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Japanese wisterias appreciate moist soil. There is some evidence that vines located near ponds do better there than elsewhere. However, they do not require regular supplemental watering. Only when they are first planted and during drought is it necessary to water them. When rainfall is sparse over a period of time, check soil moisture below the soil surface to see if you need to water. Use a sprinkler or soaker hose to get gradual penetration to a depth of 10 to 12 inches. Water only during hot, dry weather, every week or 10 days. Some deprivation encourages blooming. For information on products see the file on Choosing Watering Equipment
Sprinkle a fertilizer on the soil over the roots of wisterias each spring while they are getting established. Once the main stem has achieved the ideal height, discontinue feeding. This will minimize lush growth of leaves and stems and encourage blooming. Ironically, nutritional deprivation seems to stimulate flowering. For more information see the file for Fertilizer Products
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Mulching helps control weeds, conserves soil moisture, and keeps the sprawling root system cool. Lay 2 or 3 inches of peat moss, chopped leaves or shredded bark on the soil at the base of the vine out about 2 feet around. This will also protect the vine trunk from damage by mechanical yard care equipment. For more information see the file on Using Mulch
Pruning is the key to an attractive wisteria vine. As it is maturing, cut the main branches back severely, as much as half, in the late winter. If there are buds, this will remove some of them, but it will stimulate growth the following season. Reserve most severe pruning of wisterias that bloom until late summer or fall. Also thin out side shoots emerging from main stem, and trim flower-producing spurs back to 2 or 3 buds. This encourages it to fill in its allotted space. Prune any vine stems that failed to blossom, saving those few necessary to extend the length, or height, of the vine. Once the wisteria has achieved the desired proportions, stop annual fertilizing. From this point on, prune shoots back in summer by half, then prune all shoots back to 4 or 5 buds every winter to eliminate excess growth. Regularly cut out any weak or damaged wood and all suckers coming up from the base. They may be coming from below the graft and will not be the same type of wisteria vine as the main one.
It is not necessary to prune off the seedpods that develop from the flowers. Their presence does not affect future blooming of the vine. For more information see the file Choosing Pruning Tools
A wisteria vine requires very sturdy supporting structure to climb on. Plant it at least six inches from its support to allow for sufficient air circulation. It will follow its own whim and crawl over a pergola or dead tree, twining as it goes. If it is to climb the side of a building, attach supporting wires to brackets that protrude at least 6 inches out from the wall. Do not locate the vine beneath the drip line of eaves or gutters, lest the soil be too soggy. String galvanized wire or pipe (wood strips are not strong enough) vertically to the height desired, then horizontally in a double row measuring about 2 feet between. Be careful to keep the wires at least 2 feet below the eaves so that the vine will not be tempted to crawl onto the roof or into the attic.
After planting the wisteria, identify the strongest shoot (or two, if a double stem design is desired) and attach it to the vertical wire. It will willingly twine itself around the wire to create the leader, or main trunk, of the vine. Clip off all other tendrils. As this leader grows and sends out side branches, attach them to the horizontal wires where they will form shoots that bear flower buds. When the vertical leader, or trunk, reaches the maximum desired height, pinch it off so that all subsequent growth is horizontal.