Experts and BHG readers answer.
Leaves in flowerbeds
Tree leaves should not spread disease problems to your flowering perennials, but if they are thick enough on the beds to pack down, they could smother the perennials or keep them so wet that the perennials could develop rot. If the old perennial plant foliage is part of the mix, there could be disease spores on the old leaves of the perennials. It's safest to clean out the beds and compost the material before reapplying it to the beds.