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Elisabeth C. Miller Library

Keyword: Wisteria

Non-blooming Wisteria

We have a Chinese wisteria which we’ve had for 20 years. We’ve
trained it on a trellis to the side of our covered porch and then
on a rope across the front so there is a nice green, leafy fringe
along the porch front. However, this plant has never bloomed.

We have consulted with our local horticultural experts and they have suggested various treatments. The lawn care
people do not fertilize near the roots of the wisteria so it
doesn’t get too much phosphorus, we have done root pruning, we have
even hit the trunk with a board to shock it, have applied super
phosphate but no blooms. We get some pretty cold
winters, but I’ve never even seen flower buds anywhere on the
plant. I know wisterias are sometimes late in blooming, but this
is a long time to wait! The roots of the plant face east and get
lots of sun. The part across the porch is shaded in the afternoon
because we have two pine trees in the front yard. We prune off the
tendrils that form during the summer to keep the plant in check,
but what else can we do to get blooms? I know it would be a
spectacular display if it ever bloomed and have almost given up
trying. I’m thinking of hanging artificial blooms just to get the
effect!

 

 

I found quite a bit of discussion in online gardening forums about
flowerless wisterias, so you are not alone. You may find this information
from Cass Turnbull of Plant Amnesty helpful:

“THE MOST COMMON COMMENT I get at classes and at the PlantAmnesty
educational booth is, “My wisteria won’t bloom.” It is natural for these
vines to take between three and seven years to start blooming. I have
read that frequent, proper pruning may help them to begin blooming
sooner, or at least more. On the other hand, some people have old vines
that have never bloomed. I am told that these are seed grown plants or
“mules.” I have often heard root pruning recommended to force an older
vine to bloom. Basically, this means that you use your shovel to cut the
roots in a circle (or dotted circle) a foot or two from the vine. I have
also heard people recommend fertilizer formulated to encourage blooms,
(not heavy on nitrogen). However, I have been faced with such a vine and
had no luck with either technique. In that case, as with all
non-performers, removal is the best option, and no one will blame you for
it.”

Here are gardener Ketzel Levine’s comments, from her NPR.org site:

“Depending on how old your wisteria is, do know that young plants can take
up to eight or ten years before they flower, especially if started from
seed. Other reasons wisteria fail to bloom: lack of adequate sunlight
(needs at least six hours of full sunlight); too much nitrogen fertilizer
(causes more vegetative growth); pruned heavily in winter or spring (also
encourages vigorous vegetative growth); severe winter injury/cold-blasted
flower buds (though that is clearly not a problem this year) or a bum
plant. It happens.”

You could either try the method described above, of cutting a circle with
a shovel, or you could replace the vine, or you could follow through on
your artificial flower idea! (I’ve heard that Bellevue Botanical Gardens
hangs Wisteria-shaped lights from their arbor for their holiday light
show.)

,

Wisteria: the Complete Guide

When I was nine, our family moved to a new home in the Sammamish Valley that included a wonderful, if somewhat overgrown, garden that fostered my interest in horticulture.  Near the back door, plopped in the middle of the lawn, was a strange, dense thicket of a plant that was a perfect place to hide, mere feet from where my mother was calling for me.

It was some time before I learned this monstrous green blob was a wisteria, left to its own devices with nothing to climb up.  The new book, “Wisteria: The Complete Guide” by James Compton and Chris Lane, has enlightened me that wisteria can indeed be grown in a pleasing, shrubby form, but only with careful pruning that the specimen of my childhood never received.

Of course, wisteria are much better known as climbing vines magnificently draping from buildings, arbors, or even large trees.  This book walks you through the many selections available, with excellent photographs to distinguish the many close shades of blue, lavender, and purple, and will help you manage one of these labor intensive but oh-so-spectacular prima donnas.

This is the third in a series of excellent Royal Horticultural Society monographs on garden worthy genera and like the others titles the natural history and environmental niche of the plants are extensively examined.  “As befits a vigorous and twining climber, Wisteria has a rather tortuous taxonomic history” and includes as principle players the great Swedish naturalist Carl Linnaeus and Thomas Nuttall after whom Cornus nuttallii, the Pacific dogwood, is named.

The cultural history of wisteria, especially in China and Japan, is another highlight while other chapters profile spectacular specimens – they can live for hundreds of years – from around the world.  There is one notable example in Sierra Madre, California.  Planted in 1894, it “took over the house it was originally planted on and now spreads through the gardens of two neighbouring houses.”  It covers about 1.25 acres and “has entered the Guinness Book of World Records as the largest blossoming plant.”  I never realized the peril that threatened my childhood home!

