Invasive plants have a way of stealing the spotlight from island-native showstoppers in the early spring. As many of our native plants prepare to unfurl new leaves, Norway maple (Acer platanoides) foliage already casts a shadow below, and lesser celandine (Ficaria verna) carpets the ground with bright yellow flowers. Friends may even gesture to new growth on Japanese barberry (Berberis thunbergii) as if it’s the pinnacle of spring beauty.
Admiring signs of spring can become complicated when you start to recognize invasive plants. Sometimes I will even catch myself excitedly running up to a sole green leaf just to realize it’s coming from an autumn olive (Elaeagnus umbellata). I’ve learned to view this otherwise overwhelming realization as an opportunity.
Many invasive plants are most vulnerable to mechanical removal when they’re using energy to produce new growth. In this weakened state, their braggadocious early leaf-out can help flag them for prompt removal. Repeatedly applying stress during this time when they’re focused on pushing out foliage and flowers can exhaust their root systems and erode plant health over time.
Of course there is also an advantage to catching new growth while it is still small and manageable. Pulling a burning bush (Euonymus alatus) seedling is a lot easier than digging away at a mature shrub. Any time you can stop a young plant in its tracks helps avoid a harder job in the future.
Starting on invasive plant management early can save you time and some sanity. To help you take action against early emerging invaders, I’ve put together a list of early growth from some of our most common invasive species that you should look out for.
Japanese Knotweed (Reynoutria japonica)
Right now Japanese knotweed infestations look like groves of dried woody stems. Although the winter brings dormancy above ground, the plant is still very much alive. Rhizomes transported during the winter can lead to other infestations in the spring. Soon, new growth will start to poke through the soil and replace the hollow remains from last season.
Keep a close eye on knotweed patches as they begin to send up new canes in the early spring. Young growth can range in color from red, to purple, to green. These small unassuming sprouts can grow to full size in less than a month.
To manually manage knotweeds, conduct at least three cuttings throughout the growing season and either bag all of the debris or leave it on-site on a tarp or other impervious surface so it cannot re-root. For the biggest impact, start with a cutting as knotweed first leafs out and then trim back new growth every several weeks. Repeat each growing season for two or three years and monitor the area.
Knotweeds reproduce vegetatively and can grow new plants from small fragments. Take extra care not to spread plant matter or rhizomes when managing this plant.
Round-leaf Bittersweet (Celastrus orbiculatus)
It is no secret that bittersweet is a huge problem on the island. This pesky vine is the Invasive Plant Brigade’s most frequently encountered invasive plant at removal sessions. New leaves and seedlings start to emerge as early as April.
Young plants have bright green alternate leaves with rounded serrated edges and are usually numerous in established infestation sites. First-year seedlings can be pulled from the ground rather easily, whereas offshoots from established root systems may look like seedlings but will be much harder to remove.
Pull seedlings when possible starting in the early spring and cut large vines and any re-growth low to the ground throughout the season. Be sure to conduct a cutting in July or August just before fruits develop to avoid spreading seed. Dig out root systems when possible, but take extra care to remove all of the roots as new growth can establish from small fragments.
As with all invasive plants, persistence is key. Repeated cuttings will prevent the plant from photosynthesizing and exhaust the root system over time. For the best results, repeat this process annually throughout the growing season.
Thunberg’s (or Japanese) Barberry (Berberis thunbergii)
Barberry can be a real pain! Luckily this thorny shrub has distinctive foliage even as a seedling, which can make early detection feasible. You may recognize barberry from hedgerows, where it can have red or purple leaves. When these cultivars escape into the wild, they typically revert back to their original form: green and gangly.
The leaves are small, alternate, spoon shaped, and arranged in clumps along multiple arching stems. A single sharp thorn pokes out from each node, which can make removal without leather gloves painful. Another troublesome barberry from Europe can be distinguished from Japanese barberry by its serrated leaves and spines in groupings of three at each node.
Leaf out can begin as early as March, so keep your eyes peeled and act fast. Manual removal primarily involves hand-pulling small seedlings and weed-wrenching larger bushes. Extra care should be taken to remove the entire root system which can be extensive. Revisit removal sites and continue management as needed.
Invasive Wisteria (Wisteria sinensis)
Soon wisteria gardens will be draped with purple flower clusters that win the hearts of many gardeners. What seldom warrants a similar reaction is the expansive woven root systems that creep under yards, infiltrate wild areas, and even weasel their way into houses!
