Supposed to? No. Can you? Yes, you can at any time. Should you? It's in the eye of the owner/grower. It would probably make it look better and encourage more growth but not necessary.

Thank you for taking ur time to respond to my question.

I have another one for u as I see u enjoy container gardening. Can u recommend a tree for container planting in so cal zone 8?

I am wondering if you're asking about the need to deadhead tuberous begonias. These have pretty big flowers and as they die if they don't fall off away from the plant, I am thinking they should be taken off so as not to cause any fungus to the plant itself.

Good point maryjozone5!

janruiz, I don't know enough about S. CA. to give any good advice on planting a tree in a container. I'd say your best bet would be a dwarf Japanese maple though for almost any climate. You could check other forums for bonsai trees.