Portland, Oregon Wisteria produces a lovely spring show, but this tenacious vine requires a lot of pruning to prevent it from engulfing the entire garden.
Neil Bell, a horticulturist with the Oregon State University Extension Service, remarked that wisteria are “extremely vigorous vines and can climb easily to 30 to 40 feet.”
They should be grown on a sturdy structure because they can be rather hefty.
People want wisteria for their own gardens after witnessing the beautiful blooms explode in the middle of spring. But they should first be aware that the vine also requires intensive pruning in addition to the right support.
People should be aware of the work required to keep them in check before planting one, Bell advised. “Most flowering shrubs may be pruned once a year, but because wisteria is so incredibly vigorous, summer pruning is also beneficial. The biggest error is not pruning at all.
The Chinese species (Wisteria sinensis), which blooms on bare branches before foliage emerges with flowers that open all at once, is the one that is most usually planted. They are smaller than the Japanese wisteria (W. floribunda) blossoms, which unfold after the leaves emerge and gradually from the top down. The colors of fragrant flowers range from blue to lavender and, less frequently, white. Both kinds produce a lot of runners, which can be cut down more frequently than twice a year if the plant is in danger of taking over a building, particularly your home.
Winter is the best time to prune because the leaf has fallen and the runners are simpler to spot, according to Bell. Examine the vine, trim any extra growth to the trunk, and then trim the remaining runners to two or three buds or a length of about 6 inches. Just above the selected bud, cut. Again in the summer, you should trim any extra growth and leave only two to three buds.
Another choice is to educate your wisteria to grow into a tree, which enables it to develop far from any structures where, if unpruned, it could seriously harm them. When it comes time for cutting, Bell added, it also makes it simpler to maneuver around the plant.
Use a sturdy metal stake to hold the vine to form a tree. It can take one growing season to train one shoot to climb the support, he advised. The following year, cut the main stem where you want the branches to grow above the top of the support, and the tree’s basic shape will be finished. After this, the wisteria will require severe trimming every year to stay under control. The shoots can be severely pruned and still produce flowers.
Sometimes wisteria owners lament the lack of blooms on their plants. Be warned that, unless you purchased one while it was in bloom, blooms frequently don’t appear for two or three years (and perhaps longer) after planting. However, there are several things you may do to speed it up if you’ve waited for what feels like too long. Root pruning and stressing the plant by not fertilizing it will frequently force it to bloom. To root prune, cut the roots in a circle one to two feet from the plant’s trunk using a shovel.
Other growth advice from Bell for wisteria includes planting in full sun and maintaining continuously moist but not soggy soil. Use a low-nitrogen fertilizer (first number in the three-number label sequence). Less fertilizer is preferable to excessive fertilization. Feeding should only occur once a year, every other year, or never.
Fun fact: Sierra Madre, California is home to the largest known wisteria, which is over 1 acre in size and 250 tons heavy. In 1894, the Chinese species was planted.
How is wisteria grown in Oregon?
- Wisterias can get rather hefty as they mature. Build a strong fence, trellis, or arbor to support them. Wisteria vines can grow on living trees, but take precautions. If the vine girdles the tree trunk, it can destroy trees with a diameter less than 10 inches.
- The wisteria doesn’t bloom, which is the most frequent criticism. Before blooming, young plants require three to five years of growth, full light, though they may tolerate some shade, and soil that is reasonably healthy while also being moist but not overly wet.
- Plant wisteria away from areas where stems could encroach and clog drains.
- The entire plant, even the pea-like pods that develop following the bloom, is poisonous.
- As necessary, prune. Reduce the new tendrils to roughly three-quarters of their original length to encourage the plant to focus its energy on storing nutrients for the flowers of the following year rather than growing vines. Maintain the plant’s form via pruning. Keep it bushy and don’t chop it back all the way to the wood. Annual pruning preserves quality, prevents the vine from encroaching on
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Is wisteria capable of growing in the Pacific Northwest?
