Here in the San Francisco suburbs I keep my lovely, HUGE banana tree in the ground all winter. I'm wondering how far I can cut it down this fall and safely leave it in the ground? We've never cut it back, but it's only April and already 10' or more. It should be OK this year, but at the rate it's going it may close in on the power lines above. We consistently get a few frosts every winter. There is no way I could dig up Jumbo & store it somewhere. Going forward, how can we keep this beauty a little shorter next year?