After a failed attempt to grow mint from seed, I purchased a spearmint plant, replanted it into a larger container, and placed it outside in full sun, as the instructions indicated. In the few months it's been outside, I've noticed that its appearance has changed: the leaves have become smaller and it has started to put out more horizontal runners. It doesn't have the full, "bushy" look it originally did. I'd like to harvest leaves for tea and other uses - is there a way I can encourage it to produce larger leaves? Does it need pruning? If so, how should it be pruned to maximize fuller leaf growth? Any other tips would be appreciated.