DIY Soil Fertility – Part 4: Thermophilic Compost

Welcome to DIY Soil Fertility For Homesteads!

This post series covers the many ways you can build fertility, create soil, cycle nutrients and take responsibility for “waste” streams on your property – all with materials and substrates you are likely buying already or can be sourced for free or very low cast. These systems all integrate with one another to enable you to in-source your soil fertility inputs instead of relying upon centralized commodity supply chains. By employing these systems together in an integrated system you will improve nutrition (for soil and humans) and save dollars, while making living soil fertility enhancers better than anything you can buy at the store. The posts are written from our own experience and are geared towards the DIYer, though options are provided for ready-to-go purchased systems as well. Check the link tree below or at the bottom of the post to explore the rest of the series!

What Is Thermophilic Composting?

Thermophilic composting processes are set up to favor thermophilic (“heat loving”) microbes that are capable of rapidly breaking down organic matter into humus. Thermophilic composting is a way to make large quantities of quality compost in a relatively short period of time, and is typically done in meter square piles (the smallest a functional thermophilic can be) or windrows (if more material is available).

Thermophilic composting requires a lot of material and space compared to many other composting methods. If you have an abundance of high-carbon materials and nitrogen-rich inputs you can make a thermophilic pile that will get hot enough to cook and kill any weed seeds and pathogenic organisms in the material.

Compost that you buy at landscaping yards, home improvement stores and garden centers, whether by the yard or in bags, is compost that has gone through a thermophilic process.

How To Make A Thermophilic Compost Pile

Assemble Your Materials

Thermophilic compost piles are best assembled all in one go. It is helpful to gather and stage your materials so that everything you need to create a pile that will get hot quickly is at your disposal. You will need high-carbon materials (the “browns”) and nitrogen-rich materials (the “greens”). The ideal ratio of carbon to nitrogen in your pile is anywhere from 25:1 to 30:1.

The “Browns” – Carbon-Rich Materials (anything with a C:N ratio of 30 – 50:1 or higher – these will take longer to break down to higher the C:N ratio)

• Straw (75:1)
• Corn Stubble (60-75:1)
• Sawdust (500:1)
• Dry wood chips, finely shredded (400-700:1)
• Dried leaves (60-150:1)
• Dry Pine Needles (80:1)
• Shredded cardboard (350:1)
• Shredded newspaper (175-250:1)
• Nut or grain (35:1)
  • Peanut (25:1)
• And many more…if it is brown and dry its probably a good carbon source.

The “Greens” – Nitrogen-Rich Materials (anything with a C:N ratio less than 25-30:1 – these will break down fast)

• Livestock manures
  • Rabbit (8:1)
  • Horse (18:1)
  • Chicken (12:1)
    • Aged Chicken Manure (7:1)
  • Cow (16:1)
• Fish (7:1)
• Urine (1:1)
• Fresh Lawn clippings, still green (25:1)
• Hay (25:1)
• Wood Ash (25:1)
• Spent brew mash
• Fruit pulp (25-40:1)
• Fresh cut herbaceous greenery (20:1)
• Kitchen food scraps (25:1)
• Seaweed (19:1)
• And many more…if it still has moisture in it from when it was alive or being digested, it’ll typically contain decent amounts of nitrogen.

