Pollinator Gardening Principles
Photo: Syrphid fly on blue-eyed grass by Mark Robinson
A full-fledged pollinator habitat has many elements—below are the elements we've deemed integral to each habitat and why.
Native Plants
Nearly 90 percent of all flowering plants require the help of a pollinator to reproduce, but not just any pollinator. Native plants are species that existed here prior to European colonization, co-evolving with the animals that pollinate them. Over thousands, if not millions of years, plants and pollinators have adapted to one another chemically, physically, and phenologically. By using locally native plant species, we are creating diverse habitats that native pollinators are most likely to thrive in.
Avoiding Pesticide Use
Pesticide use is one of the leading causes of pollinator decline. “Pesticide” is an umbrella term that includes herbicides, insecticides and fungicides. Round-Up, for example, is a pesticide. A pollinator garden should not be exposed to these types of chemicals. By using a diversity of native plants, nature is better able to find balance between predator and prey, reducing the need for pest management.
Nectar & Pollen Sources
Nectar is the primary energy source for the vast majority of adult pollinators and is therefore one of the most significant elements of pollinator habitat. Likewise, pollen sources provide necessary protein for developing and adult bees. For habitat to effectively support pollinators throughout the year, there must be nectar and pollen available in all parts of the growing season (March - October).
Trees/Shrubs/Vines
Trees are meadows in the sky for pollinators, and shrubs add interesting garden structure throughout the year. In addition to providing nectar and/or pollen, woody plants, whether thriving or declining, can also offer crucial overwintering or nesting sites. Because of their mass, they are vital larval host plants for butterfly and moth caterpillars, which also serve as baby food for 96% of terrestrial birds.
Larval Hosts
Many Lepidoptera (butterflies and moths) species depend on specific native plants as food sources for their offspring. Likewise, about a quarter of all bee species rely on certain plant families or species to supply pollen for their growing larvae. Plants that act as hosts for these eggs and subsequent caterpillars (larvae), or provide pollen for bee larvae, are known as host plants. These plants can fulfill requirements in other categories as well.
Shelter
Small spaces of nearly bare, unmulched earth; dead tree snags; leaf litter left where it fell under trees; or patches of native bunch grasses can provide a place for many pollinators to nest and overwinter. NOTE: While bee hotels can be quite effective when employed and maintained properly, they also can attract parasites and harbor infectious disease when not maintained properly. Due to these potential downsides, they alone do not constitute viable shelter for this program.
Removing Invasives
Exotic invasive species can outcompete and displace native plants and are a huge threat to our natural ecosystem. Guarding your habitat against invasives promotes its longevity as a healthy refuge for pollinators and reduces the spread of these noxious species.
Limiting Exterior Lighting
Artificial outdoor lighting can be very harmful to many animals, especially moths who are incapable of resisting it. Even plants’ normal growth cycles are disrupted by artificial light—that’s why we have learned to force plants to grow and fruit abnormally quickly with grow lights. If you need lighting outdoors, use Dark Sky Approved lighting to mitigate light pollution.
Leave the Leaves... For Pollinators
For many, a leaf-strewn yard is a nuisance, a mess to be cleaned up and hauled away. Leaves are seen as a detriment to the idyllic American lawn. If you’re an organic gardener, you may look at fall leaves in a different light—you might see free, nutrient-rich mulch, and a perfect carbon source to accompany the nitrogenous kitchen scraps in your compost pile. If you’re an entomologist or a pollinator advocate, fall leaves look like something different entirely. Let’s take a look at how ‘leaving the leaves’ can support pollinators.
If you’ve ever strolled through a deciduous forest in the colder months you’ve probably noticed that, unlike the average lawn, no one rakes up the leaves. Instead, these fallen former solar panels accumulate on the forest floor and persist for many months to come. The leaves not only reintroduce carbon and other nutrients into the soil as they decompose, they also harbor their own little living world. For the smaller critters of the forest, the layer of leaves, also known as duff, can provide shelter from the elements, much-needed microclimates, camouflage, and even a crunchy, carbon-rich snack.
The majority of butterfly and moth species in temperate climates seek refuge among fallen leaves during the winter months, capitalizing on the many benefits previously mentioned. Different species of Lepidoptera (butterflies and moths) can be found overwintering in any one of the four distinct life stages these creatures occupy: egg, caterpillar, pupa, or adult. Take the red-banded hairstreak, for example—these delicate beauties lay their eggs on the underside of fallen oak leaves. When the caterpillars emerge they munch on these leaves to their hearts’ content and gear up for a harsh winter made livable thanks to their detritus home.
Lepidopterans are not the only pollinators that appreciate a leafy winter abode. Bumblebee queens burrow into the ground and rely on a layer of duff above them to keep out the elements. Unlike honeybees, these bumblebee queens will be the sole survivors of their colony, and the existence of next year’s colony is entirely dependent on her ability to make it through the winter. Seems an awful shame to rip the royal roof off of a queen’s house only to be tossed in a bag and hauled away.
Spiders, worms, nematodes, snails, and other invertebrates also occupy this under-appreciated microcosm. However, the role of fallen leaves extends even further. Leaf litter provides a crucial food source for birds that need larvae to feed their young. Even herbaceous perennial plants, waiting out the winter underground, benefit from the insulation the leaves provide their root systems. Like any other facet of an ecosystem, when the leaves are taken away, the effects radiate outwards impacting far more than just the critters that call them home.
Considering that pollinators are responsible for one in three bites of food we eat and pollinate nearly 90% of flowering plants, we need to do everything we can to protect them—leaving some leaf litter is an integral part of that process. So next time you feel inclined to get rid of those ‘pesky’ leaves, think about the butterflies, the moths, the bumblebees, and everything they do for us.