planting over a large tray of water (do not put the pots in water) will increase the humidity around the trees.

as for dormancy the trees will have to be kept below 40F for 40+ days. my concern is here in the temperate zone sunlight reduces greatly as winter approaches this plus the lowering temperature signals the trees to drop leaves. if your climate supports these factors I think with some extra summertime care you will be fine

Just by watering, there is not much else you can do in the open. But it will not do any harm, where I am the humidity varies I take no notice of it.