Tree trimming professionals - Ask Extension
Hello,
We are first-time homeowners and have been advised to get a couple trees on our property trimmed to avoid roof/gutter damage. I'm primarily ...
Knowledgebase
Tree trimming professionals #925143
Asked February 27, 2026, 11:56 AM EST
Hello,
We are first-time homeowners and have been advised to get a couple trees on our property trimmed to avoid roof/gutter damage. I'm primarily concerned about the health of the trees (and the wildlife that depends on it) and want to make sure any tree trimming professional we hire follows best practices for the health of the tree. Is there a certification program, or something we can look out for when hiring a professional tree service? And what time of year is best?
Prince George's County Maryland
Expert Response
Yes, arborists are certified through the International Society of Arboriculture (ISA), and you can look for ISA-certified arborists on the linked page. Maryland also requires that tree work (for hire) be done by licensed tree experts (who pass a comparable qualifying exam). Our understanding is that such exams are pass-fail, so an individual might not do as well on the tree biology portion and do best on the safety portion, so professional arborists can still vary a bit in their level of expertise and experience. Looking for a consulting arborist might be one way to avoid using a person employed by a particular tree care company, if you prefer that they're as impartial as possible with the regards to the potential they will recommend an expensive procedure that might not be necessary or able to improve tree health for very long. Any arborists should be able to diagnose issues (or at least narrow-down likely causes of a tree's current condition, as sometimes advanced or chronic damage is hard to trace back to a particular trigger) but be aware that they can't always treat or cure every ailment they may find. If a tree is in decline, it's not uncommon for the causes of that decline to have affected the tree well before -- sometimes years before -- symptoms became obvious.
Arborists can speak to what time of year is easiest for them regarding diagnostics, but branching structure is easiest to see in winter (for deciduous trees), and canopy vigor is easiest to see in spring/summer once the leaves have fully expanded. As for the timing of pruning, that will depend on the species of tree and the reason for pruning. Removing damaged or dying wood is generally done any time of year so it doesn't worsen and risk injuring healthy wood, but cutting off branches causing specific problems may best wait until a certain season so the pruning cut is at a lower risk of wood decay infection. You can look over the Virginia Tech tree pruning calendar as an example, though we defer to arborist experience and advanced training if they suggest different timing for certain situations.
Miri
Arborists can speak to what time of year is easiest for them regarding diagnostics, but branching structure is easiest to see in winter (for deciduous trees), and canopy vigor is easiest to see in spring/summer once the leaves have fully expanded. As for the timing of pruning, that will depend on the species of tree and the reason for pruning. Removing damaged or dying wood is generally done any time of year so it doesn't worsen and risk injuring healthy wood, but cutting off branches causing specific problems may best wait until a certain season so the pruning cut is at a lower risk of wood decay infection. You can look over the Virginia Tech tree pruning calendar as an example, though we defer to arborist experience and advanced training if they suggest different timing for certain situations.
Miri
