Prune oleander by the end of the summer, or early October at the latest. Pruning stimulates new growth, which needs time to harden off before winter arrives.
Oleander, a flowering shrub, can tolerate a great deal of pruning when done at the right time of year. Prune branches evenly and do not remove more than one-third of the branches. Stems that are broken, spindly, or rubbing against other branches should be removed. Take off branches at ground level, where they diverge from more mature stems.
Pruning oleander in the early fall makes more flowers emerge in the spring. Cutting an oleander branch above a leaf node forces three branches to grow from that spot.