How To Grow Wisteria

A SPECTACULAR ORNAMENTAL

Wisteria is one of the most spectacular of spring-blooming perennials. With its abundance of foot-long pannicles of flowers—most commonly lilac-blue—it is a traffic stopper. I once had an elderly woman with a carload of grandchildren stop in front of my house and ask if her grandchildren could come in the yard and smell my wisteria.

The beauty of wisteria in full bloom has been immortalized in Tiffany stained glass, which often depicts irises blooming in the foreground—a nice combination in the garden.

The two species of wisteria most commonly grown in home gardens are the Chinese wisteria (Wisteria sinensis) and the Japanese wisteria (Wisteria floribunda). The Chinese wisteria is usually the favorite, with its 6-12 inch flower clusters whose flowers open all at once before the foliage has expanded, creating a spectacular show. This vigorous vine can grow up to 100 feet. The flowers are lightly fragrant. The Chinese wisteria can usually be counted on to bloom three or four years after planting—although one of the most common complaints about wisteria is that some plants refuse to bloom for many years.

The Japanese wisteria (Wisteria floribunda) produces flower clusters up to 18 inches long, and they are very fragrant, but the flowers do not open all at once, and it doesn’t grow quite as large. (Believe me, at up to 80 feet, this is not a problem.)

WISTERIA IS EASY TO GROW

Wisteria is easily grown. In fact, the usual complaint about it is that it is too easily grown—and can be difficult to control. My wisteria—which I trained into a small tree—does, like all wisterias, send up unwanted shoots from the base, which must be removed as soon as they are noticed. It has also shown a certain predisposition to want to lean. Without support, it would probably just lie down on the ground. The solution to this difficulty it to provide a sturdy support to keep the trunk aimed in a generally upward direction.

In addition to these unruly traits, my “small” tree-wisteria has a tendency to produce an overabundance of top growth that, if not cut back, will eventually engulf everything in its immediate vicinity. Since my wisteria is planted next to a driveway, it often seemed bent on engulfing my daughter’s car, whenever I neglected the pruning for too long.

Because of these exuberant growth habits, wisteria is a good planting for “problem” areas, bearing in mind that it requires full sun if you want it to bloom.

When I first moved into my present house (a fixer-upper), the entire front yard was a gravel driveway. There was no front yard, in the traditional sense; the entire width of the house, from doorstep to street, was a gravel parking area. This setup was, of course, unattractive, so I set about creating a large island bed, roughly in the middle of this barren stretch of gravel, allowing for parking on both sides. I used stackable blocks, of the kind used for retaining walls, two blocks high and shaped into a rough oval, and filled it in with bagged compost/manure. If I had it to do over, I would use natural stone, since it has much more eye appeal, but for many island beds, you can’t beat these stackable blocks for ease of construction.

In this island bed, I planted flowers and bulbs, and a single wisteria, staked to train it to a tree form.

Wisterias are actually very large woody vines. VERY large wood vines. One nurseryman, in answer to a customer’s question as to the mature size of wisteria, cited the existence of 100-year-old wisteria in California, which, according to a news report, “is so large that it has received a place in the Guinness Book of Records. It has been named as ‘The largest blossoming plant in the world.’ This amazing wisteria vine is more than one acre in size and weighs 250 tons. It has more than 1.5 million blossoms every year with 40 blooms per square foot. The branches of this unbelievable wisteria vine reach an amazing 500 feet long.” So the above statement that Chinese wisteria grow to about 100 feet is perhaps intended to present the homeowner with dimensions that don’t boggle the imagination.

The sky is the limit.

With wisteria, you decide the size and shape. Don’t be afraid to prune them aggressively. You won’t hurt them. If you’re going to worry about them, worry that they’ll engulf the neighborhood.

WHERE TO PLANT WISTERIA

And they aren’t that difficult to control, especially if you’ve made a wise choice as to the location of the planting. Wise choices as to location include places where you can easily mow around the base of the vine/tree, and places that are well frequented. By the latter, I mean that it is best not to plant a wisteria in and “out-of-sight, out-of-mind” location. It should be in a location where any rambunctious tendencies are noticed early. An island bed surrounded by other flowering plants is a good location, since such an area will get regular maintenance. Planting a wisteria near a driveway also works to draw your attention to its pruning needs.

Older gardeners—or any gardener who doesn’t want to be bothered with onerous maintenance chores—will probably not want to grow wisteria on a large and high arbor or pergola, since this would mean that pruning would have to be done on a stepladder. A wisteria grown on a small arbor would probably not be a serious maintenance problem, however.

