Is Mike McGrath correct when he says vegetable scraps shouldn't be added to compost?

Question

I'm composting for the first time this year, in a back-yard composter. I have some leaves in there, and I regularly throw in my coffee grounds. I also occasionally throw in vegetable and fruit scraps.

When I look online (websites, TED talks, etc.) it seems that people often say that it's "okay" to put in vegetable and fruit pieces, but then they act like it's not going to do much for you in terms of end-of-process compost. The common thing said here is "the only thing worth mixing from your kitchen with your leaves is coffee".

However, fruit and vegetable pieces have a C:N ratio of somewhere between 25:1-35:1 it seems, which is almost perfect with the 30:1 ratio that people say is ideal. So from this information alone, one might guess that fruit/vegetables are actually really good for your compost pile, not just tolerable.

So which is it? Are they good or are they merely okay. And why?

Answer 1

Everything that you can eat or is a discard from what you eat (vegetable/fruit) can go into the compost heap. It's what worms eat. And it's way more than OK so long as it doesn't make the heap so wet it goes anaerobic.

The important parts are getting the CN ratio correct so that bacteria thrive, and having the contents just moist enough that aerobic bacteria and fungi thrive. The bacteria require nitrogen as part of their lifecycle, and the fungi break down cellulose and lignins (woody high carbon (brown matter)) so that the bacteria can then process it.

All organic matter from green rose clippings to tea bags is grist for the heap, once you have it properly going with a healthy bacterial/fungal environment, it will break down anything, including accidental included small pieces of ground cloth you originally put down for weed control.

Your major worries should be not getting unwanted seeds into the heap, grass seeds, spearmint seeds, dandelion seeds and anything else you don't want to propagate, so all input materials need to be harvested before the seeds become viable. Now there's something that can be not ok. Compost cucumbers and tomatillos can be the most healthy unplanned plantings you will produce.

If the heap is in contact with the soil, fruit/vegetable matter is great for attracting native earthworms which will then go on to consume all leaf matter and grind it into rich vermicompost.

So I fired up the TED talk and listened to it...

1. Sorry, composting doesn't start in fall with leaves or in spring when you start dealing with vegetable food waste. It's a year around process.

2. True, vegetable kitchen waste only will create a horrible mess, unless you're using the Japanese Bokashi fermentation method.

3. Sorry, wrong on the nitrogen content, fruiting plants move all their nutrients into the fruit and seeds in order to pass it on to the next generation.

4. Yes I agree, leaves are wasted by most people, and yes they have to be shredded if you want them to compost quickly. A lawnmower can do the shredding just as well as anything.

5. Worm bins? Never have needed them, that's what your compost heap becomes when you add kitchen waste.

What're Karma points worth, I do it for enlightened selfish reasons. I don't have to pay for hauling it away to be buried, and the garden food tastes so good! We probably agree wholeheartedly there.

Also, there are many composting methods. You don't even need a bin. And the easiest for kitchen waste is potholing. Dig a hole in between your intended plants, bury it and let the worms eat it. Plants will grow feeder roots into the remains.

Answer 2

I watched the entire video out of curiosity.

This is a classic case of someone with a little knowledge but some name recognition seeing a real problem and coming up with some incorrect conclusions. If the name of the talk was "A foolproof composting method for people who have trouble composting" I think it could have been useful to some. My guess is that that sort of speech wouldn't get him invited to present a TED Talk. Change things around a little bit to make it sound groundbreaking and controversial and boom you can scratch "TED Talk Presenter" off your bucket list.

Some of what he said in the video contradicts well established practices. Some are just plain dead wrong. Some of the analogies he makes contradict other things he said. He had written a book on composting and based on some of what I Read online it seems that the information in his book doesn't have the same thoughts on using vegetable scraps. I haven't (and wouldn't) read it myself.

The real problem, which he correctly identified, as people having a hard time making good compost by only using vegetable scraps, is a real problem for some.

Vegetable scraps, as you correctly identified (and the speaker erroneously contradicts) have about a 20:1 carbon to nitrogen ratio. That's fairly high and would need more carbon rich sources to get the recommended 30:1 ratio in your compost pile. The problem is that many people begin composting in the spring when the weather is nice and they're thinking about their garden. In the winter we're all holed up indoors under blankies sipping hot chocolate with marshmallows completely forgetting the fact that we even have a garden let alone a compost pile. :)

In the spring, we don't have the abundance of high carbon sources that we do in the fall. A lot of what people will have lots of are vegetable scraps, grass and other green yard clippings. This can be difficult to make good compost with.

That doesn't make vegetable scraps bad for composting, which it seems he mistakenly concluded. It means people aren't finding good sources of compostable materials that are high in carbon and also dry, because vegetable trimmings are high in moisture.

In the spring and summer some browns you can add to your compost to balance out the nitrogen rich stuff you'd normally add around that time include:

1. Any fall leaves that didn't finish composting over winter
2. cardboard boxes, newspaper, some junk mail and other paper products as long as the inks are safe and haven't been used with chemicals. For instance, don't compost that paper towel soaked in Windex after you've cleaned your windows.
3. wood chips or sawdust (if you're like me you're starting to do more home improvement projects in the spring) just don't use any painted or treated lumber.

Vegetable scraps are very good to ad to your compost bin as most reputable sources have indicated since forever.