As a landlord, i have ceded control of my property (for the most part) to my tenant. If I need to do any work on the property, inside or out. I give them at least 24 hours notice. (Unless there is an emergency, such as a water or fire damage. )
If you are maintaining, a regularly scheduled day of the week should be negotiated, so that you do not have to do paperwork every time.
If tenant values their privacy so much that they don't want you to maintain the yard with proper notice, then they should agree to do the yard work themselves. They do not have a right to allow the landscape to go to waste.