Hello, Growing a Kumquat here in Colorado. Got it three years ago and so far has grown to almost 4 feet tall. Love the plant and I think I'm doing well. My question is if there is a way to train it to grow more vertically than horizontally (or bushy). I know with most plants if you want more bushy growth you can trim the top but is there a reverse, to get more vertical "tree like" growth? Thanks!