For best results, your wisteria should be planted in well-drained soil, and should receive a minimum of six hours of full sun. Be sure to have sufficient space for the full canopy to develop - 15 feet minimum is ideal. You may need to provide a stake for the tree for the first few years until the trunk can support the weight of the canopy. The vine requires support to grow up on- a sturdy wood or metal structure is best.
Cut those Branches Back! - Pruning Wisteria
Wisteria requires pruning twice a year - once in the summer after blooming, and once in the winter. Keep in mind that wisteria blooms on wood that is at least two years old - so don't be afraid to prune hard.
In the summer, after the beautiful flowers have faded, prune the branches back, so six to eight inches remain on each branch. Pruning that amount off will encourage branching to develop further, increasing the number of blooms the next season. Remove any shoots that are growing at the base of the plant you do not want. Lower shoot pruning will most likely need to be done every year.
Come winter, prune the branches down to about three to five buds. Reducing the branch length will force the energy in the spring into creating flowers, and you will have a prolific flowering season. Remove any long shoots that may have formed after the summer pruning. Since the foliage has dropped and you can better see the structure of the plant, this pruning will be easier than the summer pruning. The flower buds that form in the summer will be what produce blooms the following spring. Make note of this fact and make sure that you do not remove or damage all of the buds. Otherwise you may stifle next season's blooms.
Root pruning is optional - it can help further develop the root system of the plant, but is not required. If you choose to root prune, take a sharp shovel and plunge it into the soil. Don't tip it taking it out, but instead go straight in and straight out. Make a series of slices into the root mass around the entire plant for best results.
Feeding your Wisteria - Fertilization
Nitrogen fertilizer is not needed - wisterias are a legume plant, and can produce its nitrogen as it develops. In fact, adding nitrogen fertilizer can decrease flowering, as it helps the plant produce leaves, not flowers.
[caption id="attachment_5622" align="alignnone" width="620"] Aunt Dee Wisteria Flower[/caption]
Its Not Blooming! - Trouble Shooting
If your wisteria is not blooming, it is most likely an environmental issue. Check to see that your plant is getting at least six hours of direct light during the day - that is the absolute minimum wisteria requires for blooming. If it is not, see if you can increase the time by pruning other plants.
Temperature is another factor that may negatively impact blooming. If a late frost comes before blooming, the buds may be damaged and will not flower. Unfortunately, there isn't much you can do to correct this issue except wait for the next season. If you know a late frost is coming, you can cover smaller plants with sheets to help protect them.
If you have added a significant amount of nitrogen fertilizer to your wisteria, it may be encouraging it to produce leaves instead of flowers. Wisteria does not require nitrogen fertilizer - they can create their nitrogen in the soil, much like beans do.
If your plant is young, it may not be mature enough to flower. If after two to three years of being planted in the ground, and it still is not blooming, check to make sure the environmental conditions are correct.
Enjoy your wisteria and it's beautiful flowers!