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Compost Q & A With a Master Composter, Part 2

This week we are tackling a few more questions in our Compost Q & A series, with Master Composter, Sarah Ferry. Here are some more great questions from Simple Organic readers, taking a look at topics like bacteria in compost piles, paper products, and looking at the issue of composting pet waste, which we touched on once before.

Simple Organic: I always thought that you could compost anything from your garden. But then a farmer in our area told us never to compost tomato plants. He said that our humongous pile of composting material we now can’t use on our garden because of the bacteria that tomato plants can grow. Is that true?

Sarah Ferry: This is an area of debate, but essentially you can add many things to a compost pile if the pile is properly managed and gets hot enough (to at least 150 degrees). When the pile becomes hot throughout, the heat kills the pathogens that are present.

However, most backyard composting systems do not regularly reach this level of heat to kill every pathogen in the diseased plant so if a plant in question carries disease (such as tomato plants), it is always best to leave it out. If you can be certain that you can maintain a temperature of 150 degrees throughout the pile the heat should kill most pathogens but it is best to err on the side of caution if you are not sure your pile is reaching this temperature regularly (it is a great idea to invest in a compost thermometer to see how hot your pile is getting!).

SO: I’m curious about paper products. We garden organically and I’m always a little reluctant to put shredded paper in the compost because so many papers and inks are treated with nasty stuff. Any suggestions on what’s safe for organic veggie garden mulch and what’s not?

SF: This is really a personal call. If you are serious about being purely organic then you may want to forgo the dyed paper and ink to “certify” your land as purely organic.

In my opinion, however, the little bit of inks and dyes are not harmful enough to effect the quality of produce especially once the pile becomes hot enough to really break things down. If you are using the paper in a worm bin this is especially the case.

Photo by kirybabe

My personal belief on this issue is that in composting the paper, you are being far more environmentally sustainable than shipping it away to be recycled which uses far more fossil fuels and energy than we would want. I like to close the loop as close to home as possible. Stick to the regular or newspaper type paper, and leave out the glossy stuff.

If you are really worried about the organic integrity of your garden, but would like to reduce the impact on the environment- you may want to consider adding a worm bin to let the worms digest this paper (they love it!) and use the worm tea on your ornamentals.

SO: In my research I learned that you CAN compost dog waste with the worms, but you should not add food items, only the “bedding” and dry matter. Any thoughts on this?

SF: Ok, you got me– If you are really serious about it, you can compost dog waste- but you would not want to mix this in to your normal compost bin that you are using for other items. You also would not want to put this finished compost on your garden (perhaps just your lawn or ornamentals), unless you are getting them sufficiently and consistently hot enough to kill all pathogens.

It would be a lot of effort to run a separate pile just for this purpose unless you are really serious about working with your dog’s poo– and if you are I do not mean to stop you– but if you are only managing one pile and want to add food scraps and use it on your garden then I would leave the dog poo out.

Have these questions and answers been helpful to you? We’ve still got a few more interesting issues in composting to look at, at the end of April. If you have any questions that we haven’t answered yet, feel free to ask them in the comments.

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  1. Sarah M

    Love this topic! I have a couple more questions to add: 1) how do you know if your composter is “hot enough”. We have a big covered black bin we bought through the county. I have put all sorts of garden waste in there. You mentioned with tomato plants it needs to get hot enough. What is that temperature and how do I take it? 2) How long does compost need to sit before you use it? We put all our organic kitchen waste and garden scraps in there last year. Can I till that compost into the soil this spring? What is the typical “waiting period”?

    • Kara

      Great questions. I’d like know many of these as well.

      • sarah

        Excellent questions! The ideal temperature for compost to thrive is between 100 and 140 degrees. If there are known diseases in the pile I would try to get it on the hotter side to make sure to kill them- but compost breaks down most efficiently between 100 and 140 degrees. you can tell if your pile is hot enough if you see a bit of steam come out of the pile when you go in and turn it. It will also be warm to the touch if you take a handful. The most precise way to tell if it is hot enough (and if you re trying to kill any suspected disease in the pile I would recommend being precise) then you can buy a compost thermometer. I find this tool very handy and fun to watch when your compost is hot!
        As far as the waiting period goes if you have an active compost pile it is good to let it sit for a couple months to “cool down” before tilling it into the soil and planting. Compost is full of organisms that break things down so you don’t want to put living and active compost on your new seeds you just planted! I typically start a new pile when I am waiting for my first pile to “cool down” for a couple months- so I can continue to recycle food scraps during that time. Turning towards a worm bin during that time would be a good solution also!

  2. renee @ FIMBY

    I love composting! There is just something so satisfying about nature’s own recycling. I compost all year round in a cold climate. During the winter the pile just builds up and then in spring quickly composts with the extra sun and moisture from melting snow.

    I compost our pine pellets cat litter but not the actual poop, that goes in the toilet. I compost tissues (from nose blowing, we don’t use cloth all the time), paper napkins when we have large groups of people and I don’t use our cloth napkins and of course all our vegetable and fruit scraps – of which there is much in our mostly vegan kitchen.

    I’ve had diseased tomatoes so I have to burn or throw away those plant parts. I also have lead in our old eastern US city soil so I can’t compost leafy plants from that soil (nor can we eat them).

    I’ve blogged about that whole composting process here:

    I realize most people don’t have to deal with this but if you are an eastern US urban gardener (soil contaminated from old lead paint and building materials) you need to have your soil tested for lead.

  3. Jay

    I keep hearing a different level of heat required as low as 140 and as high as 180 for composting to destroy any pathogens to make it safe for general use. Between my own and my fosters, I currently have 9 large breed dogs with all the associated waste build up. It’s too much flush or put into the garbage bin. Composting this much would not keep up with the supply so to speak.

    The question is this. Would drying out the feces and burning it produce a safe and usable fertilizer for food gardens? I have run a small test where I mixed in the ash and re-seeded a grass area that has grown in nicely. Can this be scaled up and used to create a safe and quality fertilizer for any use? Any ideas?

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