Many landscapers use way too much mulch around
trees. They often make a donut around the
tree with 6 or more inches of mulch. It looks nice, but it's really not a good practice because water can't easily penetrate through the mulch into the ground where the roots need it. Perhaps you should remove some of the mulch and use it elsewhere. You probably shouldn't have more than 3 inches of mulch. This is usually enough to discourage
weeds while allowing water to reach the roots, plus it should allow you to
plant your annuals directly in the dirt. It isn't recommended to
plant them in mulch because they won't get the necessary nutrients they need to thrive.