....is that the soil dries out more quickly than an expanse of ground. Big pots, of course, dry out more slowly than little ones, but the smaller ones can be moved around to get the best design and stuck out of sight when they're out of bloom.
So you can try to keep up with the evaporation or install some sort of watering system, usually less than ideal for some plants, or you can get the most out of a single soaking. How? I do mean soaking. Fill a pail, or a tub, and let each pot sit up to its rim in water for at least a couple hours, even overnight. Both easier and more effective than simply dousing them from a hose. A single soaking lasts much longer.
But... be careful not to overwater. Roots need air and keeping the potting mix sopping wet eliminates that essential element. Do it once and you'll never risk it again. First the leaves turn yellow because they don't have enough water, the roots have rotted off, then the plant dies. A dry plant can often be helped back to health but rotted roots are almost always gone forever.
By the way, the best plants for pots are the really drought-tolerant ones, the plants that might get too much water during our winters. Just stick them under an overhang or in a carport after a freeze, or even once the weather turns rainy, and they'll be happy. That will also protect them from the lowest temperatures as well.