I know I'm a little late to this, but the enchanted shears work ok on a garden bed (they gather the resources fine) with the only "missing" feature is the ability to also remove the plant from the bed. That creates additional clicks that is not needed. They should have made it like mining for granite where you single click the shears and have a option to "prune plant". That would have made them great. When I do grow plants and use the shears, I just use the "Last Object" macro for the shears and click all 9 plants in the bed... it takes less than 15 seconds.
Thanks
@Poo for the suggestion on using UOA for the harvesting. I don't do plants very much these days but will be a nice option if I decide to ever use all 6 beds I have all at once again.