Wisteria may get fairly heavy and needs solid supports, therefore when it is planted, care should be made to ensure a suitable structure is being used, such as a sturdy arbor, pergola, or fence.
The young vine needs to be wound or tied to the vertical structure in order to provide Wisteria with some guidance. You can do this by carefully looping the young shoot around the arbor, pergola, or fence’s wooden pillar. Due to the fact that this trunk will enlarge with time, you don’t want to clamp it particularly tightly to the wood. As an alternative, you can teach the branches to grow vertically by attaching a string from the plant’s base to the top of your building. Wisteria is content to scramble across a horizontal surface, so after the vine has established itself on the top half of your building, you can remove it.
Many pieces of gardening literature make the assertion that American hybrid plants are less hardy or less likely to bloom repeatedly. Less tenacious is a pretty relative term, though. We are still dealing with wisteria, which may grow five to ten feet in a single season in robust specimens. Regarding flowering, you will often get a large rush of spring blooms and frequently another flush later in the summer under perfect growing conditions and with the right species for your climate (usually at about thirty percent of the volume of the spring bloom).
Here in the Pacific Northwest, a well-established wisteria should be in its bloom cycle in April or May, with Chinese cultivars blooming before leaf-out and American and Japanese cultivars blooming after leaf-out and just before Chinese cultivars. Sometimes during the growing seasons, very well-kept wisterias will blossom, although never to the extent seen in spring.
Some of you might be shaking your heads and saying, “My plant has never even blossomed once!” This is undoubtedly conceivable and might be connected to one of the following problems:
High-nitrogen fertilizers: If your plant is near a fertilized lawn or if you use one, you will be encouraging a lot of vegetative development at the expense of flowering (nitrogen, phosphorous, and potassium (N-P-K) strength is given numerically on packages, with nitrogen being the first number). Since wisteria belongs to the family of legumes and peas, it may have some nitrogen-fixing abilities, which would increase the fertilizer factor.
Light: Wisteria can thrive in areas with partial shade, but it needs at least six hours of direct sunlight for flowering.
Frost: Just like many spring-flowering plants, flowers or their buds can be harmed or even killed by a cold snap.
Disease and pests: This is quite unusual. Wisteria scale is the largest pest, but it’s not a huge issue in the Pacific Northwest. Wisteria scale has only ever been reported to Swansons once, in my experience. Given the size of wisteria plants and the density of the foliage, systemic insecticides are preferable to foliar treatments for treatment. If wisteria is planted very incorrectly or is cultivated in an area that is overly damp with inadequate drainage, it may occasionally have root rot or graft failure.
Water: Wisteria prefers soils that are fertile, moist, and well-drained. As a result, irrigation to a certain extent can be beneficial, especially if the plant is in a location that is particularly dry given our drier Mediterranean summers.
Wisterias are known for tolerating all types of aggressive pruning, however pruning that is done improperly or at the wrong time will significantly reduce flowering.
Maturity: When a plant is ready to flower, it is referred to as being “adult.” For certain plants, this process can take just one season or years. From seed, wisteria might take 20 years to bloom. Fortunately, this doesn’t happen very often in the nursery industry. The plants we observe, especially the hybrids and cultivars, are grafted or cultivated from rooted cuttings and begin to bloom at a young age—roughly 7 years.
Don’t worry too much if you planted wisteria this year (or perhaps a few years ago) and it didn’t bloom. It may take some time for wisteria to establish itself and begin producing its stunning flower show on a regular basis. Up to 7 years may pass before very young plants begin to blossom freely. However, I have read reports of plants blooming in their first year after planting. Fortunately, producers usually make the plants available to us when they are 4–8 years old, so once planted properly, you won’t have to wait very long for blossoms.
However, there are a few things you may do to encourage flowering the following year if you have an older plant that either won’t flower or does so intermittently (i.e., once every few years).
I’ll start with the fundamentals: root pruning and nutrients. The second article in this series will discuss pruning, which is by far the best strategy for encouraging re-blooming.
