Oleander is a warm- to temperate-season bush that grows quickly up to 20 feet tall. It forms a mound approximately 10 feet wide at maturity, which can become leggy as it ages. The plant produces masses of attractive flowers in pink, white, yellow, salmon and red. The lance-shaped leaves may grow up to 10 inches long. Oleanders are poisonous, so care should be taken when planting them where children and animals play. Oleanders are easy to grow and respond well to pruning. They make good subjects for training to a standard tree form.
Begin training at installation, if possible. Choose the straightest, strongest stem, and remove all the others at the soil level. This will be your leader and will form the trunk on the standard. Use gloves as you work with the plant. The sap can cause dermatological problems.
Cut off the top 2 to 3 inches of the bush. This promotes the formation of a thick, bushy crown. Cut off any branches that are less than a third of the bush's height from the ground.
Prune the top again over the next two seasons. Begin shaping it by removing branches that are errant and go outside the natural canopy shape. Continue to keep the leader clear. As the tree gets taller, the first bushy growth should be at 3 to 6 feet above the soil line.
Remove all the base stems at ground level except the straightest and two of the most healthy and strong flanking stems.The best time to do this is September to early October. In season two, you will remove these two, and leave only the one strong leader stem.
Trim the top of the bush back by up to 6 inches to force bushy growth. Tip prune the periphery of the bush to begin to establish a form. Tip pruning consists of removing end growth back to the next growth node. Cut just before the node.
Cut off any limbs that are more than 3 to 6 feet, or one-third the height of the bush, in season two. Clean up the main leader by cutting off at the trunk any new growth. In successive seasons, maintain by cutting out errant growth in the canopy and keeping the main trunk clear of sprouts and leafy growth.