they refuse to make a recommendation.

I have locks on my gates to my 6' wooden fence. It is very low tech, simply padlocks, one is combination, one is key.

To decide what to use, I would think about how often you will need to open the gates, if people other than yourself will need to open the gates if you are not home and your weather i.e. will the lock often be frozen due to moisture in freezing weather.

Not sure how often your gardener comes but when I have lawn treatments once a month I take a risk and unlock the gate in the morning then lock it when I get home from work. I use the locks for security also since most of the breakins around me happen in the back. A keypad would probably work in your climate and if you have the same gardener all the time, that would be easy for them to use. However, if it's a company and you never know who is coming to your house, I wouldn't want to use a keypad, as the number could get passed around. I'd rather risk leaving it open occasionally.

Padlock, with a spare key to the gardener if you trust them.

does anyone have a brand to recommend?

Mine are Master Lock https://www.masterlock.com/products/home-personal-property?personal. There are so many options, combination locks, key locks, padlocks, etc. and differing lengths of shackles. I see they even have biometric and bluetooth now. That might be interesting.

I mount mine on the inside since it's just for family to go out once we're in the yard (and I write the combination on the inside of the wooden fence so no one forgets but it can't be seen from the outside).

When my neighbor tends to my plants if we're away, I put a padlock with a long shackle on the outside so it's easy for her to manipulate.

Pamela - Did you find anything? I am looking for the same thing for my pool guy and gardenr in So Cal.