Hi Nancy! Since three of the five are doing nicely, I'm going to assume that you aren't overwatering and that you've already checked that those two containers have adequate drainage, common causes of the 'uglies' on geraniums and petunias
The two containers that aren't doing well may be getting dosed with pool water-are they in the 'splash zone'? The containers may be getting pool water dripped into them, too, if they are placed in an area where swimmer congregate to dry off, queue for the diving board, etc. Or the containers could be getting something dripped into them from an overhanging tree, roof, or other landscape/hardscape feature.
If you can't find the explanation for the failure to thrive in those two containers from the above, the only other thing I can think of is that something in the container is causing the plants to suffer-even if you bought the containers at the same time and all five are identical, it's possible that those two containers came from a different manufacturing lot (or even manufacturer), and something in the coating or materials is not right for plants.
OR it could be the plants themselves-even though petunias and geraniums are considered perennials in most areas, they do have a 'shelf life'. Are the plants in those two containers older than the others? They may simply be running down to the end of their flowering lives.
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