Can you deepen the purple color of a light violet wisteria with fertilizer or some soil additives.
Certified GKH Gardening Expert
Not usually, no. This will be determined by genetics. If they are older, then they may naturally lose color over the years. They will, more than likely, over time end up lightening up even more. This article will give you more information on the care of these: https://www.gardeningknowhow.com/ornamental/vines/wisteria/growing-wisteria-proper-wisteria-vine-care.htm