Those irises types that can bloom more than once, such as certain bearded iris varieties, will benefit from deadheading. Ensuring to remove spent flower stalks quickly will give the most time to bloom again and a feed with fertilizer that is low in nitrogen around a month after the first flush of flowers will further increase the chances of a second bloom.
Irises are heavy feeders so they will need lots of water as well as the feed to have the energy to bloom again. One example of a fertilizer that is suited to a summer iris feed is the Dr. Earth Plant Food available at Walmart.