in Tennessee, some examples include mountain mint, wild mint, and Cumberland rosemary. You can easily search for perennial plants that are native to your area.
While some pollinators enjoy nectar, others get all their fat and protein only from the pollen itself. Flowers in the Asteraceae family, including asters and coreopsis, provide large amounts of pollen and nectar and are also very easy to access. Plants in this family are well suited to a range of pollinators, including many specialist bees, such as the blue-eyed longhorn bee (Melissodes denticulatus), which feeds primarily on verbena (Vernonia fasciculata), also a member of the sunflower family.
If you want to offer flowers with the highest protein content to feed the next generation of strong pollinators, consider plants in the pea family (Fabaceae) such as dwarf indigo, false indigo and bush clover. Some plants in this family don't even offer nectar as a reward. Instead, they provide protein-rich pollen that is only accessible to the most effective pollinators. If you grow plants from the pea family in your garden, you may see fewer visitors, but they will receive high protein pollen.
A good place to start is by selecting a few native perennials from each of these three families, all of which are widely available in garden centers. Just as a variety of foods is important for human health, a mix of different types of flowers provides pollinators with a varied and healthy diet. Interestingly, the diversity of the human diet is directly related to pollinators, as most of the color and diversity of the human diet comes from plants pollinated by insects.
Plant it and they will come
You may have heard that the number and diversity of insects is declining worldwide. This problem is of particular concern for humans, who rely on insects and other animals to pollinate food crops. Indeed, pollinators face many threats, from habitat loss to pesticide exposure.
Luckily, gardeners can do these precious animals an incredible service by simply planting more flowers. As our research shows, small patches of garden space can help increase pollinator numbers—even when the surrounding landscape offers few resources for them. The one constant in all of our research is that insects love flowers. The more flowers and the more species of flowers there are, the more pollinators there will be on earth.
–Laura Russo
University of Tennessee
The conversation