Many popular garden species have recently been added to Wisconsin’s expanding list of restricted and forbidden plant species.
More plant enemies that have already escaped domestication in gardens and landscapes to affect our natural wild habitats are the focus of this week’s installment of my examination of some of these restricted invasive plant species.
The list of plants generating worry in our state and the Midwest keeps growing and includes trees, shrubs, aquatic plants, vines, and non-native wildflowers.
Because of this, it’s possible that garden centers and nurseries will be permitted to sell specific invasive plants for a while.
With its unique, lobed leaves and smothering habit, porcelain berry can swiftly suffocate trees near the edge of a forest as well as in shaded areas.
Due to its exquisitely marbled foliage in shades of green, silver, white, and a hint of pink or lavender, the variegated form quickly gained popularity.
This vine may quickly grow throughout woodlands and forest margins and is a prolific berry producer.
Long a favorite of water gardens, yellow flag iris’ tall, flamboyant flowers adorn wetlands in the middle of spring and the beginning of summer.
Yellow flag swiftly forms impenetrable clumps that quickly stifle native marsh plants. It spreads through seed that is carried by the wind and waves on the lake.
This charming, variegated, low-growing plant has been used for a long time as an ornamental ground cover because it spreads swiftly and looks lovely all year long.
Tansy, also referred to as gold buttons, is a tall, fragrant, and attractive non-native plant that quickly fills waste spots and arid areas with its enormous clumps of fern-like fronds.
The traditional, taller type is the one that is deemed invasive. Many of the more delicate, tiny, and white-flowered cultivars are exempt from restriction.
Wisteria is a popular climber for many local gardeners because of its traditional beauty and exotic, dancing clusters of pea-like blossoms on towering vines.
In reality, studies have revealed that the majority of wisteria plants in our region are crosses between the two, posing an even greater danger.
In Wisconsin, is wisteria prohibited?
To suggest a legal classification for each species taken into consideration for NR 40, Species Assessment Groups (SAG) were formed. This department-developed literature review [PDF] served as the foundation for the wisteria recommendation.
Identification
Woody vines with one-foot-long, alternating, pinnately compound leaves make up the leaves and stems of this plant. The edges of the leaves are slightly wrinkled. Older vines can grow to be more than 15 inches in diameter.
Blooms: Large, drooping racemes of showy, fragrant pea-like flowers (clusters). Blue-violet to lavender in hue.
Fruits and seeds: Velvety seed pods that range in hue from brown to gold. Pods are between four and six inches long, tapering at the base and enclosing every seed. One to eight brown seeds per pod are flat and rounded.
Few, big, and deeply embedded roots. Additionally, plants have stolons or runners that spread out horizontally across the ground and produce new plants.
Similar species: Wisteria frutescens, sometimes known as American wisteria, is a native of the southeast of the United States. The seed pods are smooth rather than velvety, and the flower clusters are smaller. The nursery industry does not frequently report on this species.
Control
The best results and least detrimental effects are frequently obtained when manual, mechanical, and chemical control techniques are combined.
Mechanical:
- Cutting can effectively prevent desired plantings from becoming strangled. Smaller populations or populations that are impermeable to treatment with this work best. Cutting must continue in order to gradually deplete root stores because plants regenerate after harm.
- More study is required on the use of fire for control. Visit the USDA Forest Service’s Fire Management Considerations for further details on using controlled fire to reduce wisteria.
Chemical:
- For huge vines, cut-stump spraying of glyphosate or triclopyr has been successful. For seedlings, foliar sprays are the most efficient.
- Foliar herbicide application guidelines (from Miller, 2003):
- Use one of the following herbicides in water containing a surfactant to thoroughly moisten all the leaves.
- When regrowth emerges from July to October for subsequent years, Tordon 101 at a 3 percent solution (12 ounces per 3-gallon mix), Tordon K at a 2 percent solution (8 ounces per 3-gallon mix), or Garlon 4 at a 4 percent solution are all effective treatments (15 ounces per 3-gallon mix).
- Transline as a 0.5 percent solution in water (2 ounces per 3-gallon mixture) when safety to surrounding vegetation is sought from July to September for successive years when regrowth emerges.
- repeated administrations of glyphosate in a 2 percent solution from September to October (8 ounces per 3-gallon mix).
- Links to more in-depth control information can be found under the Resources Tab.
Can wisteria be grown in the Midwest?
A show-stopping spring garden feature is lush wisteria covered with plump flowers. Read up on how to pick and train one before committing to this aggressive vine. Then you won’t have to deal with the problems that come with a pushy plant while you enjoy its delicious blooms.
Wisteria will it endure the winter?
Don’t panic if your wisteria begins to drop its leaves in the fall. Deciduous wisteria predominates. Winter doesn’t keep it green, but the leaves will come back in the spring.
Before dropping their leaves, some wisteria varieties put on a show of fall color as the leaves turn yellow or gold. If it’s happening in the fall, there’s typically nothing to worry about unless you’re also observing other symptoms like an insect infestation. Yellowing and dropping leaves can be signals of disease and other problems.
While Evergreen Wisteria (Millettia reticulata) is more challenging to grow, all true Wisteria are deciduous. Your Evergreen Wisteria will most likely maintain its leaves throughout the year if you have hot summers and brief, mild winters with little below freezing. This is zone 9b and higher in the US, which includes a portion of California and Arizona as well as the southern half of Florida and Texas.
Evergreen Wisteria is deciduous like regular Wisteria in more temperate regions, so you may anticipate it to go dormant for the winter and sprout new leaves in the spring. You probably won’t be able to cultivate Evergreen Wisteria in a location that is colder than USDA zone 8 because even deciduous habit cannot shield it from prolonged, bitterly cold winters.
