If left to its own devices, a begonia bush will spread and branch, giving it a spindly, leggy look. To keep your begonia looking healthy and bushy, you must prune it regularly. If you allow it to get too overgrown, you'll have to prune its canes, and you may sacrifice many of next year's blooms. Cut your begonia's leaves in spring. Use a pair of sharp, disinfected bypass pruning shears and water after pruning to help it recover from the mild shock.
Examine your begonia bush for new growth. Begonias produce new growth from the tips of their shoots. Any new plant material will form a sharp tip at the end of the shoot. This pointy tip is a new leaf.
Cut the terminal leaf on the tip of your begonia's shoot. Use pruning shears to cut new leaves before or just after they unfurl. Left to its own devices, this shoot will continue to grow in one direction and give your shrub a leggy appearance. By cutting the leaf, you will force the begonia to produce more shoots that will fill out the begonia.
Repeat steps one and two until your begonia achieves the bushy look that you desire. Once it does, allow the shoots to continue to grow and fill out the plant.
Cut any begonia leaves that are damaged, yellowed or dead. Use pruning shears to amputate them right at the point where they join the shoot. Leaving these leaves in place may cause your begonia to develop disease.