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.
Can wisteria trees be grown in Wisconsin?
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.
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.
The best results and least detrimental effects are frequently obtained when manual, mechanical, and chemical control techniques are combined.
- 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.
- 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.
Is wisteria able to endure in Wisconsin?
The genus was named after Caspar Wistar (1761–1818), a professor of anatomy at the University of Pennsylvania, but Nuttall, the inventor of the genus, spelled it Wisteria; the spelling Wistaria was an adaptation.
The best time to fertilize your wisteria is in the fall, despite the fact that we feed many of our shrubs and flowers in the spring.
If you’ve ever seen photographs of Monet’s garden or have really been there, you can’t help but be mesmerized by the lovely wisteria clinging to the rails of the bridge over the water lily pond. It is a thick vine covered in gorgeous violet-blue or lavender blooms, which give off a lovely scent. Wisteria is simple to cultivate, but you should exercise caution because it may quickly take over your yard, porch, and house and won’t bloom if you don’t give it the right care.
Chinese wisteria (Wisteria sinensis), Japanese wisteria (Wisteria floribunda), and American wisteria are the three most popular types of wisteria in the United States (wisteria frutescent). Chinese wisteria blooms in the spring and is more widespread than Japanese wisteria. In zones 5 through 8, it can survive. Summer-blooming Zones 4 through 9 are ideal for Japanese wisteria to grow. A less widespread variation, the American wisteria (wisteria frutescent) thrives in zones 6 through 9 and blooms in the late summer.
Since wisteria is a vine with a reputation for rapid growth, the place in which you plant it in your yard should be your top priority. Since wisteria is a twining vine, it needs a strong support and regular pruning to stay in check. While their vines are growing quickly and generating leaves, many gardeners find themselves unhappy since they aren’t seeing any of the blooms that wisteria is supposed to produce. Wisterias don’t bloom for a variety of reasons, but with a little knowledge, the issue can be resolved.
Too much nitrogen in the soil is the most frequent cause of wisterias failing to blossom. Too much nitrogen will cause wisteria plants to generate a lot of foliage but no flowers.
An essential plant nutrient, nitrogen encourages lush, green foliage in plants. Other crucial plant nutrients are potassium and phosphorus. However, if you use a lot of animal manure, the level of nitrogen in your soil might occasionally become excessive. Testing your soil will show you how acidic or alkaline it is since soil nitrogen levels alter over time. A pH of 6.0 or lower indicates extremely acidic soil, which may be too nitrogen-rich for your wisteria.
- Testing your soil to see how acidic or alkaline it is should be done initially.
- If your soil test indicates a pH under 6.0, you should limit nitrogen-based fertilizer. Use organic mulch and compost, both of which contain less nitrogen.
- Plant cover crops that fix nitrogen. Grasses and legumes, like fava beans, are good options to grow in these regions because, when they are harvested, extra nitrogen will stick to their roots and be drawn out of the soil.
- Dig hydrated lime into your soil as an alternative to planting nitrogen-fixing cover crops. If the soil is sandy, apply 4 ounces of lime per square yard; if the soil is clay, apply 12 ounces per square yard.
- Digging organic items into your soil to increase pH and assist neutralize excess nitrogen is another nitrogen-fixing option. Good options include oyster shell, crushed marble, bone meal, and hardwood ash.
- Although it is possible, root pruning is better left to the professionals.
If your soil has been analyzed and found to not be overly nitrogen rich, you might want to think about the following.
When properly “planted,” everyone thrives, and wisteria is no exception. When wisteria vines are stressed, they may not flower but instead sprout leaves in the absence of full sun or sufficient drainage.
Your wisteria’s potential to blossom may be delayed by improper fertilizer as well as the timing of your fertilization. In the spring, fertilizing can promote leaf growth while discouraging blooming. In the fall, you should fertilize your wisteria.
