By Amy Witt, Horticulturist, UMaine Extension Cumberland County, email@example.com
HWA is a serious pest of eastern hemlock and can kill a tree within a few years of being infested. For more information, see the Maine Department of Conservation’s HWA overview.
By Dr. Lois Berg Stack, Extension Specialist, Ornamental Horticulture, Univ. of Maine; Dr. Mary Rumpho, Professor of Biochemistry and Molecular Biology, Univ. of Maine; and Dr. Donglin Zhang, Associate Professor of Horticulture, Univ. of Maine. For more information, contact firstname.lastname@example.org.
Asiatic bittersweet (Celastrus orbiculatus; also called Oriental bittersweet) was introduced to the United States in the late 1800s for ornamental purposes: it was long planted as a decorative vine in landscapes, and it has also been used in crafts such as wreathmaking and floral design. It has become a difficult weed in many home landscapes, and has become widely established in the eastern U.S. and Canada, where it is a serious invasive plant in natural areas (see photo of bittersweet on Mackworth Island, Maine).
What does it look like?
Photos by Lois Berg Stack
This vine grows to 30’ and longer. It climbs by twining its stem around supports such as trees. The stems have light brown bark covered with bumpy lenticels. The leaves, 3-5” long, are arranged alternately on the stems, and are oval to nearly round, with a pointed tip. The root surfaces are bright orange. This plant is dioecious; that is, male flowers and female flowers develop on separate plants. Only the female plants produce clusters of colorful yellow fruits that split open in fall to reveal orange-scarlet seeds (see photo of immature fruits that have not yet split open).
There is a native species of bittersweet, American bittersweet, but the two can easily be differentiated by comparing two features. First, the leaves of American bittersweet are narrower, more “oval” than “round.” And second, the fruits of American bittersweet are located in clusters only at the tips of stems, while the fruits of Asiatic bittersweet are located on side branches all along the vining main stem. This feature explains why Asiatic bittersweet was introduced, as it is more colorful when in fruit.
What kinds of sites does Asiatic bittersweet invade?
Asiatic bittersweet grows at the edges of forests, in open woodlands, and in fields and hedgerows. It grows most vigorously in full sun, but tolerates shade and invades forested areas. In those shaded sites, if a tree is cut or falls in a storm, the increased light often causes the existing small bittersweet seedlings to grow rapidly and climb up trees around the opening. Asiatic bittersweet readily invades sites with slightly acidic and moderately moist soils. It tolerates a wide range of temperatures, and is invasive from eastern Canada south to Georgia, west to Arkansas and north to Wisconsin.
How does it invade new sites?
Female Asiatic bittersweet vines produce large numbers of seeds. Although lab studies have shown that they do not remain viable much longer than one year, the seed bank in the soil is quickly replenished each year by annual crops of seed. Birds disperse seeds to new sites, often flying from an infested site to a wooded nesting area and dropping seed there. People are part of the picture, too, when they purchase wreaths or arrangements made from Asiatic bittersweet and discard those items in places where birds can eat the seeds and later disperse them.
Once established in a site, the plants often spread by root suckering. In landscape settings, for example, if Asiatic bittersweet is planted in a bed, and the bed is edged with a sharp tool, the severed roots beyond the bed often send up new shoots.
What impact does this plant have on native species?
Asiatic bittersweet is outcompeting its American counterpart in two ways. First, it is more competitive, and is displacing the American species. Second, it hybridizes (naturally) with its American counterpart.
When an opening in wooded sites allows this plant to grow rapidly, its shade restricts the growth of native understory shrubs and groundcovers. Bittersweet stems can, over time, restrict flow of sap in the trees which it entwines. As the vines increase in size and weight, the trees under them are more susceptible to damage from wind, snow and ice.
How can I control Asiatic bittersweet?
No single method controls this plant. By combining the following methods, you can manage it:
If I remove this plant from my landscape, what can I plant in its place?
