Let's take the two plants separately. First, tulips, over time tend to stop blooming. Unless they are Species tulips, you might as well dig them up and start over. Most standard varieties of tulips are only good for two years and then they slow up. You'll often get foliage, but no flowers.
Iris are another story. They should keep blooming every year, but they also slow down if they are too crowded. Iris require dividing every three to five years to break them into smaller platns. If you don't do this, the plants will crowd itself to the point where it survives, but doesn't bloom. They also need full sun to flower. I would suggest, if your iris have been in the same spot for four or more years, to take a sharp spade, and dig up the clump and break it into smaller pieces and replant them. The best time to do this is late summer/early fall.
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