We just bought a house in Nanaimo with a very old and neglected wisteria vine. It is huge and although it rests on a pergola, it's winding up under the eaves, on the roof, and up against the windows. We have no idea how to prune this vine and would appreciate any tips. Most literature recommends a February pruning and then another pruning in the autumn; is this consistent with this climate? Also, there seem to be mixed views on how much/little to fertilize. Thanks for all help.
Thin out unwanted mature stems in winter (January) and head back new growth in summer (July). Overwintering flower buds occur in spurlike twigs that must be watched for, not broken or pruned off if flowers are to be seen. In this manner wisteria are similar to apple trees, although their flowering spurs are even more fragile and easily lost to clumsiness or lack of awareness. If your climber is all over the place it may not need to be fertilized at all. At any rate, always sample your soil and have it analyzed before fertilizing. Use soil test report to choose appropriate formulation, if any fertilizing is indicated.
This article on Plant Amnetsy is the best piece written on wisteria pruning that I have seen yet. It sounds like what your wisteria needs is some form of "renovation" prunng. Renovation pruning can be done at any time, but it's the easiest to handle when the plant is dormant, so you can have a better appreciation of the configuration of the vines, and you don't have to deal with the mounds of foliage. 1. Be prepared to prune without mercy - you need all the cutting tools that you have in your arsenal, all freshly sharpened - secateurs, loppers, pruning saw, and even an electric reciprocating saw if what you have is a big specimen. 2. The idea of renovation pruning is getting it into a shape and size that you can live with and then some more - several feet more (remember, you have to allow for the fact that there will be regrowth after the pruning, and you have to allow room for that) 3. Start off with the major vines/trunks - take out any that you don't want or has strayed into a space that they shouldn't be. Cut those out completely down to their points of origins. 4. With the remaining vines, prune them back to 2-3 feet shorter than your envisaged dimensional boundary of the plant. 5. Next, turn your attention to the smaller, but well established and woody laterals arising from these main vines. Remove any laterals that are overcrowded. Shorten others to the desired length. To ensure some flowers for the current season, leave those laterals that end in a cluster of stubby laterals. These are the laterals - "spurs" - can be depended upon to continue to give you some flowers after the major pruning. 6. Now, you should have reduced that monster to a manageable size. For the final finishing touches, remove all young runners that are not needed, or that stray into places that you don't want to be - e.g., under the eaves, into the sidings, etc, of the house. Cut them back to their points of origins. Once these are removed, turn your attention to the remaining runners - reduce each and everyone of these to 3-6 buds. Once you have accomplished "renovation", don't expect much blooms for 2-3 years. The response of the wisteria to aggressive pruning is to "fight back" and literally explode with new runners. It's going to put energy into vegetative growth at the expense of flowering. This is where ongoing maintenance pruning is important: 1. Remove all unwanted runners right to their points of origins. 2. Prune back the others to 3-6 buds (leaves). Repeated pruning of these runners is what will eventually give you "spurs" of woody, short laterals that in turn will provide you with blooms. 3. You need to prune these runners all season long - I check and prune my wisterias once every 2-4 weeks. 4. in the winter, or better still, spring after flowering, size up the plant again, and perform minor "renovative" pruning to further get the plant into the shape you want. 5. Do not fertilise - they do not flower well if there is an over-luxuriance of vegetative growth. Over feeding also ends up with you fighting a constant battle with a monster of an plant which thinks it's an octopus. If you have well fertilised beds in the vicinity, the long reaching roots of the wisteria will eventually find them. I put a sharpened shovel through the soil between the wisteria and nearby beds, to prune any roots that might have wandered over to indulge in the nutrients over there. No one says maintaining a wisteria in good form is easy. But I find pruning it surprising relaxing, and the flowering of a well trained wisteria is one of the major high lights of my gardening calender.
