Hot Composting: A Step by Step Guide

by | Aug 1, 2021

Welcome to the fourth installment in our compost series! We are going to talk about hot composting—how to do it, why it’s effective, and tips for maintaining a hot compost pile successfully.

Our hot composting experience

To give you a little background, we just started hot composting in the beginning of 2020. After having the desire to expand our homemade compost production, Sam and I created two large bins (outlined in our DIY Urban Pallet Compost Bin tutorial) and finished a full batch of compost in just about two months! Yep, two months for a little over 18 cubic feet of homemade compost in our urban backyard!

If you haven’t already, definitely read up on the basic foundation and principles of composting over at How to Compost: Filling & Maintaining a Compost Bin.

So let’s talk about some benefits of hot composting:

Hot composting can give you a nutrient rich soil amendment in as little as two months. 

The temperatures achieved can kill weed seeds and pathogens that could be in your compost materials.

It’s fun and let’s you truly watch the decomposition process at its best. 

And while there are benefits to hot composting, there are also cons. For example, it is more labor intensive. You will need to physically turn your entire compost pile every few days (temperature dependent). Another drawback to hot composting is the fact that you’ll need to have all your materials ready all at once for a big batch. The volume of your pile is truly what allows it to reach such high temperatures.

The largest benefit to hot composting, in my opinion, is the heat that can be achieved. Reaching temperatures over 145 degrees F gives me more confidence that pathogens and weed seeds are killed.

Our DIY wood pallet compost bin was new to the garden last year because we really wanted to challenge ourselves to generate more compost. This is how we learned how to hot compost.

My favorite tools for composting

1) Garden ForkI love this tool for turning a compost pile. In fact, I actually use a garden fork for a lot of tasks just in the yard. Forks are great for loosening up soil when pulling onions, garlic, or leeks.

Related article: How to Grow Leeks ~ An Easy Cool Season Crop

2) Thermometer– in a hot composting situation, we determine when to turn our compost pile by assessing the temperature. It’s pretty cool to see a compost pile heat up to 165 Degrees F! This is the thermometer we use.

3) Tarp– Sometimes a tarp comes in handy. Not only can you use it to cover a pile if you’d like, but we also use our tarp during the turning process. We shovel out all our compost onto a tarp, and then shovel it back into the bin. This helps ensure that all the material is mixed together well and can keep the ground more clean. A tarp can also be used to lay on the ground when sifting your compost.

A Quick Note on Urban Composting

We live in an urban area, so critters like rats, raccoons, possums, and more can be an issue. When we first started out designing our DIY compost bins, this was a major consideration. We also operate a “two bin system with a twist” that is outlined in the urban pallet compost bin article. Definitely read through that article for further details and tips!

Hot Composting: Step 1

Assemble all your organic materials.

The temperatures that are possible in hot composting are only possible because of the volume of the matter. A larger volume means more heat is generated and retained to help break down the organic matter and kill any weed seeds and pathogens that make it into your pile.

Layer all your materials into your compost bin. Remember to alternate between layers of browns (carbon) and greens (nitrogen). For full instructions on how to layer your compost bin and some examples of the browns and greens we use, see How to Compost: Filling & Maintaining a Compost Bin.

As you are layering your green and brown materials, remember to wet each layer with water. Over time you will learn how much moisture is too much, but your pile does need moisture in order to facilitate the break down of the pile. NOTE: the general rule is that your compost should be the texture of a wrung out sponge. This is true BUT in the beginning it is difficult to assess this characteristic because your organic materials are larger and not broken down at all.

Insert your thermometer into the center of the compost pile. We use a thermometer to make sure our compost pile is working properly and to know the best time to turn our piles. We use this thermometer.

Last but not least, cover your compost pile. Our DIY pallet compost bins have covers built in, but you can also use a tarp to cover your pile. This is especially important for those of us gardening in extremely hot and dry climates. Covering our compost bins will keep in valuable moisture by preventing evaporation into the atmosphere.

Here are the layers of our compost pile before we mix it in. It shows the 50-50 ratio of greens to browns that we use for hot composting.

Step 2: Your pile should get hot!

Within the first day or two, the pile should reach it’s max temperature for this cycle. For us, our temperature typically reads about 160-165 degrees F within two days when we get it just right. If you are using the same thermometer we are, you’ll notice that anything over 130 degrees F is in the “hot” spectrum. This is good. Not every pile will reach 160—we get really happy when ours does because that means we made a really good mix.

Step 3: Observe your temperature

Check the temperature of your pile every day. It should hold at the peak for 2-3 days and then start to fall. This is the natural cycle!

Always monitor moisture and make sure your pile isn’t drying out.

Check that your pile is not emitting a weird smell. If it smells like ammonia, you probably have too much nitrogen (greens). Try and fix these problems now so that you have the best ratio of browns/greens for maximum decomposition rates. Remember, I like a ratio of 1:1 browns to greens.

Here is our compost thermometer. We simply leave it in and check the temperature of our compost pile frequently.

*NOTE: sometimes I do need to gently tap on the thermometer with my finger to get an accurate reading, as our thermometer has become stuck a few times.

Step 4: The temperature falls

After a few days (sometimes more or less depending on your pile) the temperature will start a steady decline. You’ll notice our thermometer has sections that are divided into “hot” “active” “steady”. Once the temperature reaches “steady”( around 100°F) it is time to turn your pile. Turning your pile will re-invigorate the microbial activity and get the heat and decomposition going again.

When we turn our hot compost pile, we lay down a tarp and spill the contents out. I check for moisture and we “turn” the pile back into the bins.

