This week is National Pollinator Week. It is amazing that something as small as a bee is vitally important to our food supply. As pollinators, bees transfer pollen thus ensuring that plants and crops develop fruit and seeds for us to consume. But bees are not the only keystone species that we depend on, we also need other pollinators such as butterflies, moths, beetles, flies, and birds, including hummingbirds. About 80 percent of the world’s flowering plants depend on pollinators (the others are wind pollinated). According to Cornell University, pollinators are responsible for every third bite of food we eat. Unfortunately, pollinator populations have declined due to pesticides, habitat loss, and disease. Gardeners who are aware of this problem have deliberately planted flowering perennials and annuals to provide pollen (protein) and nectar (carbs). Because of their dramatic 90 percent decline in population over the past 20 years, monarch butterflies have received quite a lot of support. Many gardeners are planting milkweed – the one and only plant for monarchs — or trying to produce more butterflies with home kits. Bees too have received national attention. Nurseries promote bee friendly flowers and gardeners have planted bee magnets such as Joe-pye weed (Eupatorium), goldenrod (Solidago), and gayfeather (Liatris).
These efforts have helped the pollinators and certainly gardeners have come to appreciate the importance of pollinators. However, an overlooked source of food and protection for pollinators are trees. Trees provide more flowers, plenty of foliage for larva (caterpillars), and a large infrastructure to hold hives and nests. Because of the number of flowers a canopy provides, trees can provide more pollen and nectar compared to annuals and perennials. Plus, as homeowners move from house to house, the herbaceous landscape may change but usually the trees and all of their tiny inhabitants remain.
Plant Small Native Trees for Homes
“Trees are a permanent fixture,” said Steve Nagy, an International Society of Arboriculture (ISA) Board-Certified Master Arborist and Assistant District Manager at the northern Virginia office of the Davey Tree Expert Company. Based in Ohio, the company was founded in 1880 and has offices across North America.
For attracting pollinators in the Washington DC metro area, Steve recommends native trees that thrive in our particular climate (cold winters and hot, humid summers). “We recommend native trees because the chances of them growing well is higher that non-natives,” he explained. For typical suburban lots where space is a premium, Steve recommends swamp white oak (Quercis bicolor), willow oak (Quercis phellos), post oak (Quercis stellata), cucumber magnolia (Magnolia acuminata), sweet bay magnolia (Magnolia virginiana), black gum (Nyssa sylvatica), little leaf linden (Tilia cordata), persimmon (Diospyros virginiana), and serviceberry (Amelanchier). “Sourwood (Oxydendrum arboreum) is a great tree, too,” said Steve, “It is a typically overlooked native with good fall color.”
Plant Trees that Flower at Various Times
While a tree can provide many flowers, usually it only flowers for a few weeks. Because different pollinators are active at various times of the year, Steve recommends planting trees with various bloom times. Instead of planting the well-known spring bloomers such as flowering cherry trees, flowering plums, star magnolias, saucer magnolias, and redbuds, homeowners can plant summer blooming trees such as little leaf linden, persimmon, cucumber magnolia, southern magnolia (Magnolia grandiflora), and crape myrtle (Lagerstroemia).
Plant Trees that Support Specific Pollinators
Another reason to plant trees is that certain pollinators require specific tree species or genera. Similar to the monarch butterfly’s relationship with milkweed, the spicebush swallowtail caterpillar only feeds on spicebush (Lindera benzoin) and sassafras (Sassafras albidum). The zebra swallowtail caterpillar only feeds on young paw paw leaves (Asimina spp.) and the pink-striped oak worm moth gets its name from its preference for oaks (Quercus spp.).
Plant Trees in the Fall
Although this week is National Pollinator Week, summer is not the best time to plant trees. Because trees take longer to become established than perennials and annuals (larger plant hence more root structure and more foliage), Steve said the best time to plant trees is in the fall. “If you can get planting done by Mother’s Day,” said Steve, “the tree has a chance to make it through the hot summer but fall is the best time.” Steve also recommends to plant smaller rather than bigger but one can plant bigger plants in the fall. Fall, as opposed to spring or summer, offers warm soil but cooler temperatures, thus the amount of transpiration or water loss is less. The tree can devote energy into root establishment, not making up for water loss due to heat.
For information on how to plant a tree correctly, the Davey website has an extensive collection of articles and videos on tree planting and maintenance. If you need more personalized assistance, Steve mentioned that homeowners can request a free consultation by calling or completing a form on the website. A certified arborist can come to one’s home to evaluate the trees and landscape and devise a strategy to meet the goals for that specific property.
This week, celebrate National Pollinator Week by learning more about pollinators, identifying the best plants and trees for pollinators in your area, and incorporating best practices to protect, harbor, and feed pollinators.
This article was originally published on June 18, 2018, and now has some modifications.