Did you start a compost pile that just won’t heat up? If so, you are probably wondering why it happens, and what you can do about it.
So, why is your compost not heating up? Your compost will not heat up if it the moisture is wrong (it can be too wet or too dry). The size of a compost pile also matters: it won’t heat up if it is too big or too small. A compost pile will also not heat up properly if it is lacking nitrogen, air (oxygen), or bacteria.
An imbalance between “green” (nitrogen-rich) and “brown” (carbon-rich) materials can also prevent compost from heating up. As you can see, there are lots of things that can slow down the composting process. If you are diligent, you should be able to address these issues in no time.
In this article, we’ll look at the reasons why your compost is not heating up, along with things you can do to make it heat up faster.
Why Is Your Compost Not Heating Up?
When a compost pile is not heating up, it is often a case of extremes: either too much or too little of something. For example, compost will not get hot enough if it is:
- Too wet
- Too dry
- Too big
- Too small
- Lacking nitrogen
- Lacking oxygen
- Lacking bacteria
Any of these factors (or a combination of several) could prevent your compost from getting hot enough. Let’s go through them in order, starting with a pile that is too wet.
Your Compost Pile Is Too Wet
Normally, aerobic bacteria (those that need oxygen) work to decompose the organic material in a compost pile. Heat is released as these bacteria digest the contents of the compost pile.
When your compost is too wet, it does not get enough air (oxygen). When this happens, aerobic bacteria cannot survive to do their job.
This encourages anaerobic bacteria (those that do not need oxygen) to grow. When these anaerobic bacteria digest the material in a compost pile, they produce methane (a greenhouse gas), which has a foul odor.
So, if your compost smells foul instead of earthy, that is one indication that the pile is too wet. Another clue is that there is brown liquid leaking out of the compost bin or from the pile.
You can also feel your compost to tell if it is too wet. If you can easily squeeze water out of a handful your compost, then it is too wet.
How To Dry Compost
If your compost is too wet, there are a few ways to dry it out.
One way is to use a rake or pitchfork to spread out the compost thinly over a larger area. It will dry out faster if exposed to sunlight and air.
If the weather forecast calls for rain, use a plastic tarp to cover the pile and keep it from getting wetter. You might need to use a covered bin (a composter) if wet compost due to rain is a recurring problem.
Once the compost is dried out a bit, pile it back up and add some new material (greens such as grass and browns such as leaves) to help get it going again.
Another option is to add dry materials to the compost pile to help balance out some of the moisture. For example:
- Shredded paper
If you do decide to add sawdust, go easy and don’t add too much. Remember that sawdust has high carbon content.
Too much carbon can “bind up” the nitrogen in compost, making it unavailable to bacteria for decomposition. You can learn more about how to compost sawdust in my article here.
Straw is another good choice for drying out wet compost. Straw also has other uses as a growing medium – for example, growing potatoes.
If you use too many dry materials like straw and sawdust, you could end up with the opposite problem: dry compost.
Your Compost Pile Is Too Dry
Compost that is completely dry will also have trouble heating up. It will decompose slower, and it may not get hot enough to destroy pathogens (plant diseases) or seeds from weeds.
A compost pile made up of too much dry material (such as brown leaves, straw, sawdust, etc.) may not have enough water to decompose in hot, dry weather.
Having enough moisture in your compost pile encourages the growth of microorganisms (such as bacteria) that make the decomposition process possible.
Do You Add Water To Compost?
You can add water to compost with a hose or bucket, but don’t add too much. The pile should be a little moist, but not so wet that brown water leaks from the bottom of the pile.
You can also add materials with high water content (such as fruits and vegetables) to give your compost pile some extra moisture.
If you have lots of dry materials to compost, another option is to find some fresh grass clippings to add to the pile.
The key is to add enough material, but not too much. Remember that the size of your pile also plays a role in the composting process.
Your Compost Pile Is Too Big (Or Too Small!)
A compost pile that is too large may not heat up all the way through, leading to incomplete decomposition.
On the other hand, a compost pile that is too small may not have enough material for the bacteria to really get started. Such a pile may never heat up much at all.
For ideal composting, use a bit more material. According to the University of Illinois Extension:
“For most efficient composting, use a pile that is between 3 feet cubed and 5 feet cubed (27 to 125 cubic feet). This allows the center of the pile to heat up sufficiently to break down materials.”
Don’t worry if the compost pile seems too large when you start out. According to the Colorado State University Extension:
“Plants lose between 50 and 75 percent of their volume in composting.”https://extension.colostate.edu/topic-areas/yard-garden/composting-yard-waste-7-212/
That means your final finished compost pile will only be ¼ to ½ the size of the original pile.
Even with the right water levels and size, a compost pile can still suffer from a lack of nitrogen.
Your Compost Pile Is Lacking Nitrogen
When there is not enough nitrogen in your compost pile, decomposition will slow down, and the pile will cool off. Having too much carbon in your compost pile can also counter any nitrogen that is present.
“Microbial activity is greatest when the carbon-to-nitrogen ratio (C/N) is 30:1.”https://extension.uga.edu/publications/detail.html?number=C816&title=Composting%20and%20Mulching
Some materials that are high in nitrogen include:
- Coffee grounds
- Grass clippings
Materials that are low in nitrogen include:
Grass clippings are a good way to add “green” (nitrogen rich) material to your compost pile. They are also easy to find, making them a good cheap material to add to your compost.
