Once we’ve had our first legitimate cold front/cool front, that’s the time in the calendar that you can and should prune back Oleanders. They can be rounded shrub form or even in tree form, but now’s still the time. First of all, pruning in early to late fall does help keep control of the growth habits, but since Oleanders bloom on new wood, this practice can only enhance the flowering for the coming year. However, fall pruning is not necessary each and every year. I learned from an old member of the Oleander Society years ago, that every other year is just fine.
Meanwhile, regularly removing dead, damaged and/or insect/disease infested limbs/branches can improve plant health, can and should be done. And I don’t just mean once-a-year. When I say “regularly” that actually means several times throughout the year. And if you fall into the category of “what if I’ve never pruned ‘em back, can I prune them back by more than half this October?” Yes!!! Oleanders can withstand severe pruning and many mature, established plants have been “rehabilitated” through the use of careful pruning.
Want to know what to feed them? Anything and Everything. In the 23+ years I’ve been sharing this kind of information with you, I’ve found that they will feed on everything from Rose Food to Azalea food to Hibiscus food and anything and everything in-between. Just avoid the ‘super-bloom’ numbered fertilizers, with exceptionally high middle numbers ex: 10-50-10, because like hibiscus and their need to bloom on new wood, we need active green growth more than we ever need high doses of phosphorous (the middle number in the NPK formula) that promotes blooming.