My pots have great drainage and I only water if it has not rained for a week. During the summer you will see irises with brown tips on the foliage. This is because they are not getting enough water. If I see a tiny brown tip.... I soak them. After bloom season, people mow irises down, they trim them into fans or trim the brown tips.... all because they say that irises look so bad in the garden. I think this is why the custom of trimming irises into fans during the summer became a practice for years. It was a way of covering up drought stress. Irises are drought tolerant. But that does not mean that going without water does not stress them. However, that being said, I live in a hot summer climate and don't have a clue how to grow anything in New England.
If it is cooler there and if you have more moisture you may not need to water as frequently. The only thing I would do is keep the drainage holes open and watch for stress such as limp leaves or brown tips.
And good luck!