Wisteria maintenance demands skillful pruning methods. Without trimming, wisteria vines have the potential to reach heights of 100 feet or more, making any blossoms the plant produces impossible to see. Wisteria’s new lateral branches should be cut back to 6 inches by midsummer. It should be clipped once more to the same effect in late winter. Once the vines begin to bloom, prune as soon as the blossoms start to fade and once more in the late winter.
The problem can also be a lack of maturity. The majority of wisteria that customers buy from plant nurseries are mature enough to begin blooming. However, if you received your wisteria from a friend or grew it from seed, it might not yet be mature enough to bloom. Typically, wisterias bloom three to five years after being planted. Some wisterias take up to 15 years to mature. Wisterias grown from seeds may take up to 20 years to blossom or they may never do so at all. However, the flowering process can be sped up with proper planting, pruning, and maintenance.
If you offer your wisteria the ideal environment, you’ll get wisteria blossoms that even Monet would envious of!
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.
How resilient to cold is wisteria?
It is well known that wisteria take a very long time to bloom. For two to three years after planting, don’t anticipate blossoms. Some readers swear by the following technique to encourage blooming:
- To cut into part of the roots, take a shovel and drive it 8 to 10 inches into the ground approximately a foot and a half away from the main trunk of the wisteria.
- Approximately half of the roots should be damaged for the shrub to be shocked into reproduction (flowering).
- Don’t worry—impossible it’s to harm this unchecked, unwieldy, frequently invasive shrub!
- The flowers of wisteria can also be impacted by chilly winter temperatures.
Consider growing a wisteria species that is indigenous to North America if you live there, such as:
- Wisteria frutescens, also known as American wisteria, thrives in zones 5 through 9. Its original states span from Virginia to Texas, the southeast to Florida, and up into New York, Iowa, and Michigan in the north. The vine is 25 to 30 feet long, has glossy, dark-green leaves, and after the plant has begun to leaf out, develops huge, drooping clusters of lilac or purple-blue flowers. Only new wood will display the blossoms. Notably, the blossoms are typically less aromatic than those of Asian wisterias.
- In zones 4 to 9, Kentucky wisteria (Wisteria macrostachya) flourishes. Similar to American wisteria, this late-bloomer is a native of the Southeast of the United States (it is sometimes considered a variety or subspecies of American wisteria). The Kentucky wisteria is the quickest to blossom, bearing faintly fragrant bluish-purple flowers after only two to three years of growth.
- A gorgeous, silvery-blue cultivar of the native Kentucky wisteria called “Blue Moon” is particularly hardy. In late spring or early summer, it blooms. It can go as chilly as -40F. (-40C).
- Despite the fact that they are frequently marketed at nurseries and garden centers, Chinese wisteria (Wisteria sinensis) and Japanese wisteria (Wisteria floribunda) are non-native, invasive species, hence we do not suggest them for North American gardens. They can reach lengths of 30 to 60 feet and are hardy in Zones 5 to 9. (and beyond in the Southern U.S.). Japanese wisteria comes in two popular kinds, including:
- Popular plant known as “Honbeni” displays clusters of pink flowers in the late spring.
- “Alba” (also known as “Shiro Noda”) yields beautiful clusters of snow-white flowers in the late spring.
Are Wisteria Toxic to Pets and Humans?
Yes, 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.
If pets or young children frequent the area, it is a good idea to remove the seedpods after the plant has flowered because the material is particularly concentrated in the seeds and seedpods. Unaware children or animals won’t think twice about eating as many seedpods as they can because they are not unpleasant to taste or have an instant effect. In case of ingestion, contact your neighborhood poison control center.
Wisteria can 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 can it grow in Zone 5b?
This is not a difficult plant to cultivate if you have plenty of sunlight, space, and a strong support. It prefers good drainage and a slightly alkaline soil and is hardy to zone 5. When it is in bloom, it requires a lot of water and does best in an area protected from severe winds. As legumes fix their own nitrogen and adding more will diminish flowering, avoid feeding them with high-nitrogen fertilizer.