Can someone please tell me why the leaves are curling?

This can be caused by a variety of things. Virus, fungus, mineral or nutrient deficiency, or insect nibbling can all be to blame. ... They suck on the undersides of the leaves, causing them to surl as the juices are removed from the leaf.

Could it be that you have the mulch too close to your plants and this is causing critters to bed in there? Usually mulch should be at least 3 inches away from the base of plants.

Do you have a peach tree ? If so,it is infected with a fungus,& spreads to other foliage. Tough to get rid of. Use a copper spray on both. However, with tree, wait till fall, when there is no foliage, then spray,...do same in spring.

If you are not seeing any evidence of pests (aphids, spider mites, thrips, etc.) then fungus is a possibility. Another answer may be over-watering. If you've gotten a lot of rain, the leaves will overload with water and start to curl.