As with any vine, wisteria should not be planted next to the house, with the idea of letting it clothe the exterior walls in glory. When vines of any kind are allowed to grow up the exterior walls of a house, they will work their way under the siding and eventually pull it loose. I understand that it’s okay to grow vines on stone or brick exteriors, but I would be afraid for the wooden shutters and window frames—and afraid of pruning on an extension ladder. But that’s just me. Maybe you have a gardening staff, a list of suicidal roofers, and great homeowner’s insurance.

For most home gardeners, wisterias are best planted either on a very strong support, such as a sturdy garden arch or small pergola, or trained in the form of a tree. Vertical supporting members for a wisteria vine should be four-by-fours (at least), and horizontal supports need to be made of strong framing lumber. These vines are very heavy when mature.

While I’ve seen wisteria grown successfully on a simple lightweight garden arch, this is probably not a good long-term plan. As the vine matures, the weight will eventually overwhelm such a structure.

TRAINING WISTERIA TO GROW AS A SMALL TREE

I think the easiest way to grow wisteria is to train it into a free-standing tree form. In three or four years, it will grow into a cute little ornamental tree six to eight feet tall. In ten years or so, it should eight to ten feet tall. Wisterias usually begin to bloom when they are two to four years old.

The chief advantage of training a wisteria to a tree form is that there is no need to build a sturdy and expensive structure to support it. Training a wisteria as a tree is simple: Stake the main stem of the plant to a sturdy post set securely in the ground and remove all unwanted growth along the “trunk,” allowing only top growth. As the “tree” grows taller, growth along the “trunk” can be removed higher up on the plant, thus creating a taller “trunk.”

The key to doing this successfully is the sturdy post (such as a four-by-four) set securely in the ground. As the wisteria grows larger and heavier, it may lean so heavily on a less sturdy and secure post that it will push it over. This will allow your wisteria “tree” to list sharply to one side, and it could even decide to lie flat on the ground.

Since I did not take the precaution of staking my wisteria to a sturdy enough post, I wound up having to prop it up. I wedged the heavy base of an old birdbath against the trunk. This is a two person job: One person pulls the small tree so that the trunk is more or less vertical, while a second person wedges the base of the old birdbath against it.

Also, if your wisteria begins to list a little to one side, there is no reason why you can’t just cut away any offending branches (half the tree, if you feel like it) leaving behind those that are disposing themselves more or less vertically. You can’t hurt a wisteria, and the free-form wandering and generally upward curves will look charming as the “tree” matures.

Pruning helps to encourage bloom, and both summer pruning and late winter/early spring pruning are recommended. For the first few years, as the tree puts on growth, pruning will be mostly a matter of controlling top growth and keeping the “trunk” free of unwanted growth.

There will be no mystery to summer pruning; just cut away overly exuberant growth to maintain a tidy shape. All you are trying to achieve is to make your wisteria look like a pretty little tree—and keep it from engulfing your car during the night. Summer pruning will be an ongoing business, unless you are okay with letting the “top” of the tree assume very large proportions. In this case, the “top” of the tree will be all over the place, including weeping to the ground and waving restless tentacles in all directions. You’d have something quite out of the ordinary there.

In addition to summer pruning, it’s best to prune wisteria pretty hard in late winter/early spring. By this, I mean that long, thin branches should be cut back quite a lot. It’s hard to be specific and say something like, “Cut back long thin branches by one-half to two-thirds,” because I don’t know how much you pruned it in summer. Just cut them back so that the tree’s canopy is fairly small and tidy looking. You may also want to remove some smaller branches entirely, to reduce crowding.

You can also prune after flower buds are clearly noticeable in spring—or prune both before and after buds have clearly formed. (Frankly, you can prune wisteria any old time.) Just be mindful to avoid cutting away any buds unless it’s necessary to the tree’s shape, and be careful about knocking the buds off by accident. Late winter/early spring is also a good time to raise the tree’s canopy by removing branches from the upper part of the “trunk.”

You can now pimp your tree. This is ever so much fun! A tree-form wisteria is a great place for a hummingbird feeder—and a couple of brightly painted birdhouses—and other decorations, too, such as wind chimes or sun-catchers. It’s also a nice place to hang a winter bird-feeder.

IF YOUR WISTERIA DOES NOT BLOOM IN A TIMELY FASHION

One of the most frequent complaints about wisteria is that the darned thing doesn’t bloom for many years after planting—and sometimes that mature wisterias do not bloom at all, ever.

