Wisteria only one flower branch went yellow?
Newly planted rest of vines growing other flowers coming but the first bloom is now going yellow?
Certified GKH Gardening Expert
If it is newly planted, then you will expect a recovery period. You may not see good flowering until next year ,or the year after. This article will help you to care for the plant: https://www.gardeningknowhow.com/ornamental/vines/wisteria/growing-wisteria-proper-wisteria-vine-care.htm