Hi Nigel. The category you are looking for is Service a la Personne. You are not a gardener because this falls under farming. You'll be allowed (last time I looked) to help out at other people's houses under the S a la P category. Strimming is allowed, but you can't plant anything or cut anything. You aren't even allowed to cut grass, as this is strictly farming. You are, however, allowed to tend to lawns. At least, last time I looked. But there have been a lot of Thursdays since then and anything you want to do will change, in my experience, every second Thursday.
Good luck with everything.