Here are the usual causes of failure to bloom and suggested solutions:

1. Wisterias grown from seed are said to often take as long as 15 years to bloom, so most sources say you should grow wisteria only from grafted plants or cuttings of cultivated varieties of proven floriferousness and early bloom.

2. Wisterias that are slow to bloom can often be coaxed into bloom by a fairly hard pruning. An old, neglected plant may need very hard pruning. As a desperation measure for old and stubborn non-bloomers, root pruning is often suggested—where you dig around the plant with a shovel to sever some of the roots.

3. Wisterias should not be fertilized with nitrogen, as this tends to produce heavy foliage growth and no flowers. The best fertilizer for wisterias is phosphorus, in the form of bone meal or some other form of phosphorus. For this reason, if your wisteria is the centerpiece of a flowerbed, as mine is, give the wisteria a little space so that you can fertilize the flowers without giving the wisteria a dose. Alternatively, if you have flowers planted near your wisteria, hold off fertilizing them until the wisteria is already blooming. Of course, the spring bloomers—such as iris, English daisies, creeping phlox, and dianthus—flowers that need to be fertilized in early spring to produce a good display—should not be planted too close to wisteria. Flowers that bloom later in the summer, such as hibiscus, balloon flower, portulaca, and daylilies, can be given their dose of fertilizer a little later in spring without harm.

4. Wisterias need full sun. They won’t bloom in full or part shade.

GROWING WISTERIAS FROM SEED

Once your wisteria begins to bloom, it will produce large seed pods, which you may find useful for craft projects. Spray-painted gold or silver they aren’t half bad as Christmas-tree ornaments. But inside the seed pods are large seeds that are easy to germinate. The germination rate is pretty close to 100%.

The temptation to grow wisteria plants from seed to give away to friends and neighbors is hard to resist. One year, before I read that wisterias grown from seed are often slow to bloom, I planted quite a few wisteria seeds in pots, and I had many eager takers. I hope I did not doom these friends and neighbors to fifteen years of frustration, waiting for the plants to bloom.

I also gave away volunteer wisteria seedlings that came up in neglected flowerbeds in my yard. One of these plants was sprawling on the ground in full bloom before I noticed it—so I guess it must have been two or three years old. So, clearly, some seed-grown plants bloom young.

GROWING WISTERIAS FROM CUTTINGS

But if you’d like to give away wisterias—or feel you’d like another plant or two for yourself—it is equally easy to grow wisteria from cuttings. This approach will assure you of producing a new tree or vine that will not take forever to bloom.

Take cuttings from green softwood in late spring or summer. Cuttings should be 6-8 inches long and have a few sets of leaves. Remove leaves from the lower half of the cutting, but keep two or three sets of leaves on the top half. The places where leaves were removed (leaf nodes) are where the roots will develop. Trim the bottom of the cutting so that the lowest node where leaves were removed is ½ to ¼ inch from the bottom end of the cutting. Make this bottom cut at an angle.

Make a 2-inch deep hole in a moist soilless potting mixture. If you are using a 6-inch pot, you can fit up to five cuttings in one pot—and taking several cuttings is good insurance. Separate pots for each cutting may be the best idea, since you may want to grow them on in pots to avoid planting out in very hot or dry weather, or you may want to give some away, if they all come to good.

Put the bottom ends of the cuttings into the holes and firm the soil around them. Cover the pot with plastic. A 2-liter plastic soda bottle with the bottom cut out will work to cover a 6-inch pot, or you can use a plastic bag supported by sticks, so that the plastic can’t come in contact with the leaves.

Put the potted cutting in a sunny spot, but out of direct sunlight, and water regularly to make sure the soil doesn’t dry out. The cuttings should root in 4-8 weeks.

Once the cuttings have rooted, it would be best to grow them on in pots, gradually hardening them off (while making sure they have plenty of water). Usually it is too hot, and sometimes too dry, for successful transplanting into the ground in mid and late summer. It’s best to wait for the heat to break before planting out in the early fall. Make sure to water the newly planted cuttings regularly, once they’re planted out.

Wisteria plants grown from stem cuttings can be expected to bloom in 2-3 years, at which point you will be the envy of the neighborhood.

Cuttings of wisteria need to be taken from the softwood. This is wood that is still green and has not developed woody bark. The cutting should be about 3-6 inches long and have at least 2 sets of leaves on the cutting.