Ask Mr. Smarty Plants

Wisteria sinensis, as you obviously already know, is an invasive import from China. This website from the Plant Conservation Alliance has more information about the problems and techniques in removing the plant from the landscape. Unfortunately, you are gardening in Florida where the introduced wisteria is an even greater threat to native landscapes. It can grow up any support many feet into the air, girdling and eventually killing mature trees, taking over structures, and shading out other, more desirable plants. You are to be applauded for deciding to remove it.

As you also undoubtedly already know, this isn't going to be an easy task. We discourage the use of herbicides if at all possible. In the first place, there is always the possibility of accidentally damaging a desirable plant. In the second place, there is the problem of disposal; if you find you must use it, check with local waste collection to find out if they have a "hazardous materials" disposal date, so your leftover herbicide will not have a chance to get into the water supply.

So, our recommendation is that you roll up your sleeves. First, to make the situation more manageable, start taking down the stems. Using a pruning saw (and don't worry about damaging the stems, that's what you're trying to do), start cutting the stems into lengths for easy disposal. Be sure to rake up and dispose of any seeds or pods left behind. And note that one of the ways this plant spreads is by suckers, so keep an eye out for those and pull them out. If there is a community composting site in your area, where the compost is tended and turned faithfully, the compost should get hot enough to destroy the seeds of the wisteria. Otherwise, it will need to be bagged and added to the landfill. Now, having made the roots more accessible by removing the trunk and stems, go after the base of the plant. Depending on the age and size of the existing plant, this is going to require some digging and more sawing. Theoretically, removal of all the leaves needed for nutrition should kill the plant, but Nature is tenacious, and the aforesaid suckers will continue to appear from the roots in an attempt to survive. Keep pulling or digging out and cutting off chunks of the stem until you feel satisfied that you have gotten as much as possible.

We really don't think it's a good idea to plant something else in that spot right away. It would be better to watch the ground over the winter, continuing to pull out root as possible, and certainly destroy any suckers that show up. If you start another fast-proliferating plant, even a native, there is the likelihood that it will just be cover for more wisteria suckers popping up, and they could get themselves established before you realize they are there.

This is a classic example of why the Lady Bird Johnson Wildflower Center is centered on the protection and propagation of native plants, and the avoidance of non-natives, invasive or otherwise. It's much easier to not plant an invasive alien than it is to get rid of one.