Many vines are available at garden centers and nurseries. Native American bittersweet (Celastrus scandens), native riverbank grape (Vitis riparia) and native trumpet honeysuckle (Lonicera sempervirens) are all sold by some nurseries. For possible vendors in Maine, check Bulletin #2502, Native Plants: A Maine Source List. For smaller vines in more refined landscapes, consider clematis hybrids.
Where can I find more information about this plant?
Check our fact sheet Asiatic Bittersweet or call your local Extension for print copy.
Drip irrigation, sometimes referred to as micro-irrigation, delivers small amounts of water under low pressure to plants through a network of strategically placed tubing. This approach to watering has many benefits and is appropriate for all types of gardens including: containers, vegetable & ornamental beds, raised beds, and even hanging baskets. An increasing number of local retailers offer the basic equipment to put together a home system, and there are numerous on-line retailers that sell the materials as well.
Why install a drip irrigation system in Maine?
Materials commonly used in drip irrigation
Note: Starting at the water source, these items are listed in the order in which they are normally located within the system.
Timer: Although not essential, most drip irrigation systems have a timer. If a timer is used, it is helpful to install a Y-connector at the water source so that a separate hose can bypass the timer when necessary.
Filter: A filter is a good idea for any water source, but is especially important when the water source is a well or pond. Filters remove small particles, such as soil, in the water to prevent emitters from clogging.
Pressure reducer: Water pressure varies from place to place and is often quite high, which results in blown out lines. A pressure reducer rated to approximately 40 pounds per inch2 (psi) will protect your irrigation system from the damaging effects of high water pressure. Be sure to check the irrigation emitters to determine what range of water pressures they will tolerate.
Irrigation tubing: Gardeners have three main options for irrigation tubing. The simplest form is a soaker hose: a porous-walled garden hose that allows water to slowly seep into soils. Another option is drip tape: a thin-walled plastic tubing that has holes at pre-set intervals. Thick-walled plastic tubing is the third option. In this case, the installer decides where the holes should be. High quality thick walled tubing is recommended for long-term applications.
Fittings and valves: These are mainly used with thick-walled plastic irrigation tubing, but may be used with soaker hoses or drip tape as well. These include “L” and “T” shaped connectors that direct the tubing around corners and in diverging directions. Used in conjunction with shut-off valves, these can be used to establish different irrigation zones within the garden. If an area isn’t planted, the valve can be closed off to minimize water use.
Emitters: When using thick walled irrigation tubing, holes are punched into the tubing and small, barbed emitters can be inserted into the holes. Different emitter types have different output rates. Smaller sized tubing can be connected to emitters to apply water to areas further away from the main line. Some choose to not use emitters, simply letting the water to flow out of the tubing holes.
Goof plugs: These handy items plug holes in the irrigation line that are not in a desirable location. Goof plugs save you from being stuck with emitters in the wrong location and from replacing a whole irrigation line.
Even though Maine has relatively high annual rainfall totals, precipitation throughout the growing season can be unreliable and is often insufficient for optimal plant growth. A consistent water supply throughout the entire growing season is essential for producing high quality, high yielding plants. Drip irrigation is an efficient solution meeting your garden’s water needs.
For more information:
Hutchinson, M. Trickle Irrigation: Using and Conserving Water in the Home Garden. University of Maine Cooperative Extension Bulletin 2160. http://extension.umaine.edu/publications/2160e/
Broner, I. Drip Irrigation for Home Gardens. Colorado State University Cooperative Extension publication 4.702 (1998). http://www.ext.colostate.edu/pubs/garden/04702.html
Parsons, J., S. Cotner, R. Roberts, C. Finch, D. Welsh, and L. Stein. Efficient Use of Water in the Garden and Landscape. Texas A&M Extension. http://aggie-horticulture.tamu.edu/extension/homelandscape/water/water.html
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Image Description: Hemlock Woolly Adelgid; photo by J. F. Dill
Image Description: Asiatic bittersweet growing over trees
Image Description: Asiatic bittersweet berries