Oleanders do not require pruning to be healthy, but some pruning will result in a bushier shrub and allow you to achieve your desired shape. Oleanders are easy to cut, and a good pair of hand-pruners will usually do the job.
Cut just above leaf nodes
A leaf node is the point where three leaves have sprouted from the branch. Cutting just above it forces new branches to grow, resulting in a fuller, bushier plant.
Remove no more than one-third of the plant
Oleanders are fast growers, so annual pruning may be necessary to maintain the desired shape and size. As a general rule, do not remove more than one-third of the total branches in a year.
Prune in late summer or early fall
The time to prune oleanders is right after they finish blooming, usually in late August or early September in Northern America. This gives new growth a chance to harden off before winter. Pruning too late can leave new shoots exposed to harsh weather.