Ask-a-Dave's-Gardener: My flowers are turning brown and dying!!!, 3 by BlossomCA

BlossomCA wrote:
Dear Experience Gardeners

I'm new to gardening and not doing so well as many of my plants are doing poorly also :( I attached 3pics to show the problem, first one is my mini rose that the flowers turned brown and died before full bloom and some of the leaves turned yellow also. The second pic is Lantana's flower buds just turn brown and no idea if they're even gonna become flower and the last pic is Lion's tail's flower buds turned brown after blooming. And i grow Desert rose that the buds just turned brown and fell off before become flower. Now i spray them with Neem oil but only one time last Thu but l plan to do again this Thu.
If anyone please help me with this situation to safe my beautiful plant.
Thanks very much