The answer to ‘can you’ is yes. You can harvest marijuana without flushing it. However, the answer to ‘should you’ harvest marijuana without flushing it is a strict no. Flushing your weed is very important no matter what purpose you are growing it for - if you are growing it for a medicinal purpose then it is doubly important for you to flush it and if you are growing marijuana for consuming it for recreational purposes, then too, you must flush your weed before you harvest it so that all the excesses are drained off.