Making Your Pile

1. Begin by clearing a level area for your pile. Having a level floor will help your pile remain a pile instead of slumping as it is broken down by the thermophilic microbes.
2. Prepare your materials. If you have access to dry carbonaceous materials, manure and fresh cut green material in decent quantities you’ll everything you need to make a good thermophilic compost pile. Generally, a 1:1:1 ratio of each material type with enough volume of each to make a 4′ x 4′ x 4′ pile, when prepared well and combined, will create a pile that is both large enough in size and properly balanced between carbon and nitrogen to get up to thermophilic temperatures (140-145 degrees is a good range to shoot for).
   • Shred your carbon sources into the smallest practical sizes – large pieces of carbon rich material will break down too slowly and create a non-uniform finished product, which will require more sifting if you want to use it in an annual veggie garden etc.
   • Chop animal manures into small pieces, and rehydrate if they have dried ( for example, dried horse manure will not decompose uniformly because the middle of each clump will remain dry if not pre-hydrated when creating the pile).
   • Shred or cut finely any fresh cut greens – again, the smaller the pieces the more uniform their distribution and thus the better your pile will perform.
3. Start with a 3-4″ thick layer of carbonaceous materials for the bottom of the pile.
4. Follow with a thinner layer of nitrogen-rich materials (i.e. grass clippings or kitchen scraps). More dense nitrogenous materials should be applied in thinner layers (grass clippings) whereas less dense nitrogenous materials can be added in slightly thicker layer (fresh cut herbaceous greenery, tomato vines etc). Creating these layers such that the pile gets up to temperature quickly will take experience that can only come from doing. If you have dried carbon, manures and fresh greens, add them in a 1:1:1 ratio mixing them as thoroughly as possible to create a uniform distribution throughout the pile as it grows.
5. If materials are dry wet them as you go – don’t soak, but also don’t skimp. Ensuring that all materials are evenly moist is critical to getting the pile up to temperature quickly. The pile will likely take a lot more water than you might think unless you are utilizing inputs that are already hydrated (i.e. leaf mold, brewery wastes, fresh manures etc). If you have a few people assembling the pile, one person can continuously be spraying the pile while the other add material.
6. Activate your pile. Activators are things that will help kick the pile off and get it up to temperature quickly. Add your activators when the pile is halfway built, right in the center. Various Types of Compost Activators
   • Plants: comfrey, nettle, yarrow – chopped up fine
   • Small Animal Bodies
   • Fish
   • Finished compost
   • Biologically active soil
   • Urine
7. Continue layering materials in this manner, wetting as needed, until you have a pile that is at least 4′ in diameter and just as tall (taller and wider is just fine too). If you are blessed with more materials that will fit in this footprint, simply extend your pile, keeping the 4′ width and height for as long as you have material – you’ve now made a thermophilic compost windrow!
8. Finish your pile by covering it loosely with a tarp – you still want to allow air to circulate while also keeping humidity high around the pile. If you are worried about your pile not breathing properly with the tarp, place a wire cage atop your pile and then place your tarp on top of the cage to create an air pockets between the tarp and outer layers of your pile.
9. Your pile can now sit for ~ 4 days.

Monitor And Turn Your Pile

Your compost heap, if well made, properly hydrated, and kept insulated from moisture loss and temperature swings, will increase in temperature over the following 4 days. We recommend using a compost thermometer (buy once, cry once) so you can known what is going on in the center of your pile – this will help you determine how well your recipe is working and when it is time to turn your pile.

Depending on the carbon to nitrogen balance in your pile, the uniformity (or lack thereof) of moisture, and the amount of aeration, you may see temperatures ranging from 100 to 180 degrees. Either ends of this extreme are signs that your pile is out of balance. Ideal internal temperatures to shoot for are generally in the range of 140-145 degrees Fahrenheit, but anywhere between 130 – 150 will do the trick.

Too cold usually means the pile is either too heavy with carbonaceous materials or too dry. Too hot usually means the pile was too rich in nitrogen – these piles will also tend to smell a bit, a ready indicator of excess nitrogen and/or anaerobic conditions.

Troubleshooting

Not getting hot enough? To remedy a cold pile, check for adequate moisture levels throughout the materials (dry sections won’t have any breakdown occurring, and will thus be colder, and overly wet sections will have anaerobic decomposition occurring, and also be colder). Large chunks of high-carbon materials can cool a pile, and should be shredded upon turning before reincorporating. You may potentially need to add more finely cut nitrogen rich material if there isn’t enough “fuel” to get the bacteria count ramped up. You may also simply need more material (if it isn’t large enough it won’t get up to temp).

To remedy a pile that is too hot, turn it and aerate it well. You may potentially needs to add more carbonaceous materials, particularly irregularly shaped materials (prunings, large dried leaves, sticks and twigs) to help create a more breathable structure within the pile to prevent anaerobic pockets from forming. If a pile is in the 140-150 degree range but is not cooling down (this can go on for months in some cases) it is indicative of anaerobic conditions, and the pile should be considered as putrifying organic matter (POM) and not be used to make compost given the likely presence of large amounts of anaerobes and potential pathogens.

