Q.fruit tree care
Just planted orange tree, grapefruit tree and dragon fruit tree in Florida. How often do you water? When should we fertilize them?

Daily water for newly planted trees is very important for the first 2 weeks. You can generally cut back after that but if temperatures are above 85 degrees you will need to likely water more.
Here are some links for you.
https://www.gardeningknowhow.com/ornamental/trees/tgen/watering-newly-planted-tree.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/tip-on-water-requirements-for-citrus-trees.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/fertilizing-citrus-trees-best-practices-for-citrus-fertilizing.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/tip-on-water-requirements-for-citrus-trees.htm
https://www.gardeningknowhow.com/edible/fruits/trifoliate-orange-tree/trifoliate-dragon-orange-tree.htm