I've been trying for years to get my wisteria to bloom, but all I get is green, leafy growth. Any ideas?
You are not alone. Wisterias are notoriously tricky plants to get blooming and there are several reasons for this.
The most basic is that the plant simply hasn't reached maturity. Wisterias are inconsistent in how long they take to mature. Some will get there in just a few years while others can take a decade or more. As a general rule, if the main trunk is less than the diameter of a broomstick, it's probably not going to bloom no matter how much you plead.
Another reason for the lack of blooms may relate to this vine's uncompromising need for sunlight. At least six hours are needed for wisterias to bloom, so site the plant next to the sunniest wall you have or get used to staring at a whole lot of green.
Wisterias also have a tendency to sacrifice their flowers in favour of prolific growth. This is especially true if they have access to a lot of nitrogen, a problem if they're planted next to a lawn that receives excessive fertilizer. A lack of fertilizer is rarely the reason why these vines don't bloom, so don't add it unless you have a good reason for doing so.
Additionally, improper pruning can cause a lack of flowers. If you're an enthusiastic pruner, try laying off for a couple of years to see if that's contributing to the problem.
Most plants will bloom if challenged. It's a function of nature that if a plant thinks it's going to die, it will make a desperate effort to reproduce. This is why many gardeners root prune their wisterias every year. The shock of having a shovel stomped through their roots forces them to flower like nothing else. Root pruning tends to make gardeners' nervous, but if you cut far enough away from the trunk of the plant, there is little danger of killing it. To root prune your wisteria, stomp a shovel into the ground about two feet out from the trunk and cut a semicircle into the earth.
For those of you who have not yet planted a wisteria, you can save yourself some trouble by restricting the root system when you first put the vine in. To do this, install a physical barrier at least 18” deep about three feet out from the base of the plant. The added stress of having its roots confined will encourage the vine to bloom.
If you have any questions or comments, please send them to me at vanessa@gardenmuse.ca.
Originally published in the Creston Valley Advance.
