Oleander is a lovely flowering bush with a fragrant scent and long-lasting flowers, and it should not be pruned until after it has stopped blooming. It will bloom all summer and into fall, so the best time to prune oleander is in September and early October. Make sure you prune it early enough in the season so that new growth will have time to harden off before the first hard frost.
Oleander is extremely poisonous and even the sap can cause serious skin irritation. Wear long pants, long-sleeved shirts, and gloves when pruning. Clean your shears carefully after pruning.
The main reasons to prune oleander are to remove dead or damaged wood, to promote branching, and to make it bloom more profusely. Remove all crossing, damaged, dead, or diseased wood, and cut any unwanted stems at ground level. Shape the rest of the plant by cutting the tips just above the leaf nodes. This will cause the plant to branch out and set more blooms. If you want a really bushy plant, let the newly pruned branches grow for a while and then cut them back again. This will force even more branching and produce a full, flower-covered plant.
Pull suckers at the base of the plant if you want the bottom of the plant to be cleaner and more tree-like. Also, be careful not to prune more than a third of the existing foliage for best results.
All parts of the oleander are extremely poisonous and can cause death if ingested. Skin contact can cause serious rash. Do not burn the clippings of oleander as the smoke is also dangerous to humans and animals. Bag up the debris and dispose of in the trash.