Although wisteria in flower are one of the most beautiful plants on earth, they can be problematic. Most common is failure to bloom. The answer is to never fertilize them, with one important exception.
Since they are legumes, members of the bean family, they produce their own nitrogen. But it’s phosphorus they crave, in the form of triple super phosphate powder. For a mature plant, sprinkle 4 to 6 cups in a large area around the base of the plant. This is best done late February to early March and usually results in a tremendous bloom. Forget all the other bad advise about wisteria, such as root pruning. Wisteria crave water, and the more the get the faster they’ll grow.
Japanese wisteria (Wisteria floribunda) grow in a counter clockwise fashion and come in blue, white, purple or pink. They leaf out soon after they bloom, somewhat obscuring the flowers.
Chinese wisteria (Wisteria floribunda) come in the same colors, but have an important distinction. They bloom on bare wood and don’t leaf out until much later, creating a breathtaking display that can last two weeks or more. They grow in a clockwise direction.
Wisteria are big burly plants and can cover literally hundreds of square feet. The flowers are edible and considered a delicacy in Asia. Any sturcture on which they grow must be extremely strong. They also can be trained to a “standard” in which all side shoots are taken off every fall, leaving a central leader. When the leader reaches 8 to 10 feet in height, they are allowed to branch out, in effect creating a wisteria tree.
