Answer: Both your snapdragons and glads sound as though they have developed fungal diseases. Mostly these are caused by growing conditions and by getting the foliage wet when watering. You can try a fungicide but the snaps will probably not recover. Pull them from the garden and destroy them; the glads need to be cleaned up in the fall so none of the old leaves remain in the garden. Next year they should be fine.
Peonies can fail to bloom if they don't get enough sunshine, water, or if they are planted too deeply. If your peonies bloomed last year but not this year, depth is not the problem, but growing conditions probably are. Just continue to care for them and next year they should bloom for you. Likewise for the irises.
Some years just aren't all that great for growing beautiful plants. Sounds like this year is not a good one in your garden. Next year should be!
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