This is part of a larger STEM based lesson plan I put together that combines composting and sustainability lessons with computer science and web development. See more on github.
What is composting?
Composting is human controlled decomposition.
How is compost different from soil?
Compost is made of mostly organic materials. Organic materials are carbon rich materials that were living at one point in time or are made from something that was living at one point in time. Soil is mostly made of minerals and rock.
What are common organic materials?
- Food like fruits, veggies, grains, meat, and dairy.
- Clothing like cotton, wool, leather, and down.
- Paper products like newsprint, cardboard, and tissues
- Plants, animals, and other waste — grass clippings, leaves, bones, sawdust, ect.
How does compost ultimately help soil and plant life?
Adding organic material to soil provides food and nutrients to plants living there, increases the soil’s water retention capabilities, and allows airflow through the soil. All of these are important for sustaining life.
What is decomposition?
The last stage of the circle of life. When living objects die, decomposition is the process by which their nutrients are broken down and returned to the soil.
What are decomposers?
Decomposers are the living organisms that use the organic materials in the composting bin as food. This includes bacteria, fungi, and small insects. The “food web” expands out to larger things like worms, centipedes and other bugs as well. The compost pile is a big ecosystem full of life.
What are aerobic and anaerobic decomposition?
Anaerobic decomposition happen in the absence of oxygen, typically smells and is more acidic than you want when using compost in gardening. Aerobic decomposition uses oxygen and is the type of decomposition gardeners will want to encourage.
What are some normal types of composting (hot, cold, worm)?
Decomposition will happen naturally, and composting is just controlling that in some way, shape or form. You can have just a fenced piles of leaves and waste, a bin of worms at home, or you can do a hot composting operation with outdoor bins you actively turn. It all just depends on your space and time. The questions following deal with hot composting methods.
I don’t have enough space for large volume, can I not compost?
Yes, you can. Your pile will take longer to break down and it won’t get as hot. You can use the rest of the information found here, but your mileage may vary in regards to timing and temperatures.
Recipe and care
What are the ingredients to ideal controlled decomposition (aka composting)?
Pretty much what all humans and animals need. You need to provide a good environment for sustaining life of decomposers.
- Food— Carbon and Nitrogen rich materials
What are Carbon and Nitrogen rich materials?
See the organic materials list above. Carbon rich materials are objects like dried leaves, newspapers, wood chips, ect. Nitrogen rich materials are items like food scraps and coffee grounds. You want and need both to create a pile that decomposes quickly and doesn’t smell like rotting food.
How should I mix them all together?
Make sure things are chopped up and shredded well. This provides more surface area for the decomposers to do their work. (Think how crushed ice melts faster than cubed ice, same principle).
When do I turn?
Weekly should be sufficient. Just make sure air gets in there.
What are the stages of decomposition and what do I do during them?
There are about four stages. If you can, try to not add a bunch of materials once you have a big mix going. Or at least set aside one bin for collection while the others just get to bake and break down.
- Heating up. After a good mixing, the first week the pile heats up quickly. If it isn’t, you’ll want to check you had a good mix and the pile has enough volume to self-insulate.
- Hot. The next few weeks you should reach your peak temperature. Just let things bake and turn it weekly.
- Cooling down. At this point, even if you turn things, you won’t be able to maintain heat. The pile should smell earthy and not have any identifiable items in it. Move it over to a finishing pile.
- Finishing pile. Leave it be. Just let things sit for another few weeks before you sift it and add to your garden.
Rules of Thumb
What can I compost?
A better question is what can’t I compost. Everything decomposes, but if you’re doing a home or garden operation — avoid meats, oils, cooked food, plants that have been sprayed with pesticides, non-shredded wood/mulch, and weeds that have seeded.
What type of bin should I get?
Depends on your time and space. If you have time and a good plot of land, lookup plans for a three bin compost system and make sure you turn it once a week. If you do not have that space and time, then get a couple bundlers or trash bin style bins and give them a little aeration every week.
How do I know it is working/doing what it is supposed to do?
The pile will heat up and stay heated, the size will reduce significantly over the course of the weeks (around 50%), and after 4-6 weeks, everything will have a dark, crumbly texture and an earthy smell.
When is it done?
After 4-6 weeks, there should be no identifiable objects left in the pile. It should have a cool, dark brown, crumbly texture and smell earthy. One test you can do is place some in a plastic bag overnight, if you open it up the next day and it smells terrible, it’s not quite done yet.
How do I know if something is going wrong?
Use your hands, eyes and nose. If the pile is not heating up, you need to work on your mix of carbon and nitrogen materials. Double check that there’s moisture. In general, smaller piles heat up less. A pile that is 27 cubic feet can reach temperatures north of 120 degrees if mixed well. If it smells bad, you either need to reduce moisture or add some carbon heavy materials.
How do I use it when it is done?
Mix it in well. Don’t just layer a little on top. Really mix it in or add several inches to the top.
Community Garden Operations
What’s a good setup to have at a community scale?
Your milage may very, but this setup typically works well.
- Three bin system. One for collection. Two for cooking.
- Finishing pile section. An area or bin just for finishing compost.
- Sifter. Some sort of sifter to sift the good compost material from the larger chunks and twigs that will inevitably be mixed in there.
How do I collect and what should I accept?
Be consistent. Have a regular drop off time during the weekend and have a regular bin that people drop off their materials. Be on the safe side of what you accept. Food scraps are great for Nitrogen, just avoid meat as it attracts rodents. Leaves in the fall and sawdust are good for browns.
How do I manage the bins?
Again, just be consistent. Have a regular time where you or other members turn the bins and check in on any maitence. Once a week for two hours should do the trick.