My broom bushes do not get yellow flower and I don’t know why. Been planted for about 5 years. Had flowers when I planted them but never bloomed again.
Certified GKH Gardening Expert
It could be the quality of your soil, or not enough sun. If they are getting full sun, then I would recommend fertilizing at least once per year in spring. This article will give you more information on their care: https://www.gardeningknowhow.com/ornamental/shrubs/broom-plants/how-to-plant-broom-shrubs.htm