A great question came in this week to Ask Gardenerd: "It's Yvette from Mar Vista!!! I have a BURNING QUESTION!!! We have a big big rainbow eucalyptus tree in our front yard that is causing big, big problems with our raised beds...the roots (mostly small tangly ones) keep invading and stealing all the water and nutrients from them and we had a horrible harvest...we want to put in a root barrier but we don't know anything about it. Might you…