My starfruit trees love to produce flowers but never seem to set. I grafted them years ago to Kari and Sri Kembangan but they never set. They're in relatively large containers (probably 30 gallon) and grow nicely and flower nicely but never set fruit. I've tried giving them various nutrients, including withholding nitrogen, but it hasn't worked. I've also crudely tried to hand pollinate, but that hasn't gotten them to set.
Is there a trick to getting them to fruit? A time of day to pollinate? What stage of flower should I pollinate at, if any?
I know usually people don't hand pollinate, so I'm wondering what might be wrong here.