What states are able to support wisteria?
In the spring, wisteria blooms ferociously, producing clusters of lilac-colored flowers on fresh growth that develops from spurs off the main stalks. Check out our Wisteria Growing Guide for more information on wisteria maintenance, including planting and pruning.
About Wisteria
Wisteria is a long-living vining shrub with cascades of blue to purple blossoms that, in the spring and early summer, look stunning hanging from a pergola or archway. However, this vine is known to grow fairly heavy and to grow quickly and aggressively, frequently reaching lengths of more than 30 feet. It’s advised not to put wisteria vines too close to your home since they will squirm their way into any crack or crevice they can find.
Beautifully fragrant wisteria flowers offer a feast for the senses. A brown, bean-like pod remains on the plant during the winter after flowering. There are only blooms on fresh growth.
Note: Be careful when planting wisteria! The wisteria plant contains lectin and wisterin, which are poisonous to people, animals, and even pets. If taken in significant quantities, these poisons can result in anything from nausea and diarrhea to death.
Is Wisteria an Invasive Plant?
The wisteria species Wisteria sinensis and Wisteria floribunda, which are not native to North America, are regarded as invasive in several areas. If you want to add a new wisteria to your garden, we advise choosing one of the native North American varieties, such as American wisteria (Wisteria frutescens) or Kentucky wisteria (Wisteria macrostachya), which are excellent alternatives to the Asian species.
Do you want to know how to distinguish between North American and Asian species?
While North American wisteria is not quite as aggressive in its growing tendencies and has smooth seed pods and fruits in addition to more-or-less cylindrical, bean-shaped seeds, Asian wisteria is an aggressive grower with fuzzy seed pods. Another distinction is that the flowers of American and Kentucky wisterias appear in the late spring after the plant has begun to leaf out, whereas those of Chinese wisteria do not.
When to Plant Wisteria
- Plant during the plant’s dormant season in the spring or fall.
- Wisteria can be grown from seed, although plants from seeds frequently take many years to mature and begin to bloom. It is advised to buy wisteria plants that are already established or to begin with a cutting.
Where to Plant Wisteria
- Put a plant in full sun. Even while wisteria will grow in some shade, it won’t likely bloom. Sunlight is necessary.
- Wisteria should be grown in fertile, wet, but well-draining soil.
- Wisteria will grow in most soils unless it is in bad condition, in which case you need add compost. Find out more about soil improvements and getting the soil ready for planting.
- Because wisteria grows swiftly and can easily engulf its neighbors, pick a location apart from other plants.
- Additionally, wisteria is renowned for encroaching on and infiltrating surrounding buildings like homes, garages, sheds, and so on. We highly advise against growing wisteria too near your house!
- Wisteria vines need a very strong support, like a metal or wooden trellis or pergola, to climb on. Plan carefully and use substantial materials to construct your structure because mature plants have been known to become so heavy that they destroy their supports.
Wisteria looks gorgeous growing up the side of a house, but use caution when planting it because it is a very strong vine that will get into any crack or gap!
Caring for Wisteria
- Apply a 2-inch layer of mulch and a layer of compost under the plant each spring to keep moisture in and keep weeds at bay.
- Phosphorus is often used by gardeners to promote flowering. In the spring, work a few cups of bone meal into the soil. Then, in the fall, add some rock phosphate. Study up on soil amendments.
- If you get less than an inch of rain each week, water your plants. (To determine how much rain you are receiving, set an empty food can outside and use a measuring stick to gauge the depth of the water.)
- During the summer, try pruning the out-of-control shoots every two weeks for more blooms.
Pruning Wisteria
- In the late winter, prune wisteria. Remove at least half of the growth from the previous year, leaving only a few buds on each stem.
- Also prune in the summer after customary flowering if you prefer a more formal appearance. On fresh growth, spurs from the main shoots of the wisteria develop its blossoms. Trim back every new shoot from this year to a spur, leaving no more than 6 inches of growth. So that there are no free, trailing shoots, the entire plant can be trained, roped in, and otherwise organized throughout this procedure.
- Mature plants that have been cultivated informally require little to no more pruning. However, for a plant that has been formally trained, side branches should be pruned back in the summer to 6 inches, then again in the winter to 3 buds.
- Possess you a fresh wisteria? After planting, aggressively prune the vine. Then, the next year, trim the main stem or stems to a height of 3 feet from the growth of the previous year. After the framework has grown to its full size, midsummer extension growth should be cut back to where it started that season.
Wisteria can be found in Chicago?
The American wisteria can reach lengths of 20 to 30 feet. It is a vine that twines. Twisting their stems or leaf stalks around a support helps twining vines rise. This kind of vine thrives on wires, arbors, trellises, and chain-link fences.
Flower description:
Clusters of purple, pea-like blooms. The clusters are shorter than those of Asian species, measuring 5 to 6 inches. They have a light scent. Mid-summer is when flowers are created.
Plant care:
Although it thrives in full light, this vine will also tolerate little shade. The ideal soil is moist, well-drained, and somewhat acidic. Prevent compacting. For the first five to 10 years, wisteria frequently don’t produce blossoms. Use phosphorus-rich fertilizer as directed on the label and nitrogen fertilizer sparingly to promote flowering. Pruning done correctly will also promote flowering. After flowering, cut down any extra growth to 6 inches. These trimmed stems will keep developing. Cut them once more in the winter, leaving two to three buds on each stem. In addition to promoting flowering, proper pruning also aids in controlling the vine’s size and shape. Wisteria vines weigh a lot and need strong supports.