Oleander, Nerium oleander, is a flowering shrub that grows well in climates with mild winters with few or no frosts and freezes. Oleander shrubs typically grow 8 to 12 feet tall, gaining 1 to 2 feet of growth each year. They blossom in large, showy flower clusters from early summer until midautumn. Oleander's vigorous, multi-stemmed growth habit makes pruning necessary for training and maintaining a desired size and shape.
Prune away all dead, old, overgrown or cold-damaged growth from your oleander shrub annually in early spring. Cut the branches back to the main stem or trunk.
Deadhead the spent flowers by picking them off the oleander as they begin to fade and wilt. Removing the dying flower clusters promotes prolonged blooming into the fall.
Trim back the stem tips on your oleander right after the shrub is finished flowering in autumn to promote healthy branching. You can also cut back the branches on the oleander as desired to the nearest healthy buds in order to control the shrub's size and shape.
Train your oleander into a tree-like form instead of a multi-stemmed shrub by cutting all the stems back to the ground, except for one main stem. Perform this pruning in early spring while the shrub is still young. Remove all suckers or water sprouts that emerge from the base of the oleander or its roots every year. Cut back to the ground all stems or growth that emerge parallel to the main stem or trunk each year to maintain the oleander's tree-like form.
Rejuvenate or retrain an older, overgrown oleander by cutting back 1/3 of the older stems to the ground level in autumn. The following autumn, cut back half of the remaining old stems and trim back the long shoots from the previous year's new growth. In the third year, prune away the rest of the remaining old stems and trim back the new shoots again.