Answer: Mushrooms grow in moist areas and in general are no cause for worry. When they're associated with trees and tree roots, they can indicate that the trees are beginning to decay. In your perennial beds, you might try removing any mulch, at least for a while, to let the area dry out some. That will probably take care of things. I'm not sure what you mean by "too late" for your verbena. Have the plants died? Verbenas suffer in poorly-drained soils, and can succumb to disease during unusually damp weather. The mushrooms you see indicate moist conditions, but this type of fungi doesn't affect your perennial plants directly.
To help control disease problems, be sure to space plants generously, to allow for good air circulation. And make sure the area is well-drained; if it isn't, try incorporating lots of organic matter into the soil and/or create raised beds. Your tulips should be fine--as long as the soil isn't too wet.
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