What’s All the Buzz? Woody Plants for Bees, Butterflies, and Other Bee-t-full Pollinators

Article Contents

Overview

What makes a flower attractive to a pollinator?

How can we help pollinators?

Which plants attract pollinators?

Pollinator Plants by Bloom Time:

– Mid to Late Summer

– Early to Mid Fall

Vines for Bees

Evergreens that serve as a food source for butterfly/moth larvae

References

Overview

Pollinators are very important throughout the world. Over 80% of the world’s flowering plants require an insect or animal to move its pollen. In particular, insects pollinate 2/3 of the world’s crops and account for 1/3 or more of the food we eat. Insect pollinators include bees, wasps, butterflies, moths, beetles, flies, ants, and true bugs (Hemiptera). Other animals pollinate flowers, including bats and our native ruby-throated hummingbird. Many bird species utilize insects, especially caterpillars and larvae to feed their young. Fruit and seeds produced after pollination and fertilization of the flowers comprise around 25% of the diets of birds and mammals, hence pollination of these crops is critical for their survival.

Bees are considered the most important pollinator responsible for pollinating $235-577 billion worldwide and $24 billion in U.S. food crops each year, especially our fruit and some of our vegetable crops. Honey bees make honey that is a delicacy in any kitchen. Wisconsin has over 400 species of native bees that are responsible for pollinating many plants. Unlike honey bees and bumble bees, most native bees do not live in large colonies. Instead, most of them are solitary and construct their nests below ground in burrows or above ground in cavities or hollow stems. Unfortunately, both native bees and introduced honey bees and other pollinators are facing significant declines in their population due to loss of habitat and habitat fragmentation, diseases and mites, poor nutrition due to plant monocultures (lack of diverse food sources), climate change, pollution, excessive pesticide use or misuse, especially neonicotinoids and for honey bees, poor management practices.

What makes a flower attractive to a pollinator?

Bees

Bees are attracted to bright white, yellow, blue, and purple flowers that bloom during the day, have a mild to sweet or minty fragrance, and possess a nectar source. Bees are unable to see the color red. Bees commonly pollinate flowers that are tubular-shaped or with a shallow, landing platform. Ultraviolet light reveals nectar guides that point to the nectar source near the center of the flower.

Wasps

Wasps are attracted to dull-colored white or yellow, sweetly scented flowers with a nectar source. Wasps are often attracted to flowers that are less attractive to bees and butterflies. They are the primary pollinators of figs, orchids and other flowering plants. In addition, wasps can be predators and parasites of various insects, including the tomato hornworm.

Butterflies

Butterflies are attracted to red, orange, yellow, pink, and purple flowers that bloom during the day that either have no fragrance or have a spicy fragrance and produce lots of nectar. Flowers visited by butterflies have a narrow tube or are wide, flat-topped or in clusters with smaller flowers that provide a landing pad for the insect. Spots, lines, and blotches in flowers or near the center of the flower can act as nectar guides for butterflies.

Moths

Moths are attracted to dull colors or white flowers that are very fragrant and produce lots of nectar. The flowers open later in the afternoon or at night, though, some moths are active during the day. Flowers are often in clusters that provide a landing platform.

Beetles

Beetles are found on a variety of flowers, but are strongly attracted to day-blooming, large, bowl-shaped, green or white flowers with exposed stamens and pistils, like a magnolia flower. Flowers can also be in clusters with small, individual flowers. The flowers often have a strong spicy or fruit-scent and nectar may or may not be present.

Flies

Flies are attracted to smaller, pale, dull to dark brown or purple flowers, often with a putrid scent. Flies are attracted to shallow, bowl-shaped, funnel-like or trap-like flowers that bloom during the day and/or night. They rarely are attracted to flowers with nectar, but the flowers provide lots of pollen. Some fly species, called hover flies or syrphid flies, mimic bees in their appearance.

