Question
We live in an older home with extensive low stone wall hardscape. Recently we lost a large elm to a windstorm. It was (or grew as a volunteer) with in 3 feet of the edge of a low (15 inch) retaining wall with some brick patio stones surrounding it. I had noticed prior to losing the tree that it had pushed up some of the patio stones, and also that there were also some stones almost imbedded in the base of the tree! We need to replace the tree, as we need the shade and privacy, however I obviously need something that will be ok within the boundaries of the bed. I will remove as many of the stones as I need to. I think I can get the bed as large as 25 ft wide and completely open in the back, fronted only by the low wall that cannot be removed. It gets full to partial sun, mostly morning. I read your recent posting about small root crowns. I would prefer deciduous if possible. Any suggestions?


Answer
Since you did not make it clear where you live it is hard to make a species suggestion. However, I will make a few comments that might help. One, you could use a root barrier. See www.deeproot.com for some ideas and call them to find a local distributor if you want to go that route. Two, a tree with small leaves and little or no fruit or seed drop issues is good for using near patios. Small leaves can often go un-raked in fall and no fruit/seed means no mess on your patio. This is why Elm is good. Chinese elm may be good if it grows in your zone. Also when selecting a tree consider the leaf density. Many maples are fast and stay relatively small but are very densely leafed and allow little light to penetrate. Oaks are typically more open but slow growing so you may want to select a larger one to start. With oaks you need to look for the ones that have little or no acorn drop. Also you can consider larger versions of understory trees. Trees like dogwood, redbud, etc. Or flowering trees like Crapemyrtle.
All the larger variety deciduous (elm, maple, oak) trees will need to be planted at least 6 feet from any significant slab, wall or structure if you truly want it never to be a problem, that is unless you use a root barrier, but even then 3 feet would be a minimum.

best of Luck
Sean Murphy, ISA, RLA
www.seengineering.com