It rather depends on which species of plant
, and what kind of climate you live in.
I have a bunch of yellow flag (iris) growing
in a bed along with an Australian eucalyptus, a Livistona Chinesis, and a bunch of other oddly matched shrubs and grasses.
So how do I water?
Well, I drench the flags morning and night cos they are marsh lovers, and I have a huge virginia creeper and a huge jasminum planted at the back of the bed to soak up the excess water so that the livistona doesn't get drowned.
And, water to replace what they lose through transpiration.
This is really important. Generally speaking, the more foliage a plant
has the more it will transpire, so my virginia creeper is transpiring tons, it soaks up the excess water and stops the other plants
You should never water 'just a little bit' in hot sun (especially over the foliage), if you're going to water then water well. But try planting something that will grow big at the back of each bed to absorb excess water.
You could also consider using lots of crushed perlite to hold onto water in the soil. This stuff will release its water as the soil begins to dry out. Its good stuff.
Hope this helps