Ants

Ants, though not as important for pollination as the above insects, visit low-growing, small, inconspicuous flowers positioned close to the stem with a nectar source. They do not tend to have a color preference.

Hummingbirds

Hummingbirds are notoriously attracted to day-blooming flowers with bright colors such as red, orange, yellow, and pink, though, they will visit blue and purple flowers. The flowers are typically large, funnel or cup-shaped, or tubular. Flowers do not need to be fragrant, but they must produce lots of nectar. Some hummingbirds also feed on small insects. Their nests are often in nearby trees, protected from predators.

How can we help pollinators?

These steps below can be taken by communities and individuals to help pollinators’ populations thrive in our urban and rural environments.

Plant a wide variety of trees, shrubs, perennials, and annuals with overlapping and sequential blooming periods throughout the entire growing season. Trees can provide a good source of protein-rich pollen in early spring when bees are laying their eggs. Throughout the summer, bees require both nectar and pollen. Spring pollen and nectar are important for overwintering bumble bee queens that need to feed themselves and their first young, but also spring bees, such as orchard bees, that are only active in the spring. Other pollinators, such as butterflies, moths and wasps, use nectar from flowers as a carbohydrate source.
Plant the right plant in the right place: Choose plants that are appropriate to the area you are planting to reduce the incidence of diseases and insect pests. Whenever possible, choose plants that are cold-hardy, non-invasive, including native and non-native plants and cultivars that may have improved resistance to insect pests and disease pathogens.
To attract as many pollinators as possible, choose both woody and herbaceous plants with different colored flowers, shapes, and sizes, but avoid double flowers that have the pollen and nectar sources hidden or absent. Plants that produce only sterile flowers, such as some cultivars of hydrangeas, do not attract pollinators. Flowers do not need to be large as tiny flowers produced in clusters attract a number of pollinators.
Keep plants healthy with proper watering, mulching, and pruning. Fertilize only if a soil and/or foliar test indicates a need and use slow-release nitrogen (N) fertilizers to avoid excessive soft, succulent growth that is more susceptible to insect feeding. Some areas in southern and eastern Wisconsin typically have soil with plenty of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) and may only require supplemental nitrogen (N).
If an insect or disease problem occurs on your plants, think twice before reaching for the pesticide shelf. Many insects and diseases cause cosmetic problems that are not serious enough to warrant spraying. If in doubt as to whether to spray or not, consult an International Society of Arboriculture (ISA) certified arborist, extension agent or educator, or trustworthy person in the Green Industry who knows what the pest is and how to manage it, preferably without pesticides. An integrated pest management (IPM) approach that uses chemicals only as a last resort will go a long way toward protecting our birds and pollinators.
Do not forget to plant larval host plants for caterpillars, especially in early spring. If you want monarch butterflies in your garden, you will need to plant our native milkweeds as this is the only group of plants that the larvae will feed upon. Other host plants for other pollinators include trees, shrubs, vines, and other herbaceous plants including bulbs.
When bees are pollinating flowers, reduce or avoid the use of pesticides, especially broad-spectrum insecticides. Avoid spraying trees during bloom time, especially when lindens and fruit trees are in bloom as these trees are some of many bees’ favorite choices for food. Even fungicides and herbicides not intended to kill insects, can still harm pollinators’ reproductive capacities, foraging ability and longevity.
Avoid pesticide dusts, long-residual and systemic pesticides. Instead, try to use the lowest risk and lowest labeled concentrations of pesticides. Even organic pesticides can be highly toxic to bees and other pollinators. Always read the label and within it the advisory box regarding when the product can be applied to protect pollinators.
Provide more food choices for pollinators. Monoculture yards that consist mainly of turfgrass do not help pollinators. Plant a variety of trees, shrubs, evergreens, vines, groundcovers, bulbs, herbaceous perennials, herbs, fruit, vegetables, and annuals to provide diverse sources of pollen and nectar. Plant flowering plants in large patches to attract pollinators rather than small patches.
Try to retain or create undisturbed, bare soil for ground nesters. Minimize soil disturbance in untilled areas, and clear away some plants from well-drained slopes.
Provide shelter for pollinators, including hummingbirds. Many pollinators will shelter from bad weather conditions and predators in trees, shrubs and nearby ornamental grasses and other tall herbaceous vegetation.
Provide cavities by retaining a part of an old, dead tree trunk or branches, or create artificial, small, wooden bee boxes drilled with holes and hung on the side of trees or placed strategically in the yard on a post in a sunny, open space. Bundles of hollow stems from bamboo, reeds, or woody stems, can also be used and are perfect for solitary bees. Cut stems into 4-6” long pieces and bundle them together with wire or strong twine. Create nesting sites for bumble bees with the use of native bunch grasses and maximize wild spaces.
Provide a clean water source somewhere in the yard for pollinators and birds. Birdbaths, fountains, ponds, decorative trays, and dishes set on long stakes placed in the yard that can hold at least an inch of water will attract birds and pollinators at the edges of the water. Make sure to keep the water reservoir refilled on a regular basis with fresh, clean water, which will help deter mosquitos from laying eggs. Use a small fountain, bubbler, or solar-powered water circulator in the water source for agitation to also deter mosquito egg laying.
Delay spring garden cleanup until later in May as insect pollinators overwinter in hollow flower stems and plant debris on the ground. Refrain from mowing dandelions and other early spring flowering plants early in the season.
In autumn, avoid trimming back perennial plants. The hollow stems will provide shelter for overwintering insects. These plants may have seed clusters that help feed small mammals and birds.
Leave a layer of fallen leaves in garden beds as this provides shelter for overwintering pollinators and other beneficial insects. Avoid shredding the leaves with the lawnmower. Shredded leaves will not provide adequate leaf cover for pollinators compared to leaving the leaves intact as eggs, caterpillars, and cocoons will be destroyed. Use a rake or leaf blower to move leaves off the grass and into beds or around trees. To keep the leaves in place, use temporary short fencing or chicken wire around the beds or trees, or put the leaves into your compost pile. The addition of an organic mulch layer in the fall, such as leaves, provides essential nutrients to the soil as it decomposes and improves soil structure with the addition of organic matter. Early spring germinating weed seeds will be suppressed and soil moisture is better maintained during the growing season with the addition of an organic mulch.
For growers and garden centers, provide sales areas and signage for plants that attract pollinators. This can provide increased marketing and sales for your business throughout the season. Homeowners need guidance in their plant selections particularly for attracting pollinators.

