To get my wisteria to bloom next year, when is the best time to add phosphorus?
Wisteria Doesn’t Bloom
Certified GKH Gardening Expert
Amend the soil around the plant in the fall with 1/2 lb of colloidal sulphate or bone meal, both of which are good sources of phosphorus. You may also want to add in some rotted manure if you have it. Keep in mind, however, that depending on other factors and the age of the plant, blooming isn't guaranteed but this should help alleviate the problem.