I was talking to a friend about the concept of air pruning as a way to keep grasses out of beds. It seems to me that if I edge my beds with a "Cambridge edge" - a mini trench of, say four to six inches between the bed and the lawn, that it keeps the grass out really well, effective until that trench filled in. I seem to remember when I lived in quack grass country that it worked for it, too. Am I imagining this, or does the concept of air root pruning work for quack management in your experience?