Wisterias are loved because they drip clusters of highly scented flowers, in shades of white, pink or purple. They require a lot of work, though, to get to that stage. Pruning and fertilising are the two most important aspect of growing wisteria. If the soil is deficient in potash, represented by the third number in a fertiliser formula, its resistance to disease is lowered and it won't bloom as well. It also won't tolerate the cold as it should. Apply potash when you apply your regular fertiliser.
Sprinkle the sulphate of potash on the soil around the base of the wisteria. Use 28.4gr per square yard.
Use a rake to scratch the potash into the top 1/2 inch of soil.
Water the fertilised area to a depth of 8 inches. This will help soak the potash down to the wisteria's roots.