Which plants attract pollinators?

Most recommendations for species to plant to attract pollinators have focused on annual and native perennial species with little regard for woody trees and shrub species. However, a single tree or shrub can provide thousands of flowers with high quality pollen and nectar. Research conducted by Mach and Potter (2018) reported different woody plants that attract different bee communities. Some woody plants attract many different bee species, only few bee species or none at all. They also reported both native and non-native plants attract diverse communities of bees and other pollinators.

The research demonstrated that flower architecture matters. Flowers with single row to semi-double rows of petals (more petals, but not fully double) with exposed reproductive parts were more favored by bees and other pollinators than plant species and cultivars with double flowers (no visible reproductive structures in center of flower). Flowers with only sterile flowers (lacking reproductive structures or are genetically sterile through breeding efforts) or with double flowers do not attract bees or other pollinators as they cannot access the pollen or nectar. Further, analysis of the pollen and nectar from bee-attracting, native and non-native plants showed the nutrients varied by plant species, but there were no significant differences between native and non-native woody plants thus both can provide the same quality food for bees and other pollinators.

Below is a list of tree, shrub, evergreen, and woody vine species that are known for their source of either pollen or nectar critical to sustaining pollinator health and survival. This list is not a complete list but includes species that were reported to attract pollinators. There are many other native and non-native herbaceous perennials and annuals that attract pollinators but are not included below due to space limits.