Step 5: Turn your pile

My favorite tools for turning a compost pile are: a garden fork, a shovel, and a tarp. You can watch a video of how we turn our compost pile below. The tarp is how we keep the compost separate from our decomposed granite walkway. It also reduces waste as we can essentially get every crumb of compost we can!

As we turn the pile, the idea is to mix up the material to re-invigorate the microbes with air and introduce them to new material to break down.

During the process of turning our compost pile, I always check the moisture level. For a new pile, the chunks are still pretty large so I just eyeball the moisture level. As your pile breaks down more, you can do a squeeze test. Ideally, the texture of your pile should be like a wrung out sponge. To add additional moisture, I just water the layers as we add it back into the bin during turning.

Hot tip: to get that last, itty bit of compost off the tarp when you are done turning, we each grab a side and just flip the crumbs into the compost bin. I guess we make the turning of the compost pile a two person job. Haha.

It’s been very hot and dry, so I’m adding moisture to our compost pile while we turn it and as we layer it back inside the pallet bins.

Finishing your hot compost

Repeat the steps outlined above—observe, check the temperature, turn, etc.—-until the compost is finished! You’ll be mesmerized by how quickly your pile changes from simple scraps to gorgeous, earthy compost for the garden!

When a pile is finished, there are a few things you’ll notice:

LOOK. Finished compost will look like a rich amendment. It will be dark and crumbly, and none of the components should be recognizable (meaning you shouldn’t be able to identify any of the items you added).

FEEL. It should feel like moist soil and not have large pieces leftover. If you do see some large pieces, but the rest looks completely done, you can simply remove them and save them for the next load.

SMELL. Finished compost should smell earthy.

TEMPERATURE. If your pile is truly finished with the decomposing process, the temperature will no longer be in the “active range” nor will it reach the “active” range again.

This is our DIY backyard compost bin. We have two on our side yard.

How we use compost in the garden

I can honestly say that compost is my MUST have for the garden. It’s the one amendment I won’t do without! The way we use the majority of the compost we make is to amend each garden bed for a new season. After removing all expired, dead, or diseased plants I fill the beds back to the top with compost—this is usually a good few inches. For my full process on how I amend my beds, I cover it here: How to Amend Your Garden Beds Organically.

Side dressing with compost. Sometimes during the growing season, I’ll plop some compost around the base of my plants to rejuvenate and feed them. This is called “side dressing.”

Add compost into soil mixes for container growing. Anytime I’m potting up a plant, I’ll usually tickle some compost into the top layer.

Sifting your Compost

Sometimes there are thicker roots, branches, or coconut shells that don’t quite break down at the same rate. That’s ok, we just take those pieces and put them in the next round of compost. The best way I have found to get all those larger pieces out is to sift my finished compost. I don’t use a very fine sifter, like for baking. I tend to just use a nursery tray I have hanging around, but you could get a sieve that fits the top of a 5 gallon bucket like this one or use 1/2 hardware cloth to make your own. A 1/2″ mesh is large enough to not clog to easily, but still catch the large chunks.

I filmed the video below as I was sifting some compost to show you what I like to do sometimes.

~Hot Composting FAQs~

What is that white-ish grey residue on the inside of my compost pile?

As you are turning your compost pile you might notice that the inside might have what is almost fuzzy residue that is white or grey in color. This is called mycellium!

Mycellium comes from the latin root “myc” which is mushroom and is basically a fungal colony. This fungal network is beneficial and it’s appearance in your compost pile means that decomposition is occurring!

If you look closely, you can see the white-ish grey residue covering some of the contents on the inside of the pile. This is mycellium

Why is my pile breaking down more slowly?

Even though you are hot composting (which is typically faster than some other methods), there are many factors. 2-3 months for finished compost is fast and what happens when I really nail my balance of greens, browns, and moisture. It won’t always turn out like that. I’ve since made batches that take longer, but it does break down more quickly than if we had a passive, smaller compost pile. Lastly, remember that pile volume also matters. Smaller piles can’t always generate enough heat to reach or maintain hot temperatures.

What if I forget to turn my pile?

It’s gonna be okay! I’ve gotten busy and neglected my compost pile many times. When you don’t turn the pile, it just slows down the microbial activity and your pile will just start to slow down in the decomposition process. Often times, I just turn it again (check the moisture levels) and it gets back to hot (but not as hot) temperatures. Sam will even add grass clippings sometimes (to reinvigorate the pile) because they are a source of nitrogen that breaks down very fast and hot.

Do I need to chop all my greens & browns into small pieces?

This is all a balance. Smaller pieces will break down more quickly since more surface area is exposed BUT I personally feel that having varying sizes in a large compost pile can actually be most effective. Why? Leaving some larger pieces, or maintaining many pieces of different sizes, allows for better aeration of the pile which can help spur the decomposition process. If all your pieces are teen tiny, they can end up matting together and depriving that area of oxygen—-remember, air is an important element of the decomposition process.

In general, for tumbler composting or cold composting, smaller pieces do perform better. I have just observed that in our hot compost pile, the larger pieces really help the pile get very hot.

Ready to start composting?

Composting and gardening fit hand in hand. I hope this article has helped get you started on your composting journey. If you want to read more about how we use compost and other amendments to build healthy soil organically check out Amend Your Soil Organically ~ 5 Things To Do.

You can find many of the items that we used in our compost system on our Garden Supplies & DIY Amazon List, and please stay tuned for the next installment of our composting series: Hot Composting~ A Step by Step Guide

⇓ Have questions? Ask them below! Are you planning to start composting?⇓

Meet Randi

Urban gardening is my jam. I’m Randi, California girl who obsessively gardens to grow food and flowers around my urban home. Seasonal, simple living is what inspires me~ I hope it will inspire you too. Join me in crafting a life and home connected to the garden Read More>>>>

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