What is the best fertilizer for the bougainvillea?
I think the control release fertilizers like osmocote are the easiest and best way to give container plants optimal fertilizing. Your garden centres should have some selection of these…usually spherical granules that can be mixed into the soil when repotting…which you probably want to do each spring. The one other thing is micronutrients…I use micromax, which works very well with osmocote…but other brands might be available where you are. A control release with all the trace elements would be most convenient if you only have a few pots to feed…I’m not sure such a thing exists but would hope so for your situation.
