Property is in Maryland. What action can be taken under the law to cause the otherwise healthy tree to have the deadwood removed so it does not harm my garden?
This is another common real property question. There is a reported case decision that say you may cut or trim any part of that tree which extends over your property line. Of course, working in tandem with your neighbor may promote a better relationship, but you can take unilateral steps to protect your own property. But any action on his side of the line would require permission, or even a court order that he abate a nuisance.