You should have no problem trimming the plant/bush to be a bit more compact. They will grow fresh new side shoots. Deadheading will prolong the current bloom cycle. I hope this helps

I planted some of these in a flower pot in late spring. Now it is August and they have filled the flower pot to bursting. I have trimmed them often and take the cuttings in and put them in a vase where they last quite awhile. They are sturdy, pretty flowers and they should last right up to frost.