Composting diseased plant material

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By Dennis Morgeson

Now that we have had a killing frost and it is time to put the garden to bed, I have had several questions about composting plant debris with disease infections. Several people have asked me if diseased plant material such as leaves with powdery mildew, black spot, anthracnose, or fire blight should or could be placed into a compost pile and decomposed enough that the disease won’t re-infect next year. And, of course, the answer is that it depends.

In order for your compost pile to kill pathogenic fungi such as black spot, anthracnose and powdery mildew it must reach the magic temperature of at least 130 degrees for at least three consecutive days, and now you are wondering how you can tell. Well, you can get a composting thermometer or you can simply take your chances.

One thing to keep in mind is that your compost needs to be turned periodically to allow oxygen in and to keep a fresh supply of food for the bacteria to feed on, which in return will cause the pile to heat up.  There is a way to put your pile together to increase your chances of having healthy compost, without a bad smell, and one that will get hot enough to kill fungus. Believe it or not, a good compost pile actually takes work and preparation.

Before placing anything on your compost pile, acquire a good pile of dry ingredients such as dried grass clippings, fall leaves, perennial plant stalks, or whatever. You will also need a pile of green or wet ingredients. These should be layered alternately in 4” or so increments.

You can also add a little nitrogen in the form of manure or fertilizer to get the process to go a little faster. Now, don’t add anything else to the pile. Turn it every week or so and it will soon be compost.

One other thing that will help speed the process up is to mash any large stalks, etc., or run the entire “mess” through a chipper shredder. Smaller pieces increase the surface area for the bacteria to feed on and decompose faster.

Now, if you have fire blight infested plant debris and you want to put it in the compost pile, don’t use that compost around things that are susceptible to it. The infecting agent with fire blight is bacteria and they may or may not be killed in the compost pile.

Any plant debris such as limbs that you prune out that are infected with fire blight should be burned to insure the bacteria get destroyed. You know, fruit wood smells really good burning in a fireplace!

If your compost is like mine and things get added to it over time and it really never gets hot, it’s easier to pile a bunch of stuff on it for a few seasons and leave it.

Start a new compost pile and use the compost from the first pile when it is ready. This way it takes several years for compost to be made and it gives you enough time that the disease organisms are killed over time slowly during decomposition. I call this easy or lazy compost making. But remember, this compost will have weed, flower, and vegetable seeds in it that will come up anywhere the compost is applied.

Most people don’t worry about what they put into their compost piles and many times they don’t have any real problems, however, there is an increased chance of problems if you put diseased material in a pile and use it during the first year if it doesn’t reach the magic temperature of 130 degrees.

To help control diseases, you should be selecting cultivars of plants that are resistant. This in turn will decrease the amount of infected material that goes into the compost pile, which in turn will decrease infections.

That to me is a sustainable approach to composting that is easy and effective!

Happy gardening!