How to have 2 separate tenants share lawn maintenance?

[Natalya Murphy]

We own a mixed-use building with 2 commercial tenants on the bottom floor and 2 apartments on the top floor.   The building has a total of 4 separate addresses and has a small lawn behind it that's used by all the tenants.

I'm in the process of revising the commercial leases and would like the 2 commercial tenants to share responsibility for the maintenance of the lawn.    When I lived in town it was easy to handle this maintenance myself, but now that I live over 1,000 miles away, I'd rather hand over the responsibility to them.   It would also make it easier to ensure that the work actually gets done.  It's a tiny area (about 15' x 15') so finding a landscaper willing to do the work is difficult.

Ideally I would like the tenants to all be able to share the area and somehow share the maintenance of the lawn.   If I put just one tenant or the other in charge of the lawn, I see them wanting to become territorial about it.

Any suggestions on how this could be done?