Category: sustainable gardening

Designing a pollinator-friendly garden: Tips from a pollinator expert

On By durhammastergardenersIn bees, beneficial insects, bird friendly habitat, coastal goldenrod, garden design, garden tasks, Gardening information, gardening NC, goldenrod, insects, landscaping for wildlife, native bee habitat, native plant list, native plant list for Piedmont NC, native plants, Native plants of NC, Natives, NC Native Plants, nesting bees, nesting insects, perennials, pollinator gardening, pollinators, sustainable garden design, sustainable gardening, Uncategorized, urban gardening

By Martha Keehner Engelke, NC State Extension Master Gardener SM volunteer of Durham County

Winter is the perfect time to make a plan to revise your garden. For many, that means making your garden more attractive to pollinators. Recently, I learned that building a garden that makes the A-list for pollinators is not just about the plants. I had an opportunity to interview Dr. Danesha Seth Carley, PhD Associate Professor in Horticultural Science at North Carolina State University (NCSU).

Dr. Carley’s expertise is sustainable management of urban landscapes with a focus on pollinator ecology. Her recent research programs include pollen quality in commonly planted wild-flowers, pollinator ecology, and pollinator habitat establishment.  She has conducted her research along North Carolina roadways and at the historic Pinehurst #2 and #4 golf courses.

I heard Dr. Carley speak at a program sponsored by the Gardening Association of North Carolina . I contacted her, and she graciously agreed to a follow-up interview.  She expanded on topics discussed in her presentation as well as her book Pollinator Gardening for the South: Creating Sustainable Habitats (co-authored with Anne M. Spafford)1.

orange white and black butterfly on green leaf
brown and black bee on yellow flower nectar
black and red flying insect perched on green leaf
bumblebee insect sucking nectars on flower
P
green and black hummingbird

Butterflies, bees, flies, wasps and birds are all considered to be pollinators. The most important pollinator is the bee. Bees contribute millions of dollars to the U.S. economy through pollination. (Images credit: Pixaby)

What does a pollinator want?

Let’s talk about the most important pollinator: Bees. There are two main categories of bees: social and solitary. Social bees are divided into 3 categories: bumblebees, honey bees and stingless bees (which are not well understood). Solitary bees, which are a larger category, include carpenter bees and the tiny sweat bee. In her book, Dr Carley tells the fascinating story about the social life of bees (as well as other pollinators).

The gardener needs to remember that pollinators choose plants that are best suited to their anatomy particularly tongue length (proboscis) and mouth parts. Bees are attracted to bowl-shaped flower that often have a prolific pollen ring in the middle. Native bees enjoy feasting on plants in the Asteraceae, Salix, Solidago, Helianthus, and Symphyotricum families. Butterflies and hummingbirds have longer tongues. They will be attracted to more tubular flowers such as Fuchsia (Fuchsia spp) ; Bleeding heart (Lamprocapnos spectabilis); and Turk’s cap lily (Lilium superbun).

All varieties of a particular plant are not equal when it comes to pollinators. Cultivars are often bred to maximize flower size, disease resistance, or aroma. This means that the cultivar may have less quality pollen than the plant from which it was bred. If you see the plant described as “flora pleno” (meaning with a full flower) it is likely to be a double bloom and thus less accessible to pollinators. A plant that is considered to be a great pollinator as a single, loses some of its attraction when it is a double. For example, Purple coneflower (echinacea purpurea) is one of the best plants for a pollinator garden but a number of cultivars with double flowers are more difficult for pollinators to access.

On the left echinacea purpurea has single flowers and is considered to be a great flower for pollinators. One the right, the flowers of Echinacea Supreme™ Elegance make it more difficult for pollinators to access. To some gardeners, the cultivar may seem more beautiful but the pollinators don’t see it that way. (Image credit: NC Tool Box; National Gardening Association, NJ Bob)

Someone like Dr. Carley is frequently asked which plants are the best for pollinators and she has an answer for her “Big Five” plants. They are: Mountain Mints (pycnanthemum sp.); Coneflowers (Echinacea purpurea); Butterfly Milkweed (Asclepias tuberosa); Asters (Symphyotrichum sp); and Blanket Flower (Gaillardia pulchella).

Pollinators are attracted by pollen and nectar. Desirable pollinator plants include: Mountain Mints (Image credit: ( NC Extension, Kerry Woods CC BY NC); Coneflowers (Image credit: NC Extension, Cathy DeWitt, CC BY 4.0) ; Butterfly Milkweed (Image credit: NC Extension, Mary Keim CC-BY-NC- SA-2); ; Asters (Image credit: NC Extension Douglas Goldman, USDA CC BY 4.0) ); and Blanket Flower (Image credit: elephantkitty CC BY NC ND 2.0)

The Importance of Structure/Composition

Just like humans, pollinators need two things to survive: nutrients (carbohydrates from nectar, protein from pollen) and a safe place to live and work. To be on the “A-list” pollinators want access to high quality pollen and nectar and protection from predators. This is why the structure of a garden is important.

