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Hot Composting

Updated: May 9, 2023

Composting is a popular way to turn yard and kitchen waste into a usable soil amendment for your garden. Hot composting is a much faster composting method that focuses on the microbial activity to decompose the material. The key to hot compost is the right mix of browns and greens, air and moisture. Brown to green ratio should be 25-30:1. This ratio has always seemed hard to put into practice. What does 30:1 really look like? To make things easier just add 1/3 green to 2/3 brown. If you add a bucket of green, add 2 buckets of brown.

Let's talk browns and greens. Browns are your carbon source such as dry, SHREDDED (more on this later) leaves and wood chips, and greens are your nitrogen source and they include coffee grounds, untreated grass clippings (I don't use these, and I will explain in the next paragraph), green leafy material like from your garden (a few caveats here) and kitchen waste (no meat, dairy or cooked food).

Shredded leaves and/or wood chips are the key for your hot compost pile. Leaves that are not shredded will not break down as quickly and will become matted and reduce airflow. I made the mistake of starting a pile with leaves that were not shredded and it was not ideal, and I have since switched to shredded only.

Grass clippings: many people use grass clippings as their green compost material. I do not because our yard is treated with chemicals. If you introduce herbicides into your compost then they can affect what you grow in the finished compost. Additionally, grass clippings are ten percent nitrogen and are great for your lawn. We do not bag our grass clippings and leave them on our lawn to fertilize the grass. If you have access to chemical free grass clippings, they are a good Nitrogen/green addition to your pile.

Garden waste- I use plants I pull from my garden as they die or as the season changes ONLY if they are completely free from disease and pests. The last thing I want to do is deal with diseased plants or extra pests when I use the compost. Technically, hot composting should kill disease pathogens, seeds and weeds, however, I don't want to take the chance.

Kitchen waste- Do not use any meat, dairy, bones, anything with oil or cooked food in your compost. Fruit and vegetable scraps, work but if large can take a long time to break down. If you are composting in an open bin then you also have to worry about animals getting into the bin. If you have an open bin, kitchen scraps are not necessary if you are worried about animals. Surprisingly, food waste provides negligible nutrition to the finished compost. When I add kitchen scraps to my compost piles, I make sure to dig a hole and bury the scraps. I use a worm bin (vermicomposting) to break down my kitchen scraps also.

When I first composted many years ago, I did it all wrong. I bought a plastic square compost bin with a "coal chute" opening at the bottom. You load the composting material from the top and get compost out the bottom once it has had time to break down. Sounded great until it wasn't. The problem with this rectangular plastic bin was the inability to easily turn the material. I ended up just adding material and never turning it. Technically, you don't have to turn a compost pile. You can let it sit and over time it will eventually break down (think 6-12 months), but I wanted compost in a shorter time frame.

I added mostly kitchen scraps to the bin and very little "brown" material. This is probably the most common mistake made when composting. If your ratio of brown to green material is off with way more green, you get a gross, stinky, fly infested mess.

My second attempt at composting is on the heels of lots of research to figure out how to get it right. I used 3 wood pallets to create an open bin. The recommended size of a hot compost pile is around 4 feet wide and 4 feet high. Mine is closer to 3 feet wide and probably at 2 feet high in the picture below.

I purchased a leaf shredder and started vacuuming up the fall leaves and mulching them like crazy. I added several bags of shredded leaves to the bin, followed by several bags of used coffee grounds from a coffee store. I saved all our coffee grounds and eggshells from the house and added those as well. I didn't layer my browns and greens but mixed them well with a pitchfork. After mixing all the ingredients I used the hose to wet everything to a wrung out sponge level.

I purchased a compost thermometer from Amazon and I was set. Within days my pile started heating up and after about a week (I was constantly adding more shredded leaves and coffee grounds and watering and turning the pile), the temperature moved into the active range.

I plan to continue to add to this pile until it reaches the top and then I will stop adding and keep the moisture level right and turn it every 4 days or so. The goal is to reach 131-149F (55-65C)

The goal is to have usable compost in time for my spring plantings which for my zone 7b/8a is about 5 months away. Finished compost will be dark brown, warm and smell good, and another way to know it's ready is that earthworms will appear as it has cooled down enough for them.

In summary, SHREDDED leaves, wood chips, coffee grounds, egg shells, non diseased garden green leafy waste, and kitchen scraps are what I am using in my hot compost. I keep it wet but not too wet (able to squeeze one or two drops out of it) and turn the pile every few days.

UPDATE: I have received a truckload of wood chips since writing this post. The addition of wood chips to my compost piles has helped heat things up tremendously. I used the app Chip Drop and it was a wonderful experience. Chip Drop matches you with tree companies working in your area. The tree company pays a fee to use Chip Drop, but it's free to the person requesting chips. I put all my information in the app and within 3 hours I had a tree company call me to confirm that I wanted chips and where on my property I would like them dumped. By that afternoon I had an entire truckload of wood chips in my driveway. You have the option of paying $20 to help offset the costs for the tree company, and I've heard that can help move your name up the list to get chips. Additionally, I checked the box for allowing some logs to be in my chip drop which can also help get chips faster. (Mine ended up not having any logs) There were still some small branches in my chips but since I am using my chips for compost as opposed to mulching pathways, it was not a problem. If you would like wood chips for your compost piles I can recommend using Chip Drop for free wood chips.


"You Bet Your Garden" podcast by Mike McGrath

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