Many tree care activities can be carried out all year long. For other activities there is a season. Spring and summer are the best opportunities to identify tree health problems. A quick inspection can tell whether the tree “looks” healthy compared to previous years or nearby trees of the same species. Diagnosis of the actual cause of the tree problem normally requires an expert. Should you feel your tree might be unhealthy, have it inspected by an arborist. Prompt detection and treatment can be critical.
Most pest management activities have a very specific and narrow window of treatment that coincides with when the pest is active on the plant and/or vulnerable to the treatment. Fertilizers are best applied when the plant roots can actively uptake the nutrients.
Generally, pruning can take place throughout the year, but there are some exceptions to this rule. There are a few trees susceptible to insect and disease problems that could be encouraged if pruning is done at the wrong time. Check the literature on your tree species and/or call your arborist.