Category: urban garden

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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Mustard: It’s Not Just for Hotdogs

On By durhammastergardenersIn adding vegetables to annual flowers, annuals, bees, beneficial insects, container gardening, Durham NC, easy to grow plants, edibles, fall gardening, fall vegetable gardening, garden design, gardening, gardening in pots, Gardening information, gardening NC, growing mustard, landscaping for wildlife, mizuna, mustard plants, pollinator gardening, pollinators, sustainability, Uncategorized, urban garden, urban gardening, vegetable gardening

By Melinda Heigel, NC State Extension Master GardenerSM volunteer of Durham County

(Left) The big, bold leaves of ‘Red Giant‘ mustard take center stage in this large container providing texture, height, volume, and intense color. This mustard was fast growing, survived cold temperatures with minimal protection. It was also slow to bolt when the weather got warm in the spring. (Middle and right) The ‘Miz America’ mizuna-mustard hybrid was equally stunning in a built-in planter box and potted alongside pansies, violas, and a lemon cypress, (Hesperocyparis macrocarpa ‘Goldcrest’ ). While these head turners are edible, I planted them for their color and form. (Image credit: Melinda Heigel)1

Wait? I thought this was a blog about gardening, not cooking! Well, the mustard I am referring to isn’t the zippy condiment we all know but is the plant I discovered is a star in fall containers. I’ve written in the past about the herb bloody dock, also known as sorrel, and what a bullet-proof companion it is for pansies, violas, snapdragons, ornamental kale, cabbage, and other autumn-to-spring plants. Last year I tried adding mustard to my potted arrangements and was thrilled with the results.

A Question of Hardiness

Along with broccoli, collards, and kale, mustard is a cole crop that performs best in consistently cool temperatures when grown in the vegetable garden. But over the last couple of years I’ve started seeing different mustard plants at the local nurseries more and more alongside the annual cold-weather ornamentals. The mustard plants offered some really interesting leafy forms for planting in pots. I was dubious, though, about their hardiness over the winter, unprotected in containers, but what is gardening without experimentation? With the exception of a couple nights with temps in the teens in the dead of winter, I did not cover any mustard plants. To my surprise, they performed just as well as their cool-weather container companions.

(Left to right) Mustard plants already making a debut at the local nursery this month alongside fall’s usual suspects. In late spring of 2024, my ‘Miz America’ mustard plants produced bright yellow flowers when they bolted. The plants really earned their keep–providing interesting leaves for months followed by these showy late-spring blooms. And did I mention spring pollinators were drawn to their nectar and pollen? (Image credit: Melinda Heigel)

If the spring weather warmed up too quickly, as it is known to do in central NC, I also wondered whether these cool-temp lovers would bolt (flower) and fade too quickly given their prominent placements. Most of the containers were in the hottest place around our house–on a dark-colored deck that receives full sun. Happily, the mustard tolerated a good number of hot days in late April and early May before bolting. Even after flowering, they were still going strong when I removed them to make way for summer plants. While I may have just the right conditions in my landscape for these results, I can’t chalk this success up to anything remarkable. Mustard plants are easy to grow. And I’ve come to find out, one of the types I planted is actually bred to be bolt resistant, ensuring longevity.

Mustard Varieties for Annual Container Gardening

Red Giant Mustard (Brassica juncea ‘Red Giant’)

I found this to be a striking specimen. In my big container, it quickly grew to be over 3 feet tall, with gracefully arching leaves that reminded me of a classical acanthus—yes, you really can wax poetic about mustard. If grown in optimum conditions, this plant has been reported to grow as large as 4 feet. Though I have not experienced this, don’t underestimate its vigor. When planning your mixed pot, give it plenty of room. ‘Big Giant’ mustard leaves start off green but mature into a deep maroon with contrasting green stems, midribs, and leaf veins. This plant is specifically bred to be both cold-and-bolt tolerant. Frost intensifies the color. It grows best in full sun with well-drained soil. It paired nicely with the flowering cushion spurge ‘Ascot Rainbow’ (Euphorbia x martinii ‘Ascot Rainbow’) as a backdrop.

In terms of its characteristics as an edible, this mustard has a bold taste like wasabi or horseradish and can be pickled, eaten cooked (mature leaves), and eaten raw (young leaves). Hot weather sharpens the flavor, especially in the older leaves of the plant.

‘Red Giant’
‘Miz America’

Image credit: Melinda Heigel

Miz America Hybrid (Brassica juncea ‘Miz America’)

At once striking and delicate, the deeply lobed and serrated leaves of this mustard are a showy deep burgundy with vibrant hot-pink midribs and venation. Like ‘Red Giant,’ it is a fast grower and prefers full sun. It serves as an excellent filler in containers, given its upright and compact habit.

From a culinary perspective, ‘Miz America’ has a mild peppery flavor. It’s a hybrid plant that comes from crossing two distinct mustard varieties. One of the parents, mizuna, is a mild green mustard, which gives ‘Miz America’ its beautiful serrated edges and mild flavor. You can enjoy the leaves of all mustards in a salad by picking them young—under 6 inches. If picked at a more mature size, they can be added to a dish to impart a hint of sweetness with a mustard tang. Consider adding them to a bowl of hot, creamy soup such as butternut squash or tomato. Not only does it give you additional nutritional value without adding additional calories, but it adds a nice crunch and a bit of zing.

I’ve yet to replant my containers and built-in planter box this fall, but you’d better bet that mustard plants will be making a repeat performance in 2024. I’ve already seen ‘Red Giant’ in the nurseries, but I am also on the hunt for some other intriguing mustards to test out—namely ‘Brazen Brass’ and ‘Dragon Tongue.’ If you want something unusual, showy, and even tasty in your fall plantings, remember to go heavy on the mustard.

Notes

1–Want a closer look at a photo? Simply double click on the image for a better view.

2–According to Missouri Botanical Garden, Brassica juncea, known by its common names Chinese mustard or brown mustard, is listed as a noxious weed in some states including Michigan, Florida, and Alaska and considered invasive. Cultivars discussed here are bred to be used as annual edibles or ornamentals in gardens.

Resources and Additional Information

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