Garden cleanup or “sanitation” at the end of the growing season is a way to reduce some of the plant disease potential for the following season — The list of plant diseases that can overwinter is long, but those that can perhaps be reduced the following season by good fall clean up include rose black spot, hollyhock rust, Septoria leaf blight on Rudbeckia, bacterial blight on geranium, botrytis blight on peony, bacterial leaf spot on English ivy, canker and dieback on vinca, crabapple scab, and Septoria leaf spot on tomato, just to mention a few.
Disease management can include debris clean up, such as raking up infected leaves, flower heads, and other plant parts, and cutting infected stems back close to the ground. The debris can then be put in yard waste for collection or otherwise removed from the garden area. It can also include turning plant debris into the soil or adding it to a “hot” compost pile where it will degrade quickly. Plant pathogens are less likely to survive over winter if organic debris in the garden decomposes quickly.
Weed management can be important as well, as some weeds are hosts for the fungi that infect cultivated plants and most weeds this time of year also have seeds. For example, round-leaf mallow, a common lawn and waste place weed, also serves as a host to the hollyhock rust fungus and can serve as a source of spores (inoculum) the following season. Horse nettle, jimsonweed, and nightshade also serve as a host for the same pathogen that causes Septoria leaf spot on tomato. Tomato rotation without tomatoes but with these weeds, even for four years will not avoid this disease.
Infected plant debris can also be “hot” or fast composted, which involves raising the pile’s temperature so that debris decomposes quickly, killing the plant pathogens and weed seeds. Shredding or chopping plant debris allows more surface area for the decomposing organisms to work on, and will speed up the process. The minimum pile size must be one cubic yard (a three foot cube) and the internal pile temperature must reach and sustain 120°- 160° F for two to three weeks. Making fast compost involves a good mix of green and brown debris initial layering and watering plus turning the pile frequently, keeping it moist (50-60% moisture – moist, but not wet) and making sure enough nitrogen is in the pile to fuel the decomposition process among the microbes. Piling up debris and letting it sit unattended for several months will not kill plant disease organisms or weed seeds, and the compost pile may then actually become a source of inoculum & weeds for the following season.