Many of us approach gardening from the perspective of “buy one, plant one”. In our quest to have a lot of different plants, we may be reducing the attraction of our garden to pollinators. Planting clumps of plants rather than a single plant can help pollinators be more efficient. For example, honey bees and bumble bees enjoy goldenrod (Solidago). If you plant one goldenrod the female bees (the males don’t forage) collect the pollen on their hairy bodies (which is one reason they are the best pollinators), and then transfer it to their rear legs into their “pollen basket”. They mix the pollen with a bit of nectar to hold it in place and head back to the hive. If she has to do this several times because one plant doesn’t provide enough pollen, she is less efficient and it means that she might have less energy and be more susceptible to disease. There are two ways to prevent this: plant clumps of good quality plants or increase the diversity of your plantings (next section).

Goldenrod (Soldaigo spp. is a great plant for pollinators including this honey bee. When planted in clumps it helps the bees (and other pollinators) be more efficient. Of course, Goldenrod is a fast growing plant so you don’t need too many of them. (Image credit: NC Extension Plant Tool Box, Hope Duckworth)

Space for a happy home and safety from predators and toxins are other considerations related to the structure of a pollinator garden. While social bees (like honeybees) will live happily in wooden boxes or hollow trees, solitary bees dig their nests in the ground or in tubular stems. Resisting the urge to cut plants with hollow stems until the spring temperature is above 57oF (the temperature when bees become active) allows bees to have a safe home for the winter.

It is also important to plant your pollinator garden away from areas that will be treated with pesticides and away from public walkways. Some people are allergic to or afraid of bees or consider flies and wasps to be a nuisance. If your garden is in the front of your house, you might want to plant your best pollinating plants toward the back of the bed. A strategically placed shrub or tree is another way of protecting pollinators.

 A cluster of orange coneflowers allows butterflies and birds access to abundant nectar and seeds without excessive movement or exposure to predators. The shrub in the back offers protection. (Image credit: NC State Extension, Chris Moorman)

Diversity/Seasonality

A garden made of different types of plants (especially if they are native) is the best type of pollinator garden. Native plants are best because pollinators and native plants have evolved together. The NC Wildflower Association has developed an excellent chart of native plants that includes sun requirements and seasonality. The NC State Extension office provides a list of pollinator plants that include trees, shrubs and vines. These are useful tools in developing a garden that will valued by pollinators all year round.

As you begin your landscape design, be sure to think vertically as well as horizontally. Dr. Carley cautions that you need layers for depth and smooth transitions between plant layers. Thin clumps (or sweeps) of perennials that bloom early in the season that are planted close to other perennials that bloom later means that you have diversity as well as seasonality. It also makes your garden look better because something is always blooming.

To get some height consider a tree. One of the best is the Eastern Redbud (Cercis canadensis). It is one of the few plants that has flowers before leaves. It blooms in early spring when pollen from other plants is scarce and it has high quality pollen and nectar. Honey bees, bumble bees, mason bees, cuckoo bees, long-horned bees, mining bees, and sweat bees love it. Redbuds are also a host plant for the larvae of several butterflies and moths. Songbirds and some other mammals eat the seeds. What’s not to like?

Pair the Redbud with shorter shrubs such as a native Sweetbush (Clethra alnifolia) which blooms much later but is visited by hummingbirds, butterflies, native bees, and later by birds who enjoy the fruit and a few shorter plants like the Cardinal Flower (Lobelia sp). Maybe even a few annuals for filling those bare spaces? Now you have a garden that is on the A-List for pollinators but is also attractive to look at.

Eastern redbud (top left) is one of the first plants to flower in the spring, and cardinal flower (right) and goldenrod (bottom left) are two excellent late-season nectar sources for bees, butterflies and other insects. (Image credit: NC Cooperative Extension, left photo by Alice B. Russell; other photos by Chris Moorman)

As a final thought, I quote Dr. Carley “there is no garden too small or landscape too large to include pollinator habitat. Together we can help protect our pollinator friends, and maybe we can inspire others along the way”.1

Note1: If you are interested in getting Dr Carley’s book, it is available through UNC Press.