To remedy a pile that smells bad or is too wet (a sign that nitrogen and/or moisture content is too high and going anaerobic, and therefore favoring the kinds of microbes you don’t want in your garden), set up an old wooden pallet or make a nest of branches and twigs on the ground next to the pile at least 6″ high. Then turn your pile onto the pallet or nest of sticks – this will allow air to get in from the bottom of the pile, and improve drainage. Consider adding more finely shredded carbon when turning as well. Then take the handle of your pitchfork and drive it down until you reach the bottom of the pile then stir it around to make a chimney in the center of the pile. The heat from the decomposition process will create a chimney effect, drawing in air through the bottom and exhaling it out the top of the pile, helping to gently dry it. If you are trying to dry a pile during wet weather, create a wire cage and place than on top of the pile, then pull your tarp over that to allow room for the chimney to function and to limit anaerobic pockets from developing between the tarp and the pile’s surface layers.

The general idea is after 4 days of letting your pile sit, you then begin to turn it every other day for the next two weeks (this is the best case scenario, with a good recipe, well-prepared ingredients and a nice hot pile). You may have to move slower or faster than this pace. When your observations tell you its time to turn your pile (either the pile has begun to cool, or isn’t getting hot enough, or its too hot, or it smells off – a proper pile should not offend the nose), begin by “peeling” the outer layers off of your pile and forming a new pile next to the old one. These layers that were previously not being broken down by the thermophilic bacteria will now be moved to the core of the newly formed pile, getting their turn in the sauna! Continue peeling and piling until you have essentially turned the pile inside out. Made adjustments as you go – moisten dry spots, break up large chunks of single-type materials, and aerate.

Finishing Your Compost

Finished compost can be made using this process as quickly as 18-21 days. A well-made pile can be turned every 2-4 days depending on where it is in the thermophilic cycle. As your pile nears maturity, the temperatures will slowly being to decline – though it will still be warm. There are many ways you can go at this point. By allowing your pile to sit for a while, perhaps covered with a tarp to keep it humid inside, or insulated with a fresh layer of leaves, the balance of organisms will begin to shift. Fungi will begin to establish themselves (now that you’ve stopped turning the pile and things have cooled down a bit) and a wide range of additional macro-fauna will take up residence – mite, springtails, spiders, ants, various beetles, worms, slugs, snails, centipedes, millipedes – in addition to the already present bacteria, protozoa and nematodes.

Using Your Compost

Depending on the original inputs of your pile and how thoroughly cooked they got, you may need to sift your compost in order to ready it for use in your garden. If applying to broad acreage or tree crops, no sifting is required – coarse compost will do just fine. However, your typical vegetable garden might appreciate a finer finished compost material, in which case sifting is called for.

Depending on the scale at which you are making compost different sifter designs may be more or less appropriate. We made a sifter that fit over our wheelbarrows, which allowed finished compost to be forked into the sifter, and then the sifted material would fall right into the wheelbarrow bucket, and we could easily discard the coarse material where it could be incorporated into the next compost pile.

Our design was very similar to the one showcased in the video below. For the typical home gardener, this set up should be more than adequate (we used this one to sift all the compost for our 1/3rd acre market garden).

A finished batch of healthy, thermophilic compost also makes an excellent inoculant for brewing compost tea. If you’re using a similar DIY homestead scale bucket brewing system as we do for our home gardens, just add a handful of finished compost to your tea brewing bag, along with worm castings from your vermicompost system, and you’ll help to increase the diversity of microorganisms present in your tea.

Resources For Continued Learning

Making compost is a beautiful mix of are and science. There is a quickly growing body of knowledge – both experimental and anecdotal – to learn from on the road to becoming a Compost Master Chef!

• Elaine Ingham’s Soil Food Web – check out her courses and publications if you really want to get nitty-gritty!
• Our YouTube playlist with some of our favorite thermophilic composting videos – some of which are featured above.
• Chelsea Green has a number of books on composting or with sections on thermophilic and other methods of composting.

Explore The Entire Soil Fertility Series