Those classic violet colored flowers will bloom around the same time wisteria leaves are starting to unfurl in the early spring. The leaves are alternate and pinnately compound with 7-13 leaflets. Older vines will continue to climb up whatever their target may be, while new plants grow down below or sprout elsewhere from a previous seed dispersal.
Start by hand-pulling small seedlings when possible. Sometimes a plant can look like a first-year seedling but actually be new growth from an established root system. Roots from an old infestation are difficult to dig out and are likely to overlap with desirable vegetation that would be harmed by a large excavation project. Like all plants, wisteria may be exhausted over time with enough grit and determination.
Cut back large vines and any offshoots in April and continue cutting regrowth every two or three weeks until fall. Sadly, there are rarely one-and-dones in the invasive plant management world, so always revisit your site the next growing season and continue management as needed.
Wineberry (Rubus phoenicolasius)
I can spot wineberry from a mile away in every season. Those downy red stems stand out like flames in a forest of brown and beige. You hardly need foliage to recognize this troublesome invader, but you should leverage the vulnerability that the early growing season brings anyhow.
Heart-shaped compound leaves with toothed margins and white undersides will begin emerging as soon as early April. New growth is bright green with pronounced wrinkles, like a butterfly that has recently emerged from a chrysalis. Keep watch for young seedings and old canes with opening buds.
Wineberry can be pulled rather easily, but make sure to bring tough gloves to protect your hands from prickles. Revisit removal sites and continue pulling regrowth to deplete the population over time.
Autumn olive (Elaeagnus umbellata)
It’s rare for me to find a property that’s untouched by autumn olive. A common invader in disturbed sites, its tolerance to a variety of conditions and its opportunistic nature make it difficult to avoid. I’ve seen it along roadsides, in meadows, near wetlands, and even groomed as an ornamental.
From a distance, this invader might blend in among other woody, multi-stemmed shrubbery before its leaves unfurl. At a closer look, you’ll see silvery scales speckled along young gray stems; these can also be seen on seedlings, leaves, and fruits when they emerge.
In as few as three years, this shrub can grow to maturity and produce viable seed. In just one growing season, a single shrub can produce hundreds of thousands of seeds that are distributed by wildlife or fall to the ground on their own. Despite the jarring abundance of seed-bearing fruits, Autumn olive berries are not as nutritionally valuable as those of native shrubs.
To manually control autumn olive, hand-pull seedlings when possible and cut back mature shrubs three to six times a year. You can also tightly wrap stumps with black plastic and secure them to make sure no sunlight can reach any part of the plant. The goal is to exhaust the root system by obstructing photosynthesis, which will stop fruit production and weaken the plant over time. Repeat the next growing season as needed.
Garlic mustard (Alliaria petiolata)
Garlic mustard is usually one of the first invasive plants I start to notice in the spring. It maintains a green color late into the fall and resumes growth in the early spring.
Garlic mustard is a biennial herb. In the first year, a basal rosette forms low to the ground with kidney-shaped scalloped leaves, and in the second year a tall flowering stem grows with alternate, triangular, coarsely toothed leaves. Flower clusters appear in May with small four-petaled white flowers. Soon after flowers emerge, seed pods with 10-20 small seeds begin developing.
If you struggle with visual identification, your nose knows! Young leaves will release a garlic-like odor when crushed.
Hand-pull first- and second-year plants in the spring as they emerge. Proceed with caution as pulling creates soil disturbance which can result in additional germination. Return to the removal site throughout the growing season to continue pulling as needed.
What you can do
These are just seven early emerging invasive plants on Martha’s Vineyard, but many others will be sneaking to the surface within the coming weeks. Review the manual invasive plant removal calendar below for more information on other species.
Keep watch for green peaking through the ground in March and early April and use iNaturalist to identify what you see. Your observation will contribute data to the Martha’s Vineyard Atlas of Life, and if it ends up being an invasive plant, it will automatically be added to the Martha’s Vineyard Invasive Plant Atlas iNaturalist project.
If you want assistance removing invasive plants on your land and/or would like to help others with removals, consider joining the Invasive Plant Brigade! Spring is the perfect time to get ahead of pesky invasive plants before they grow large and set seed. Check out my other blog posts to learn more about disposing of terrestrial invasive plants and stewarding your removal site to encourage native regrowth.
Not all early emerging plants are invasive. There are several iconic island-native species that start to show themselves early in the growing season. Learn more about these native showstoppers in Natural Neighbors Program Director Rich Couse’s recent blog post.