Additional Reading and Resources

To learn how you can foster a home for bees during the winter consider leaving these plants with pithy stems during the winter. If you need to cut them, leave the long stems until spring in an obscure place in your landscape: https://content.ces.ncsu.edu/how-to-manage-a-successful-bee-hotel/appendix-3-plants-that-produce-hollow-or-pithy-twigs-and-stems-used-by-nesting-bees

Here are some suggestions on specific plant that will attract pollinators to your garden:

https://content.ces.ncsu.edu/landscaping-for-wildlife-with-native-plants

https://gardening.ces.ncsu.edu/attracting-birds-beneficial-insects-other-wildlife/pollinators-and-other-beneficial-insects

The North Carolina Arboretum provides suggestions for plants and landscaping for a home pollinator garden: https://www.ncarboretum.org/2020/05/08/ask-the-arboretum-creating-a-pollinator-paradise-garden/

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From Beloved to Invasive: How does it happen?

On By durhammastergardenersIn benign non-native plant, bird friendly habitat, bugleweed, conservation, crape myrtle, Durham NC, ecological sustanability, ecology, gardening, Gardening information, gardening NC, heavenly bamboo, hellebore, how plants become invasive, Invasive Atlas of the United States, invasive plants, Japanese stiltgrass, lenten rose, lesser threat invasive plant list, liriope, monkey grass, nandina, native ecology, native ecologynative plant ecology, native plants, Natives, NC biodiversity, NC conservation, NC Native Plants, New Hope Bird Alliance, non-native plants, ox-eye daisy, perennials, polyculture, privet, protecting native plants, Rose of Sharon, Russian olive shrub, sustainable garden design, sustainable gardening, sustanability, Uncategorized, urban garden, urban gardening, watch list for invasive plants

By Jeannie Arnts , North Carolina Extension Master GardenerSM volunteer of Durham County

I have volunteered as a recorder for the New Hope Bird Alliance (formerly Audubon) Bird Friendly Habitat (BFH) team since 2018. The BFH team, consisting of a plant expert and a recorder, visits homeowners’ yards to identify native and invasive plants and make recommendations for improvements to achieve an ecologically beneficial habitat for birds, insects, and other wildlife. Since I have joined the group, plants previously recognized as non-native, non-invasive plants have been moved onto the “Watch List” or “Lesser Threat Invasive” list. Other plants previously considered lower threat have been moved to a higher threat category. The question arises, “What is it that changes a benign non-native into an invasive?

When is a Plant Determined to be Invasive?

Plants are categorized as invasive once they disrupt the ecology of intact, functioning eco-systems, leading to loss of biodiversity and habitat degradation. This results in huge economic damage valued in the billions of dollars to agriculture, forestry, and personal property. Invasive plants compete with our natives for critical and often limited resources like sunlight, water, nutrients, soil, and space. Anyone who has ridden the train at the Museum of Life and Science in Durham and seen the Russian olive shrubs (Elaeagnus sp) overtaking the landscape along the tracks or been on a hiking trail in many Triangle forests and seen the stiltgrass (Microstegium vimineum) engulfing the entire ground cover of the forest floor can easily see the impact of invasive species.

Russian olive shrubs (left) out-compete native plants and dominate riparian areas primarily in central and western USA. Japanese stiltgrass (right) was accidentally introduced into Tennessee around 1919 as a result of being used as packing material for porcelain from China.  it has invaded many woodlands in North Carolina. (Image credit: NC State Cooperative Extension)

What Factors Influence a Plant to Become Invasive?

Biologists have been “vexed for decades” by the question of what causes some plants, once thought to be benign, non-invasive exotics, to become a risk to our eco-systems due to their invasive characteristics. The ecologist, Charles Elton, wrote the book, The Ecology of Invasions by Plants and Animals, in 1958 and, more than 100 years earlier, Charles Darwin pondered this question during his voyage on the Beagle (1831-1836). Johnny Randall, former Director of Conservation Programs at the NC Botanical Garden, noted that one reason plants become invasive is that in their new environment, they no longer have natural controls, such as pests, pathogens, and herbivores. This gives them an advantage over native plants that have been part of a region’s ecology for millennia; consequently, the invasives often out compete the natives.1

In addition, a plant’s propensity to become invasive is a function of the plant’s own biology, including a relatively short generational period, large seed production, its ability to reproduce asexually (without the need for fertilization), and having large fleshy fruits, such as those produced by Autumn or Russian olive trees (Elaeagnus sp), privet (Ligustrum sp.) and heavenly bamboo (Nandina sp.) With this latter trait, birds will eat the berries and deposit the seeds far from the original location of the plant.

A non-native, is especially prone to invasion when it sets its roots in a “matched habitat” similar from which it came, i.e., their native ranges tend to have similar temperature extremes, precipitation levels, and seasonal cycles. Stiltgrass (Microstegium vimineum) is an example of a plant that meets most of the criteria for becoming invasive. It is an annual that produces up to 1000 seeds per year, has no natural controls, reproduces asexually, and its seeds are distributed by the wind. In addition, the seed bank may take up to five years to germinate. Many gardeners who think they have eliminated stiltgrass on their property one year are befuddled to find a number of plants from the seed bank sprouting the next summer. The good news is that if you continue to manage the stiltgrass, you will have fewer plants each year.

