I'd suggest you mention it to the landlord, who will most likely be delighted you are tending to the garden. Chances are, if there is no growth at this stage of the year, it is dead....loads of plants died off this winter. But some are only just coming back.
I had a fab fuschia in a rented property & the tenant dug it up 'cos she didn't like it (springtime & it looked about miserable). It had been there for about 20 years & was magnificant in the summer.
I'm generally OK to let tenants do what they want within reason. What I don;t want is something that will add extra maintenance for me when they move on (one tenant decided to paint the "caps oin the wall & pillars - yes, it looked lovely when it was first done, but I now have to redo it every couple of years).
I had one great girl & her mother moved over and the garden was stunning when she left. She even used to bake me cakes !!! Chances are the landlord will be thrilled.