No excuse is necessary, as you owned it. If he owned it, you owe compensation. Ownership is by where the trunk is. If you shared the boundary tree, you will owe half as compensation; the excuse would be it was a nuisance and potential hazard to your property (the garden). Lawyers agree that certain basic legal tenets will apply in any state. For example, the ownership is normally determined by the trunk. If it is clearly inside a property line then the tree belongs to the owner of that property regardless of how heavily its limbs hang over the neighbor's land. Problems caused by the overhang will be covered by local laws governing private nuisances. It will mean, for example, that the neighbor has the right to trim any overhanging branches whenever they interfere with an activity -- provided he can do the job from his side of the property line. If he needs to go onto the tree owner's land he must first get the owner's permission. And a professional tree surgeon handling the trimming should be reminded of this. Many automatically seek such permssion. The right to trim trespassing branches is so ingrained in law that failure to take action to preserve one's property in the face of a threat can absolve the tree owner of liability. In the 1985 case of Loggia v. Grobe, a homeowner in Centereach, L.I., could not recover $1,500 in damages after his concrete patio had been ruined by the roots of a neighbor's tree. The Suffolk County judge ruled he was not eligible for damages since he had failed to take any prudent steps to protect his patio after the threat became apparent.