 

Published in Garden Notes: Northwest Horticultural Society, Fall 2020

pruning wisteria

I have a wisteria that has gone untamed for a few years, and I need to know when and how to go about pruning it back to a reasonable size. It grows up the fence to a pergola-like structure, but it’s gone way past that to begin attaching itself to surrounding trees.

Local pruning expert Cass Turnbull of Plant Amnesty has written about pruning wisteria. Here is a link to the article on Plant Amnesty’s website. The relevant passage (about renovating an out-of-control vine) is excerpted below:

RENOVATION. If it gets away from you or you have moved into a home that already has an enormous wisteria tangle, grabbing and strangling everything in sight, show no mercy. Lop, saw and chain saw whatever is necessary to get it back down. I suggest you cut several feet below where you want the regrown vine to be, since you will experience an upsurge of new shoots the following spring. As with all heading cuts, the new growth occurs directly beneath the cut and heads up from there. You will need some room to let it regrow over the next few years. New
growth will be vegetative (not flowering) and rampant for a few years. I wouldn’t be surprised if some major stems die back partially or totally, if you make cuts one inch or over. But I doubt that you will kill the plant. As some stems die back, cut off the dead bits. Others will supply the replacement shoots to be tamed in upcoming years.

Local gardener Ciscoe Morris also has information about maintaining wisteria vines. Excerpt:

“To prevent damage to your house and to encourage flowering, prune the tendrils to about 4 inches from the main structural vines when they grow beyond a foot long. This is a form of spur pruning. It encourages flower buds to form by concentrating all of the energy that would have been used to grow the long tendril into a 4-inch stub. While you are at it, you may as well construct a shed under the wisteria to store your ladder, because within only a few weeks, new tendrils will begin to grow and you’ll be climbing up to do it all again.

The Royal Horticultural Society also has information on pruning and training wisteria in an article entitled Pruning and Training Wisteria.

According to the American Horticultural Society’s Pruning & Training (edited by Christopher Brickell; DK Publishing, 1996), the times to prune are midwinter and again in summer, about 2 months after flowering. With
an established wisteria, the goal of regular pruning is “to control extension growth and to encourage the production of lateral flowering spurs. The current season’s shoots are cut back in two stages to within two or three buds of their base. These will bear the coming season’s flowers. Growth and flower buds are easily distinguished in late winter,
the former being narrow and pointed, the latter plump and blunt.”

plants for screening

A friend asked me about screening two large propane tanks that, unfortunately, have had to be placed in front of their home on Camano Island. She mentioned wisteria to me and I shuddered. I’ve seen this plant do a lot of damage to trellis and home alike. Can you recommend, instead, an evergreen solution to this problem?

I am not familiar with the size and shape of propane tanks, but perhaps evergreen shrubs might work to screen them. A concern would be the proximity to the house, and any needed clearance for paths, doorways, and windows. I think you are right to avoid Wisteria. Does your friend prefer the idea of planting vines, or would shrubs be acceptable?

Here are a few suggestions for evergreen shrubs, with links from the local web site, Great Plant Picks:

Some good information is also available about plants for screening (from Virginia Cooperative Extension) and vines, especially evergreen vines such as Trachelospermum jasminoides, which might be a good solution. Local garden writer Valerie Easton on has written helpfully about hedges, as well.

pruning and training Wisteria

Is it all right to cut off the hanging pods from the Japanese
Wisteria? Will cutting them have any adverse affects to blooming next
year? Some are hanging so long that we keep walking into them! Maybe I should cut them and bring them inside for decoration.

 

Cutting off the seedpods on your Wisteria is not a problem, just be
careful not to cut the stems back too far (unless you are intending to
prune, which you can certainly do if you need to control growth) as there
may be buds further up which will be next spring’s flowers.

Fine Gardening online has a helpful illustrated article on wisteria pruning which includes the following:
“Some seedpods may be left on the vine for winter interest, but just know that if you bring them inside, warm temperatures will cause them to explode.”

You may find the following links to general information on care and
pruning of Wisteria helpful:

 

Excerpt from an article, “Pruning Vines,” by Donald Hodel and Dennis Pittenger:

Pruning wisteria extensively during the dormant season may
encourage rampant vegetative growth the next spring.
Instead, in July prune out the long, straggly growth
except those branches needed for climbing. This is more
likely than anything else to induce flowering. Shoots
should be cut back one-third to one-half their length.
This will induce them to produce the short spurs that will
bear next season’s flower clusters.