If you are composting grass and leaves together, a good ratio is about 3 parts grass clippings to 1 part leaves. This will give you around a 30 to 1 ratio of carbon to nitrogen in your compost pile.
Manure is another option to add lots of nitrogen to a compost pile. A good ratio is about 3 parts chicken manure to 2 parts leaves.
This will give you around a 30 to 1 ratio of carbon to nitrogen.
Remember: don’t apply manure directly to your garden before it has had a chance to age! Pathogens can also survive if the manure is not properly composted before use.
“Research shows that 2 to 10 percent of bacterial pathogens survive the composting process. If manure is composted for food gardens, a two- to four-month curing process following composting is necessary to reduce pathogens. Favorable moisture and temperature conditions during curing allow microorganisms to develop and outcompete the pathogens.”https://extension.colostate.edu/topic-areas/yard-garden/composting-yard-waste-7-212/
In addition, both much nitrogen and excessive salts in animal waste can harm your plants. You can learn more about how too much manure hurts your plants in my article here.
One other option to boost nitrogen is to add fertilizer to your compost pile. You can learn more about high-nitrogen fertilizers in my article here.
Your Compost Pile is Lacking Air (Oxygen)
If your compost does not have enough air, then aerobic microbes cannot decompose the organic material in the pile. Anaerobic microbes can still do their work, but it is much slower, occurs at cooler temperatures, and might result in a foul smell.
According to the University of Georgia Extension:
“Oxygen is required for microbes to decompose organic wastes efficiently. Some decomposition occurs in the absence of oxygen (anaerobic conditions); however, the process is slow, and foul odors may develop.”https://extension.uga.edu/publications/detail.html?number=C816&title=Composting%20and%20Mulching
One way to add oxygen to your compost pile is to simply turn it over by mixing it up or moving it.
How Often Should I Turn My Compost Pile?
You should turn your compost pile 1 or 2 times per month (every 2 to 4 weeks). You can turn your compost with a pitchfork by moving the pile from one spot to another nearby spot.
If you have 2 or 3 separate bins, you can move the compost between bins to aerate it when needed. You can learn more about compost bins (and how big they should be) in my article here.
Your Compost Pile Is Lacking Bacteria
It may also be that your compost is lacking bacteria. After all, they are the creatures that heat up the pile as they do the work of decomposing organic material.
To solve this problem, you can add some ordinary soil from your garden to your compost pile. The soil contains bacteria that will be happy to go to work on the material in your compost.
How Long Does It Take For Compost To Heat Up?
In warmer weather during the summer, the time will be closer to 1 week. In cooler weather, the time will be closer to 1 month.
You can also speed up the process and make your pile hotter by addressing the factors mentioned above:
- moisture content
- size of pile
- air (oxygen)
Compost that gets hot enough will destroy pathogens and the seeds of any weeds in the pile. On the other hand, compost that does not get hot enough will decompose slowly, smell foul, and sometimes leaves behind dangerous pathogens.
How Do I Make My Compost Hotter?
There are a couple of ways to make your compost pile hotter, aside from those mentioned earlier.
First, chop up the material into smaller pieces. This will cause faster decomposition and higher temperatures will result.
“Grinding the organic material before composting greatly reduces decomposition time. The smaller the size of an organic refuse particle, the more quickly the microbes can consume it.”https://extension.uga.edu/publications/detail.html?number=C816&title=Composting%20and%20Mulching
For example, you can use a lawn mower to pick up leaves and chop them into leaf mulch before adding them to your compost pile.
Earthworms can also help by breaking down organic material into smaller pieces when they eat and digest it.
After all of your materials are chopped into small pieces, mix them together well. You want a good balance of nitrogen and carbon in all parts of the pile, rather than some areas where nitrogen is high and others where it is low.
Should A Compost Pile Be In The Sun Or Shade?
A compost pile in the sun will decompose faster because it will warm up due to the heat from sunlight. However, this assumes that the compost pile stays wet enough to keep the bacteria alive.
In hot, dry weather, sunlight might dry up your pile too much. This would be counterproductive to your composting efforts.
So, if you keep your compost pile in direct sunlight, keep an eye on it. If it dries out, add some moisture with water, vegetable scraps, or grass clippings.
Should I Use A Compost Starter Or Compost Booster?
You do not need a compost starter or compost booster. According to the University of Illinois Extension:
“Commercial starters are available but should not be necessary for compost piles that have a proper carbon to nitrogen ratio”https://web.extension.illinois.edu/compost/process.cfm
Compost pH: Does it Matter?
One more thing: let your compost age a bit before putting it right on your plants! According to the University of Missouri:
“The pH of the pile will be very acidic at first, at a level of 4.0 to 4.5. By the time the process is complete, the pH should rise to about 7.0 to 7.2.”https://extension2.missouri.edu/g6956
Some acid-loving plants, such as blueberries, would be delighted to live in a pH of 4.5. Other plants would not be so happy about acidic coil, so just keep that in mind when adding fresh compost to your garden.
Now you know why your compost is not heating up. You also know how to make compost heat up faster, and how to create the ideal conditions for making compost.
I hope you found this article helpful. If so, please share it with someone who can use the information.
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