invasive

When Banning an Invasive Plant Is Bad

Now that the election is past, there is a shortage of contentious discussion, so it seems like a good time to mention a horticulture battle: native plants versus non-native plants. There are rabid supporters in both camps, both with rational arguments.

One of the reasons that this topic moved to the top of my blog priority list is the recent ban on the sale of Elaeagnus, a shrub whose common names include Silver Leaf, Thorny Olive, Silverthorn, Autumn Olive, and Russian Olive (and Ugly Agnes among its detractors). Beginning October 1, 2024, South Carolina banned the sale of Elaeagnus angustifolia, Elaeagnus pungens, and Elaeagnus umbellata. This makes it the second genus with sales banned in SC, after Bradford Pear.

I do not dispute the downsides of growing Autumn Olive in the garden. Birds eat the seeds and spread them into forests and woodlands, where they may displace native shrubs. They can fix nitrogen in poor soils and establish themselves as a monoculture, never a healthy situation. Left unrestrained, they can throw rampant growth and shade out native plants. All negatives, certainly. But in banning all these Elaeagnus, we are ignoring the research and development of non-seeding cultivars underway in a neighboring state. And we are turning a blind eye to Autumn Olive’s ability to stabilize steep slopes with poor soil, where few natives would survive. Demonizing the entire genus makes as much sense as banning ALL Butterfly Bush or Rose of Sharon, even though there are sterile or seedless cultivars available.

There are those who encourage the ban of Nandina. While Nandina berries are toxic to birds that gobble too many of them, there are few other heat- and drought-tolerant plants that will thrive in sun or shade, any soil texture or pH, with no added irrigation. Banning the sale of Nandina ignores the multitude of non-invasive or seedless cultivars: ‘Gulf Stream,’ ‘Flirt,’ ‘Fire Power,’ and ‘Harbour Dwarf,’ to name a few.

Not all natives are innocent. Trumpet Vine (Campsis), Goldenrod (Solidago ), Cattail (Typha latifolia), and Fishpole Bamboo (Phyllostachus aurea) spread like mad and can choke out other valuable plants. Some of our most beautiful plants are not native. I am not willing to remove my Camellias (both C. japonica and C. sasanqua), Bigleaf Mophead Hydrangeas, or Encore™ Azaleas. None of these are native to the United States.

Often, plants that are invasive in one part of the country are fine in another. I was surprised to find Castor Bean (Ricinus communis), Chaste Tree (Vitex agnus-castus), Pachysandra (Pachysandra terminalis), Mock Orange (Philadelphus coronarius), Creeping Jenny (Lysimachia nummularia), and Thunberg Spirea (Spiraea thunbergia) on the Invasive Plant Atlas of the MidSouth, published by the US Geological Survey. To download a complete list, click HERE. I have never experienced an out-of-control spread of any of these. In the case of Pachysandra, I had to plead with the plant to survive and spread.

To quote politicians’ jibber-jabber ad nauseum, “let’s work both sides of the aisle” to make wise choices for our specific areas. Beautiful gardens can contain a mixture of both natives and non-natives. Just make thoughtful selections. There are good choices and bad choices but no inherently evil plants (except for Chameleon Plant, Houttuynia cordata – straight from Hades).

The leaf underside of Elaeagnus pungens. Photo by Bri Weldon used under CC BY 2.0 license.

Tree of Heaven (NOT)

Look out, Bradford Pear tree. There is a new contender for the title of Worst Invasive Tree in the US. It is Tree of Heaven, Ailanthus altissima. Tree of Heaven (TOH) was introduced by a Pennsylvania gardener in 1784 as an ornamental. Native to China, it has spread like mad and is now found in 42 of the lower 48 states. TOH tolerates any type of soil, any moisture level, and any soil acidity. It grows in sun or shade. It produces hundreds of thousands of seeds annually. Within three months of seed germination, the tree has put down a taproot that helps it survive drought. It grows fast, up to heights of 80 feet, although 30 feet is more common. TOH has escaped cultivation and is displacing native trees in both urban and rural locations, the definition of invasive. Its roots damage plumbing pipes AND it serves as a host plant for the damaging spotted lanternfly. For additional information from NC State University, click HERE.

TOH leaves resemble sumac or black walnut leaves, with 10-40 leaflets arranged along a central stem that may reach up to four feet. Like black walnut (Juglans nigra), TOH exudes toxins that stunt surrounding plants that compete for moisture and nutrients. When crushed, the leaves smell bad. TOH flowers in middle to late summer, usually July to August. Flowers produce seeds in papery envelopes called samaras. Think of a maple tree’s helicopter seeds that have been pinched in the middle and you have a pretty accurate picture of what TOH seeds look like.

Not only does TOH spread with a vengeance, it is extremely difficult to control. It spreads by seeds and by root suckering — Little Shop of Horrors, indeed. Note: If you are opposed to herbicide use, stop reading now. Research is ongoing for biologic controls. If you merely cut down a tree without applying herbicide to the fresh cut, babies emerge from all the surrounding roots as well as from the trunk. If you try to remove a tree with machinery, any tiny portion of root left behind will spring into life as a new tree.
There are several recommendations for control. These methods include applications of herbicides glyphosate or triclopyr, and a satisfying-sounding method known as “hack-and-squirt.” Click HERE for detained instructions from the NC Forest Service. Remember to follow application instructions exactly. “The label is the law.”

Be aware of what is growing in and around your property. Any unwelcome invader is easiest removed when young. Eliminating the preferred food source will help control invasive spotted lanternfly. TOH control might save your plumbing, your driveway, and your surrounding woodlands. A widespread effort can prevent Tree Of Heaven from becoming the next kudzu or Bradford Pear.

