Invasive Bittersweet Vines: All Bitter, No Sweet

If you’re reading this, it’s likely you live in the Chesapeake watershed. Assuming that’s true, it’s even more likely that you have seen bittersweet. It might be in your nearest park or forest, or even your own backyard, if you’re not a diligent invasive weed puller. If you live anywhere in the watershed, it’s definitely in your state (you too, DC).

Celastrus orbiculatus (commonly referred to as Oriental bittersweet, but we’ll just use “bittersweet” from here on) is a woody vine native to eastern Asia. It was brought to the US in the 19th century for aesthetic purposes, and has since established itself as a truly invasive species, and a scourge on our native forests. Like so many other invasive plants, bittersweet takes advantage of the abundant sun-exposed areas on forest edges, along roadways, around buildings, and areas freshly cleared of trees that are common in the more developed areas of our watershed. Bittersweet sprouts from the ground in leafy green shoots with broad oval leaves, then immediately begins to seek something to climb. At this early stage, the vines can form patches of dense growth that overwhelm the understory and shade out its native competitors.

A dense patch of bittersweet shading out the understory and climbing surrounding plants.

Unlike English ivy, which relies on dense mats of hairy-looking aerial rootlets to cling to its climbing surface, bittersweet climbs by tightly wrapping itself around the trunk and limbs of trees and shrubs. This often causes younger trees to become girdled, as the hard woody vine constricts the trunk. The vines continue to climb in search of the canopy while they increase in diameter and put out more leaves, shading out the leaves of the host tree. A single bittersweet vine can grow as thick as an adult person’s forearm, and growth rings inside of cut vines of this size reveal that bittersweet can reach 20 years of age. The vine will climb anything it can wrap itself around, and it grows very quickly. This makes saplings, smaller understory tree species, and shrubs particularly vulnerable to being overwhelmed by the constricting vines. Once a vine establishes itself in a tree, more vines will begin to climb it, resulting in a thick curtain of bittersweet clinging to the tree.

A bittersweet vine wraps tightly around the trunk of a young tree, causing it to become girdled.

As you can imagine, the weight of the dense growths of these vines can put tremendous strain on afflicted trees and shrubs. Add to this the fact that the host is already likely in poor health due to the infestation, and what results is a tree more susceptible to breaking from added strains like wind and ice storms.

Dense bittersweet growth climbs the trunk of a more established tree.

The good news is that bittersweet is easy to remove with just your hands and some simple tools. But before we talk about removal, it’s important to note that there is a native bittersweet (Celastrus scandens), commonly called American bittersweet, that looks very similar to its invasive cousin. The US Forest Service has a handy guide to help differentiate the two species, so it’s worth checking this out before you go wild with your clippers. However, the invasive bittersweet has been shown to greatly outcompete and hybridize with American bittersweet, making it far more likely that you will encounter the invasive variety.

To get started, you’ll want a pair of gloves and some clippers. A handsaw will make quick work of any vines that are too thick for clippers. When bittersweet is smaller and has not yet started to climb, it is easily pulled from the ground. Like any other weed, grasp the stem close to its base where it meets the ground and pull it up. If the roots or part of the stem are left in the ground they will most likely re-grow, so remove as much of it as you can.

A young patch of bittersweet begins to establish, shading out potential native understory plants.

Vines that have begun to climb can be trickier. Once again, if you can, you’ll want to pull up the roots. If that’s not possible, sever the vine as close to the ground as possible. For vines that have wrapped around the trunk of the tree, you’ll want to make a “window cut” which involves making two parallel cuts a few inches apart on the same vine and removing the piece in the middle. This gap that you cut into the vine will prevent it from healing back together. Cutting the vine will kill all growth above the cut, so it’s not necessary to pull the rest of the vine from the host tree. The vines are usually so tightly wrapped that pulling them from the tree could damage the branches and do more harm than good.

Optionally, after severing a vine near its base, any portion of the vine hanging from a tree limb can be cut as high as you can safely reach. This might be more aesthetically pleasing and will reduce the weight burdening the limbs. Bittersweet produces bright red berries that attract birds, which then eat and spread these berries to new areas through their droppings. If you are cutting vines while the berries are out, you can consider clipping off the bunches and disposing of them in a trash can.

Bittersweet vines can grow as thick as a human forearm, like this one that was cut during the management process.

There are challenges and important considerations when opting to treat bittersweet with chemical herbicides. If you choose to go that route, Penn State Extension has created a helpful guide.

The broad oval leaves of a young bittersweet plant, preparing to climb anything nearby.

It’s important to keep in mind that no matter what method you choose, treatment will not be 100% successful the first time. However, each time you treat an area it will become easier, and if you are as tenacious as the vines, you will succeed in the end. Our forests are depending on you!