Evan, I will quote my response from PWRA, if any others would like to add to the discussion here as well.
Not a bad idea, but you definitely should take some time to learn the landscaping market in your area, if you haven’t already done so. There is a big difference in lawn service and landscaping as well. Most areas are saturated with grass cutters, and margins are slim. To be a licensed landscaper (not just grass cutter), at least in my area, you also need to be a horticulturist with knowledge of landscaping blueprints and local flora, fauna, and their applications.
You would be spreading yourself thin, because you would also have to run a separate crew, or dedicate days to haul your landscaping trailer… which would take away time from your other business. Please don’t forget the additional insurance, and licenses this would require.
I hope I am not discouraging you, but these are the realities I have already dealt with.
If you really want to try it, then this time of year may be a good time… grass cutting slows down significantly, you could focus on fall cleanup, and work your way into the busy season. You can also look into tree cutting, and pesticide/herbicide applicators license to spray roundup/weed control. All of these require licenses, and insurance coverage of course.
I think the more services you offer, the more work you have available to you, but sometimes the risk/reward just isn’t favorable. Some customers are not just looking for someone to cut their grass, they will want full landscaping. It may be easier, and more beneficial for you to get familiar with a landscaping company in your area, and build a business relationship in which you refer each other work… or it has been discussed here many times to offer your time to work for free to learn the business. Good luck brother, I wish you the best if you decide to add these services.