Queen Anne's Lace

When a plant’s common name includes “weed” many people are hesitant to introduce them into a cultivated garden. But those same weeds can prove to be resilient, hardy, and attractive. Consider Butterfly Weed (Asclepias) or Iron Weed (Vernonia) as two examples. The downside of growing weeds is the possibility that they can be TOO resilient, even bordering on invasive. That is the case with today’s featured plant, Queen Anne’s Lace.

Queen Anne’s Lace (Daucus carota, pronounced DAW-kus kar-OH-tah) has a fat, carrot-like tap root that helps it survive in hot, dry climates. It is quick to spring up in disturbed areas, and is listed as invasive in more than 20 states. Queen Anne’s Lace, also called Wild Carrot, Bee’s Nest or Devil’s Plague, is a biennial. It develops lacy basal foliage in its first year, then blooms second year. Mature plants range from 2-4 feet, with a narrow footprint. It is found in all the lower 48 states, in full sun to part shade.

Queen Anne’s Lace flowers are flat white umbrels up to four inches across with one little purple flower dot in the middle. If you place cut flowers’ stems in colored water (use a few drops of the same vegetable-based colors used in cake icing), the blooms rapidly take up the dye and will change from white to a pastel shade of the selected color. I thought every child had done this at least once, but it appears I was mistaken.

Spent flower heads curl up on the edges into a brown cup-like form that resembles a bird’s nest. They become brittle when dry. Winds break them off their stems, and they tumble about, spreading seeds far and wide. This promiscuous habit, along with their tolerance for any type soil and any pH, means that they spread everywhere unless consistently deadheaded. Cut stems stink but the smell wanes fast enough to enjoy them as cut flowers. I once had to resort to herbicide to rid a perennial bed of these, and have since decided to just enjoy them along roadsides. They are prolific in my area of the southeast. Bees and butterflies love the flowers, and swallowtail butterfly caterpillars eat the foliage.

Parts of the plants can be cooked and eaten in small quantities, but larger amounts are toxic. Contact with leaves and stems can cause dermatitis. Unless one in starving in the wilderness, I see to need to test out the toxicity threshold. If you feel the need to consume, be positive of your plant identification. Queen Anne’s Lace is easily confused with Wild Parsnip and Wild Hemlock. Consuming either of these can be deadly. Wild Hemlock is the plant that killed Socrates. Its stem has purple spots.

Cluster of tiny white flowers into a single umbrell

Note the single purple flower in the middle. Not every umbrell has this oddity.

A single plant, flowering in an undeveloped roadside.

A community of Queen Anne’s Lace shows how the plant can multiply into large communities.

Mahonia

“The dead of winter.” That phase accurately describes the Mary Snoddy garden right now. My dormant mostly-Bermuda lawn is the color of a manila file folder.  The flower beds look forlorn. Amid all this dreariness, the lemon yellow blooms of Mahonia bealei glow like a beacon in the winter landscape.

The common Mahonia (pronounced mah-HOE-nee-uh BEEL-lee-eye) originally hails from China, but has spread itself across the southeast in damp, shady areas. This shrub has thick, leathery leaves (common name is Leatherleaf Mahonia) shaped like giant holly leaves, complete with sharp points. Should you injure the bark either through accident or pruning, you will find the underlying tissue is a bright yellow, just like its distant cousin, the barberry. It is evergreen, but a few leaves may turn red or orange and drop in autumn.

The plant is not included in the List of Invasive Plant Pest Species compiled and revised in 2014 by the South Carolina Exotic Pest Plant Council, but NC State University includes it in their Invasive Exotic Plants of the Southeast, and recommends control via a combination of fruit removal, drastic pruning, herbicide, and root ball removal. I take this to mean that they feel the shrub should be removed entirely.  Invasive.org indicates that this tough customer is on the bad list in South Carolina, Alabama, Tennessee and Georgia.

One does not need a horticulture degree to realize that this hardy specimen has invasive tendencies. The fragrant blooms are followed by clusters of green berries that mature to an attractive blue-purple shade, often with a powdery dusting described by botanists as “glaucous.” The berries are favored by birds. I suggest that you avoid line-drying any laundry during the 2-3 weeks that ripe berries are present (unless, of course, you prefer your clothing and bed linens with random purple stains). Any berries not removed by birds fall to the ground, where they germinate readily. I do a twice-yearly hoeing to remove all these unwanted seedlings. Otherwise, a thicket would develop.

Mature shrubs will grow 5-10 feet tall, with a 4 foot spread. They have a tendency to become lanky, with bare lower stems, similar to species Nandina. Counteract this by pruning a few of the leggy stems each year down to a height of six inches. It looks drastic, but they will throw new growth at the cuts and look much better.

There are some newer introductions of Mahonia that may be less invasive. ‘Winter Sun’ is beautiful and fragrant. On winter days with temperatures above 50 degrees, the honeybees swarm around the sweet blooms. Introduced in 2006, Mahonia eurybracteata ‘Soft Caress’ grows in the same damp shade as its cousin, but the foliage is soft and finely cut, resembling bamboo.  It is smaller (3 feet, maybe) and perfect for an Asian garden. It has the same yellow flowers, but mine bloom in September/October rather than January/February like the Leatherleaf.  Mahonias put down some deep roots, which means that mature specimens are somewhat drought tolerant (yay) but difficult to relocate or remove (boo). All Mahonias are deer resistant.

Photos: Left - ‘Winter Sun’; Middle - The beginnings of an invasive thicket; Right - ‘Soft Caress’