Whose responsibility is it to cut the grass?

This depends on the individual tenancy and should be covered in the lease agreement.

Some landlords will maintain the gardens themselves as it gives them an opportunity to keep an eye on the property. Others will supply a lawnmower for the tenants to cut the grass.

Whichever option you choose make sure it is clearly outlined in the lease agreement and pointed out to the tenants at the beginning of the tenancy.