Yes, You Can Compost Diseased Leaves
One hears the strangest things out of the mouth of “experts” sometimes. One of the stupidest is that you must never recycle diseased leaves, such as those with tar spot, powdery mildew or apple scab, for use in compost or in mulch. They insist you must either burn infested leaves or bag them and put them out on the street so the municipality can pick them up and destroy them.
Now this seems to make sense. By destroying leaves bearing the spores of a disease rather than recycling them as mulch or compost, which doesn’t always do the job, won’t you help control the disease? Actually, there is no proof that this makes one iota of difference.
For leaf diseases already present throughout a region, the horse is already out of the barn, so to speak. The disease is out there and unless you destroy every single infested leaf (which is nigh to impossible), you will never be able to control it. It only takes one spore-bearing leaf to infect a hundred plants… and no cleanup campaign will ever get every single leaf throughout a region. Having big trucks haul the leaves away for burning is simply polluting the air for nothing. When I hear the same town recommend, as mine does, recycling leaves on the one hand and not including diseased leaves in compost or mulch on the other, I always imagine the poor gardener, sitting on the ground sorting through thousands of leaves one by one!
This reminds me of the old belief that you had to burn the leaves and stems of mildewed phlox and bee balm (Monarda) each fall to prevent the disease from returning. I did this faithfully year after year and the disease can back every time. I even set one phlox plant ablaze one fall to see if that would work. The plant came back the next spring, but was as diseased as all the others by fall. I eventually found a technique that did work: I removed the disease-susceptible plants and replaced them with disease-resistant varieties. Problem solved!
Let’s get real! WIth wide-spread leaf diseases, the damage is already done. So why not use the affected leaves ecologically by recycling them as compost or mulch? Mother Nature has been doing this for millions of years: don’t you think she knows best?