No, you cannot plant a tree above a gas line. Tree roots grow and spread over time and can sometimes dent, crack, or penetrate a gas line. Those same roots may also cause accessibility problems for maintenance or repairs. You can generally plant vegetation with non-invasive root systems, low-growing vegetation, and flower beds near gas lines. 

There are two types of arborists: certified and consulting. A certified arborist is licensed and equipped to provide tree pruning, planting, fertilizing, monitoring, transplanting, treatment, and removal services. A consulting arborist specializes in tree appraisals, diagnosing problems and recommending treatments for illnesses. However, they will not provide these services themselves. Most consulting arborists are certified arborists who can refer you to a tree service that can administer the correct treatments.

Though summer is not ideal, you can do some light pruning during this time of year. Just make sure it’s not excessive. Vigorous pruning will stress the tree and impact next year’s growth. Generally, August to September are the best summer-pruning months, particularly for fruit trees.

Generally speaking, you’ll want to avoid flush cuts, which are cuts made as extremely close to the trunk or main branch. These cuts can weaken your tree, lower its natural defense mechanisms, and even cause decay. You’ll also want to avoid tree topping, which is the total removal of the leader and upper main branches of a tree. 

Most pros will advise against either of these methods, which is why hiring a pro is often the best choice when it comes to tree trimming.