Dear Rich Staff is fascinated by gardening magazines. Oh wait, it's for that kind of grass!
Other trademarks. Our search at the USPTO website uncovered this trademark: Grass Roots Publishing registered for bimonthly magazines (They're the publishers of I Love Cats Magazine). Because it costs about $300 to file a federal trademark application, your attorney might counsel that you're risking the money because the marks are near-identical (both companies would disclaim "magazine" and "publishing") and you're seeking registration in the same class. On the other hand, it's possible -- assuming you're willing to go through a legal wrestling match with the USPTO -- that you might succeed with the registration. You would argue that Grass Roots Publishing doesn't publish a magazine called Grass Roots, so arguably consumers are less likely to be confused by your use (as a magazine title) and the other company's use (as the title of a publishing company). Also, you might argue that although the potential audience for those who like cats and grass may overlap, consumers are sophisticated enough to tell the difference.
Is it best to use an attorney to file? That depends. For applicants who don't anticipate a problem, it's a fairly easy task using the USPTO's TEAS service (or if you need a little more hand-holding, using a service like the one offered by Nolo). Of course, if you can afford it, it's worth using an attorney. It's essential in cases where you anticipate serious opposition to the registration because preparing a response is usually beyond a non-lawyer's abilities. (Your case appears to be one of those.)
Can we proceed with the name without registering it? Yes, and many companies do just that. It's called a common-law trademark. It's true that registration provides a lot of benefits for stopping others but common law trademarks have worked just fine for thousands of businesses. The neat thing about any trademark is that generally, the longer you use yours, the stronger it becomes (and the less vulnerable it is to attack). BTW, your common-law rights would not prevent the 'other' "Grass Roots" from coming after you at a later date. But, the longer you co-exist without dispute, the harder it becomes to stop your use.