There are mosquito disk things you can put into the water, to kill off the mosquito larvae.
Ditto on keep the crowns out of the water, and maybe change the water. Depending on how hot it is/will be where you are, you may also want to keep those tubs of water in the shade. Ask me how I know.
Oh - and you will want to be wary of losing the labels off your plants, or else the writing off the labels on your plants, while they are sitting in tubs for two months. Ask me how I know
that, too!
The fix there is to make your own labels and wire them firmly onto the plants, otherwise keep only one cultivar per tub - and make sure you know which tub is which!
