Q.Hibiscus buds have white crust on them
Buds and tips of branches have white crust on them. These plants are in big pots.
Certified GKH Gardening Expert
This could be an insect infestation with scale insects. Mealybugs and anow scale are two types of scale insect that can attack hibiscus. See these articles for help:
https://www.gardeningknowhow.com/plant-problems/pests/insects/control-plant-scale.htm
http://garden.org/nga/searchqa/answer/85344/
http://www.extento.hawaii.edu/kbase/crop/type/p_strach.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/mealybugs-control.htm
http://entnemdept.ufl.edu/creatures/orn/mealybug/mealybug.htm