Always boil soilless mediums or bake soil. If you have smaller plants in little pots, you can wrap the pot in panty hose liners all the around the pot and stalk with a twisty tie, and still be able to water through it. They can't fly in or out, and even the drain holes too. Bigger pots and you might need to cut and fasten the liner on, including the drainage holes, could get tricky.
You can sprinkle some mosquito bits on the top layer, and also steep your water with them or the dunks too, helps kill the larva.
