From Beloved to Invasive: How does it happen?

On December 11, 2024July 5, 2025 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 Gardener^SM 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

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

Article Short Link: https://wp.me/p2nIr1-5l3

Leave The Leaves: A Simple Way to Help Wildlife and Your Garden

On October 23, 2024October 23, 2024 By durhammastergardenersIn bees, beneficial insects, composting, dealing with fall leaves on lawn, Durham NC, fall gardening, garden design, gardening, Gardening information, gardening NC, insects, lawns, leaves, mulch, pollinator gardening, pollinators, soil, soil health, soil microbes, sustainability, sustainable gardening, sustanability, urban wildlife

By Marcia Kirinus, NC State Extension Master Gardener^SMvolunteer of Durham County

Did you know that the National Wildlife Federation has designated October as Leave the Leaves Month? This initiative encourages people to rethink traditional fall yard clean-up by leaving fallen leaves in place—or at least on your property—instead of bagging them up and sending them to the landfill

Traditional fall clean-up often involves raking or blowing leaves, bagging them, and setting them out on the curb. Then we head over to the big box store to buy mulch and fertilizer to replace what nature is already providing. This process is time consuming, resource draining, and unnecessary. Leaves are not trash. We are missing an opportunity.

Instead, let nature do the hard work — your garden will thank you. The thing that is most natural to do — the thing that happens in nature — is to let your leaves lie where they fall. If you have extra leaves, bag them and offer them to neighbors or local gardeners who can make good use of them.

Beyond convenience, there are significant benefits to leaving the leaves. First and foremost, they nourish the soil. As leaves decompose, they enrich the soil with nutrients, promoting healthier, richer soils. Consider them free mulch and fertilizer. Second, leaves insulate the soil, protecting it from temperature fluctuations. They also help retain moisture. Finally, leaves make incredibly important habitats for wildlife. Have you noticed a decline in lightning bugs? Most of their life cycle is spent under leaf debris. By keeping your leaves in place you can boost wildlife habitats, enrich your soil, and even help with global environmental challenges.

Left: Adult Firefly. Right: Larvae of Firefly . Most fireflies are habitat specialists. They rely on undisturbed leaf litter for one year or more to complete their lifecycles. These insects spend most of their lives as larvae preying on earthworms and other animals in the soil or leaf litter. If that habitat is disrupted during their youth, populations can be extinguished. (Image credit M. Bertone, NCSU Entomology.)

Last year’s oak leaves slowly decomposing with the help of small pinwheel mushrooms (Marasmius rotula). Image credit: Jean Epiphan

Soil Enrichment: The Cornerstone of Healthy Gardens

Soils rich in organic matter absorb and retain water better, turning a soggy lawn into a sponge-like garden bed. In as little as two years, you can turn those wet areas into walkable spaces. It’s not a miracle as building soils naturally is a slow process, but it’s a start and it’s free.

Healthy soil, enriched by decomposed leaves, supports deep-rooted plants, reduces watering needs, and improves plant resilience.

Wildlife Benefits: From Moths to Bumblebees

Leaves provide shelter for many species, including fireflies, butterflies, Moths and endangered bumblebees. Caterpillars overwinter in leaf litter, which also sustains backyard birds in spring. By leaving leaves on the ground, you’re creating essential habitats for these creatures, helping maintain biodiversity and supporting the larger food chain, from insects to birds. Caterpillars, which overwinter in the leaf litter, are a primary food source for 96% of backyard birds during the spring.

From Left to Right: Luna moth pupae, ( Actias luna ), are often difficult to see as they are a chestnut brown and overwinter in leaf litter. In the spring it will emerge as a soft green, 3 to 4.5 inch moth. All life stages provide food for predators. (Image credit: Donald W. Hall, UF) Leaf litter is the ideal Earthworm habitat. Earthworms provide beneficial castings which are building blocks to healthy soil. (Image credit: M. Bertone, NCSU) Woolly bear (Pyrrharctia isabella) construct shelters like this one made from pine needles to protect themselves from the winter elements. They also commonly use leaf litter and other yard debris. (Image credit: batwrangler, flickr. with permission)

Small Acts, Big Impact: Helping with Global Change

By making small changes in how we manage our yards, we can create big environmental benefits—both locally and globally. Leaving the leaves isn’t just about benefiting your yard—it’s about making a difference on a global scale. Encouraging wildlife and helping to maintain a balance in the food chain is one way you are helping. By skipping the blower and rake, you also reduce fossil fuel consumption, lowering your carbon footprint. Additionally, leaves that are sent to landfills contribute to methane emissions as they decompose without oxygen. Composting them in your yard helps reduce these emissions.

If you still want to move your leaves around the yard, consider using a rake instead of a blower. Rakes are quieter, healthier for you, and don’t rely on fossil fuels. They also give you more control, allowing you to gently move the leaves without disturbing the soil or nearby wildlife. My neighbor for 17 years told me that he can rake faster than he can blow his leaves. I was dubious. At the time, my clean-up tool was a blower. However, I hated the noise and smell so I took his words as a challenge. I pulled out the rake and never looked back. I can rake faster, and with a lighter touch. I can listen to the birds and I feel stronger, fitter for doing so.

I also reduced my turfgrass lawn significantly so I can leave the leaves in place. I converted it into valuable wildlife habitat by planting native ferns and flowers. Lawns require water, fertilizer, and herbicides, not to mention mowing, which creates noise and uses fossil fuels. And lawns are wildlife dead zones. However, I still need a place to play fetch with Moira, so a small patch of “meadow” remains. I say meadow because it is green – mostly clover.

Making the most of your leaves

Here are a few simple strategies to keep them working for you. You don’t have to leave all the leaves exactly where they fall.

On Lawns: A thick layer of leaves can suffocate your lawn. Instead, run a mower over the leaves to chop them into smaller pieces. A thin layer (1–2 inches) of shredded leaves can actually nourish the grass over the winter, breaking down over time to feed the soil.
Flower or Vegetable Beds: Spread whole leaves in flower beds or vegetable gardens. They act as mulch, suppressing weeds and adding organic matter as they decompose, improving soil structure and fertility. For most garden beds, a leaf layer of 3–5 inches deep is ideal. Avoid piling leaves directly on top of plants; instead, place them around the plants, covering any exposed soil. This will suppress weeds, preserve soil moisture, and return nutrients to the roots as the leaves decompose.
Composting: Leaves are perfect for composting—rich in carbon and ideal for building fertile soil. Consider adding them to your compost pile or creating a leaf mold. If the wind blows leaves into unwanted areas, let nature guide them into natural piles, and then redistribute the leaves to your garden beds or around trees.

From left to right: Mower cutting leaves into small pieces instead of removing them (Image credit: Pixaby);. Moving whole leaves to help create paths by suppressing weeds (Image credit: Justin Butts). Composting excessive leaves (Image credit: Christy Bredenkamp, NC Extension Director, Moore County).

Conclusion: A Small Change with a Big Impact

With just a few thoughtful changes, as gardeners and homeowners, we have the power to make a positive impact on the environment by simply rethinking how we take care of our little piece of earth outside of our back door. This October, join the movement and Leave the Leaves—because every leaf left behind makes a difference.