Where can wisteria be found?
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.
Native Wisteria
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).
Non-Native Wisteria
- 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.
The greatest places for wisteria trees to grow
The greatest way to utilize wisteria’s breathtaking beauty and incredible vitality is to grow it as a little tree, or standard. Long racemes of sweet-smelling May flowers hang down from soft, pruned leaf heads and sway slightly with each breeze. The compact head of a Tree Wisteria looks amazing in a mixed bed of perennials, bulbs, and annuals. The impression is beautiful and dignified.
Please be aware that wisterias typically take a while to emerge from dormancy after planting. Please be aware that your plant won’t start to leaf out until early summer. It will thereafter leaf out at the usual time in succeeding years (midspring).
Choosing a Location: Wisterias grow and flower most effectively in areas with plenty of sunlight, preferably at least 6 hours every day. They do well in any kind of soil as long as it drains well.
In order to plant your bareroot Wisteria, take off the packing and give the roots a few hours in a bucket of water. Then, dig a hole that is both large enough to permit the roots’ spread and deep enough to allow you to set the crown, or the location where the stem and roots converge, 1 inch below the soil’s surface. Insert the roots into the planting hole and arrange them naturally or like the spokes of a wheel. The roots of many woody plants are brittle, so use additional care when positioning them in the planting hole to prevent breaking them. With one hand holding the crown 1 inch below the soil’s surface, use the other to push soil into the hole while circling the roots to prevent air pockets from forming. Then, using both hands, compact the soil close to the crown. To create a basin, create a rim of earth around the perimeter of the planting hole. This basin is used to collect, hold, and direct water to the roots. Finally, thoroughly immerse the plant.
Please be aware that once bareroot plants are taken out of their packing, they dry up rapidly, especially on a sunny, windy day. Until you are ready to plant, we strongly advise that you keep the roots wrapped in wrapping material.
Staking: To keep their heads aloft in severe gusts, tree wisterias need additional support. After planting, drive the wooden stake that came with your tree 6 to 12 inches deep and 1/2 inch away from the plant’s trunk into the earth. Using the plastic tie tape that came with the tree, affix the trunk to the stake numerous times, spacing them apart by about 8 inches. You’ll need to swap out the original stake for a bigger wooden stake or a sturdy steel pipe as the head and trunk grow bigger. Check the tree every spring and autumn to ensure that the stake is securely in place and that the tie tape used to attach the trunk to the stake is not excessively tight and preventing the trunk from expanding. Plants need to be firmly staked at all times.
Watering and Fertilizing: To hasten wisterias’ establishment in the first year after planting, they require the equivalent of 1 inch of water each week. If the sky doesn’t provide enough moisture, water deeply once a week. Plants that are established only require irrigation during extended dry spells. Wisterias don’t need much, if any, fertilizing because too much fertilizer prevents blossom. Give plants a gentle feeding of 5-10-10 or 5-10-5 at a rate of 3/4 cup per square yard in the early spring each year if your soil is particularly weak or sandy.
Overwintering: For the first few winters after planting, cover the main stem with a piece of plastic tubing in cold-winter conditions like ours here in Litchfield (Zone 5 [-20F]). To encircle the stem, make a straight incision from one end to the other and pry the cut open. (Precut tubing could be available at your nearby garden center.) To stop wind and frost from damaging branches on older specimens, cat’s-cradle bind the branches together using twine to form a web of intertwined strings.
Pruning: Tree Wisterias need to have the long, twining branches they generate in the summer pruned lightly but frequently in order to maintain the globe shape of the head. A couple of weeks prior to the first date of your first frost, they also require one severe pruning in late summer or early fall. Remove all branches that are in the wrong place and reduce the current season’s development to just 5 to 6 huge buds (leaving stubs that are about 6 inches long). This drastic haircut inhibits growth and promotes the transformation of some leaf buds into flower buds. Don’t let pruning errors keep you up at night. Wisterias are highly understanding plants; strong growth the following season will give you another chance.