Wear gloves to protect your hands or if you have sensitive skin, because the sap of oleanders contains toxins that may cause a rash or irritation. Wash your hands to remove sap before touching others, eating food or touching your face, especially near your eyes. Oleander sap, even if diluted in sweat rolling down your brow, will severely burn your eyes.
Remove dead or broken branches of oleander any time of the year in the American Southwest. Use bypass pruners to remove branches less than 3/4 inch thick and use loppers for branches with a diameter between 3/4 and 1 1/2 inches.
Trim back oleander branch tips across the shrub in mid to late spring, immediately after the main flush of flower clusters subsides. Make the pruning cuts 1/4 to 1/2 inch above a lower branch junction, alive leaf or bud, on the lower naked branches. New growth and more flowers result four to eight weeks later, across summer and into the autumn.
Hand prune branch tips on the oleander; do not use shears, which will leave blunt, cut wounds on the evergreen foliage. Focus hand pruning on errant branches, branches that grow inward across the center of the plant, and upward or outward branching structures that spoil the shrub's symmetry