I have a large wisteria in my backyard that’s over 20 years old – several trunks entwined together in a thick mass – and it blooms beautifully. How do I protect it during construction? Should I cut it back to the ground, or dig it up and put it in a large pot or temporarily replant it elsewhere in the yard until next spring?
Wisteria don’t transplant well and mature specimens often do not survive a move. When they do, it is several years before they bloom again. Avoid moving the plant twice , so transplanting to another spot and moving it back in the spring is not a good idea. As insurance, take cuttings from the vine and start them in a large pot that can be sunk in the ground over winter or until your construction is finished. Growing new plants from cuttings is easy, but they will also take a few years before they will bloom. The vines however will grow like crazy. There are several ways to do this:
Root cuttings and suckers: If the plant already has suckers growing around it, these can be dug up and planted separately. Alternatively if the plant has no suckers some of the root can be dug up, removed from the plant and planted separately. The root piece removed should be at least a foot long with a caliper of half an inch or more. It should be replanted so that the top of the removed root is just below the soil surface. It will generate new buds and send up a new wisteria shoot. Remember root cuttings and suckers will produce new plants that are the same as the original plants roots. If the original plant was a seedling or a rooted cutting the new plants will be the same. However, if the original plant was grafted the new root cuttings will not be the same as the original plant.
Layering: This is the easiest, if not the quickest, method to grow a new plant that will be the same as the original. A long one year shoot that can be pulled down to soil level is needed. A portion of the shoot is buried in the soil, but with the shoot tip still above the soil line. The part of the shoot that is buried can be wounded with a sharp knife, (a slice of bark is removed). After a year the shoot can be cut away from the main plant as the part that was buried should have made its own roots. This can then be transplanted to a new location. This method is may not be the one you will use if there are time constraints.
Softwood cuttings: Some wisterias root easily from softwood cuttings others do not. This method will work with some cultivars and not with others. Cuttings should be made from the new year’s wood in June, July or August. The cuttings should be about 6 inches (15 cm) long with one or two leaves, and should be nodal (the base of the cutting should be just below a leaf node.) Dip the cuttings in a rooting hormone, then stick them in a pot of any good compost. Place a clear plastic bag over the pot and seal it, to keep the humidity up and prevent them from drying out. Leave the pot on a windowsill or in a greenhouse out of direct sunlight. Rooting should start in 4 to 6 weeks.
As well as starting a new plant you can cut back the existing wisteria as much as needed. Try to protect the root zone around the trunk and hope for the best. It may survive, but blooming will be delayed.