Help needed claiming deductions from DPS

Tenancy Deposits

Hi. I have a tenant who is moving out in 2 weeks. They've contacted DPS already and are requesting their full deposit to be returned.

On the DPS site when I click disagree the claim boxes appear showing-
Reason for deductions... let's say gardening as an example
Amount to be claimed...
Description (500 characters)...

So, the photos I have on their move in day show a lovely garden with neatly mowed lawn, nice borders, clipped hedges etc. It's now a jungle and will take a whole heap of work to get it back to its former glory. (Of course they said they loved gardening when I showed them the house!).

I plan to give the gardening job to my father in law as he's retired and pay him say £20 an hour casual labour. If it takes 30 hours to get it right then will DPS adjudicator accept £600 as the cost?

Thanks in advance... Ray