Keep your container garden happy and thriving on long hot days by installing a hidden water reservoir. All you need is an empty plastic bottle around the same height as your planter. It will be easier to start with a new planting than an established container.
Cut. Using a craft knife, cut the bottom off a plastic bottle. The cut bottle should be no taller than the distance from the bottom of the pot to the top of the soil line. Remove the cap.
Place. Fill your container up partially with soil, and then place the empty bottle, upside down, in the center. Add more soil around the sides so that it stands up.
Plant. Add your new plants in the donut shape around the bottle.
Water. On hot days, just fill up the bottle with water, and it will slowly trickle down to the deep roots of your plants. You may still need to top-water at first while your little plants are getting established.
As the plants grow, the bottle will become harder and harder to see, but you should still be able to easily fill it up as needed.
If you're worried about mosquitos, just be careful not to over-water and you shouldn't have any problems. Here in the midwest, even reservoirs made from 2-liter bottles dry out every day all summer long. Using the bottle upside down makes it easy to add water; if you would like to use a bottle cap-side-up instead (with drainage holes cut into the bottom to let the water out into the soil) you will need to be more precise when aiming your water stream to get it in the small bottle opening. And you will need to be even more careful not to over-water, as the trapped space will get very warm and potentially fetid.