The best time to prune a citrus tree intended for fruit production is after the tree fruits and before it flowers. If fruit production is not an issue and the tree is in a frost-free climate, prune it at any time. Annual pruning is usually sufficient.
Citrus trees are quite forgiving of pruning and usually grow back rapidly, but avoid pruning a citrus tree in the fall if winter frost is a possibility. They can be pruned into tree or bush shapes and are suitable for topiaries and hedges. Topping fruit-producing citrus trees makes harvesting the fruit easier and encourages bushier growth.