Is my wisteria dead, can I save it, or do I need to start over?
Our patio had an amazing 50-ish year-old wisteria growing on a 25 foot long pergola. For the 8 years we’ve owned the house, it grew like wildfire every summer, my husband pruned it moderately 2-3 times a season, and it was always flush with purple blooms in May and again most Augusts (sometimes we'd even get flowers throughout the summer). We’ve also never experienced any winter die back, though it blooms very late in May before the leaves come out. We had a gardener do a real hack job on it in 2012, they actually just went along the edge of the pergola with a chainsaw with no regard to what was being cut. I thought it might die from the severe pruning, but it seemed to bounce right back in 2013 with great spring blooms. Then last spring, 2014, we had a particularly harsh winter for Lower Michigan, followed by a late frost and the vines never budded. All season in 2014 there were no leaves anywhere on the older vines. We did have numerous new vines start growing out of the base to maybe 3-4 feet up. Yesterday, when I trimmed the vines (still no greenery yet, it's too early), I found that most of the older vines were dead and rotted, 3 inch diameter vines would just break in my hands, especially in the older sections. I fear there is no vine left to save on the top of the pergola. Worse yet, I now believe the vines that were growing last year are from the root that may have been grafted to the original vine, so not actually the same wisteria. The new vines have buds (I could find no buds on the older vines), but at the base of the bud, pointing down, were small thorns – my wisteria never had thorns before. I am crushed to think this amazing wisteria may be dead, but I also realize I can’t keep wasting season after season hoping it will “come back”. If it’s dead, I want to get going on growing a replacement as soon as possible. But if there is any chance at all of saving the original vine, I’d like to try. What do you think? Is there anything I can do to save the vine? Should I try cutting it back, completely removing it from the top of the pergola? Should I try stressing the roots to make it grow? Or is the vine too far gone? Are the new thorned vines a sign that it is growing off the grafted root and I should give up on it? If I replace it, do you have a species to recommend? I have no idea what the original was, but apparently it is rare for most wisteria to have such profuse blooming. Could it have been the age of the vine and not the species that contributed to that? Also, how should I replace it? It has ~1.5 foot diameter base now, in a 3-foot circle surrounded by my concrete patio. Will I be able to pull out the base and roots for a new planting? If so how? Will I need to use a stump grinder instead? Can I immediately plant a new wisteria there? Or should I wait for the roots to rot and how long?
Oakland County Michigan
The top of the wisteria evidently died during the winter of 2013-2014. The roots were still alive and that's where the new shoots came from. Wisterias are not grafted; they are seed grown. On the stems, there are two spine-like projections on the top sides of each leaf scar. Those are the little thorns. They are supposed to be there. You are not going to find them on the disintegrating dead wood; they fell off long ago.
From what you have said, there are no older big vines still alive. The plant is trying to grow back from the roots. Stressing the roots will not do anything other than damage or kill what is trying to grow now. That's more probable than the age of the vine. You have been exceptionally lucky with flowers.
But I am amazed it did as well as it did growing in a hole in the patio. Surface roots have something called respiration aiding them. The roots take in air, use the carbon dioxide and make oxygen. That cannot happen when they get no air. This is a vital part of healthy plants.
Wisteria are hardy to zone 5... that's -10 to -20 degrees. The winter it died, we had multiple times it went below twenty below zero, sometimes as much as -28. It happened this February, too. This is another contributor. Lack of root respiration and temperatures too cold for plant cells is the probable cause of failure.
I have no idea how you are going to get roots out of a three-foot hole but if you put another wisteria in, the weather may get it before lack of root respiration. Right now, you have a great deal of buried wood from large roots. A stump grinder only would grind the stump, not radiating roots blocking soil. And a company that would take a stump grinder into this area is looking at creating a great deal of damage to the hardscaping.