Beloved Plants that Become Invasive

I think we can all agree that we want stiltgrass eliminated from our property, but there are non-native plants that have been beloved by gardeners for generations that are being added to the invasive lists, much to the consternation of gardeners. One example is the lenten rose (Helleborus orientalis).

Some hellebores  have started to escape into woodland areas and are able to stifle our favorite native understory flowers. They prevent seedlings of other plants from getting established as dense mats of their offspring grow. (Image credit: NC Extension Toolbox, Bob Gutowski CC-BY-NC-SA-2.0; Jim Robbins CC-BY-NC-4.0).

There are many good reasons that hellebores are such a beloved plant: they bloom over the winter months when very few other plants are blooming; they require little care; they are deer and rabbit resistant; they tolerate a wide range of light conditions; including light shade; and they survive even deep frosts. Unfortunately, they meet many of the conditions that place them at risk to become invasive in our region: they have no natural pests or pathogens; they can successfully fertilize themselves (although bees will seek nectar and pollen from the plants); and they produce a multitude of fertile seeds. While there is not a perfect native substitute for hellebores, the gardener may consider planting a matrix of sedges (Carex species), coral bells (Heuchera americana), and ferns, many of which are host plants, to provide winter interest .

While not yet on the invasive lists in N.C, another beloved plant that is of concern is the crape myrtle (Lagerstroemai indica). Its spread is being tracked in Southern states by the Invasive Atlas of the United States and the plant’s spread is being watched with caution by conservationists in N.C. Each flower of the crape myrtle produces a prodigious number of seeds that are carried or blown far from the mother plant. I have had a crape myrtle in my yard for probably the past 40 years and it has only been recently that I have seen it sprouting up elsewhere in my yard and ¼ acre woods.


Crape myrtles are seen along roadways and in gardens in North Carolina but conservationists have raised concerns because it outcompetes many native plants (Image credit: NC Plant Toolbox, skdavidson)

Liriope (Liriope muscari and L. spicata), bugleweed (Ajuga reptens), Rose of Sharon (Hibiscus syriacus), and ox-eye daisy (Leucanthemum vulgare) are all common ornamental plants that have been added to the NC Invasive Plant list as “Low Threat” species. While they have the potential to harm our local ecology, they are not yet doing so.

Liriope (Liriope muscari), bugleweed (Ajuga reptens), Rose of Sharon (Hibiscus syriacus), and ox-eye daisy (Leucanthemum vulgare) are plants that many of us have in our garden. They are considered to be “Low Threat” to native plants of North Carolina. (Image credit: North Carolina Toobox, Manuel-CC-BY-2.0; Jim Robbins-CC-BY-NC-ND; Frank Mayfield, CC-BY-SA-2.0)

As gardeners, we can control the spread of potentially invasive plants in our own yards or we can choose to remove them and plant a native that supports our native ecology. A follow-up blog will suggest options to consider for replacing invasive plants with natives that power our ecosystems.

Notes

  1. Personal communications Peter Schubert, NC Invasive Plant Council, October, 2024 and Johnny Randall, former Director of Conservation Programs, NC Botanical Garden, October 2024.

Resources and Additional Information

NC Invasive Plants List adopted by NC-IPC, November 16, 2023NC Invasive Plant Council
https://nc-ipc.weebly.com/uploads/6/8/4/6/6846349/invasive_plant_list_-_ranked_-_2023-11-16.pdf

Grzędzicka, E., Assessment of Habitat Selection by Invasive Plants and Conditions with the Best Performance of Invasiveness Traits, February, 2023. https://www.mdpi.com/1424-2818/15/3/333

Invasive plant Atlas of the United States University of Georgia-Center for Invasive Species and Ecological Health, October 2018 https://www.invasiveplantatlas.org/index.cfm

Jones, M., Gaster, R. Invasive Species, NC Cooperative Extension, Lee County, July 30, 2019 https://lee.ces.ncsu.edu/2019/07/invasive-species/

Moony, H.A., Cleland, E.E., The Evolutionary Impact of Invasive Species, Proceedings of the National Academy of Sciences. May 2001, 98(10) 5446-5451 https://www.pnas.org/doi/full/10.1073/pnas.091093398

Moorman, C, Megalos, M, Douglas, K. Invasive Plants and Your Forests, NCSU Extension Publication. Revised September 11, 2024. https://content.ces.ncsu.edu/invasive-plants-and-your-forests

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