The amount of water added to a room from a pebble tray is so small it does not change the humidity of the room. ... Increasing humidity by 1% or 2% has no significant effect on plants. Pebble trays don't work.

Do humidity trays actually work?

Do Humidity trays really work for humidity? Yes and no. Pebble trays can only do so much to increase the humidity level for indoor plants. The water from the tray is supposed to evaporate up into the air (or at least up into your plant's pot since it's on top of the tray) giving your plants extra moisture.

Do pebble trays attract mosquitoes?

Generally no, the pebble tray should not attract bugs. If you brought the stones from outdoors and see bugs soon after the reason would be the stones not being adequately cleaned before making a humidity tray.