Compost is a valuable addition to any garden, but an unbalanced and untended compost pile is like a stew left simmering on low heat. It takes a long time to finish, and even with patience, the texture will still be pretty chunky.
While you can make compost slowly — throwing yard waste and kitchen waste in a pile and walking away — it may take a year or more to fully decompose. Worse yet, compost that stays too cool will preserve living weed seeds, insect eggs, diseases, and other pests you don’t want to add to your garden.
If you’re running short of time, and can’t wait more than a few months for good quality compost, you’ll want to speed up composting. The key is turning up the temperature.
Fortunately, raising the temperature of compost is easy, in any growing zone, if you know the recipe.
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How to speed up the composting process
You can start a hot compost pile any time of year because weather conditions do not directly build-up heat. Heat generated from the compost pile is a result of a thriving bacterial population, which you may influence by using the right ingredients.
To make hot compost you need five key ingredients:
- Carbon-rich “brown materials”
- Nitrogen-rich “green materials”
Although balancing these ingredients is the key to a hot compost pile, you don’t need to worry about precise measurement. Vegetation wants to decompose, and microorganisms want to help, so you just have to create the conditions to let nature take its course.
Following this recipe will help you raise the temperature of your pile, ideally to 140 degrees Fahrenheit, killing off pests and speeding up your time to completion by months.
Add Brown Materials
Brown material will make up the majority of your compost pile. Brown material is high in carbon and low in nitrogen, so it serves as the primary energy source for the microorganisms that convert your yard waste into compost.
Autumn, when dead leaves are abundant, is a great time to create compost piles. Dead leaves have a high ratio of carbon to nitrogen, making them a perfect bulk material for your pile.
However, many other scrap materials from your home and garden are similarly high in carbon, so you don’t have to wait until the leaves drop. Brown materials include other dry yard waste products that are high in carbon, such as hay or straw, weeds that have been pulled and left to dry in the sun, and wood debris like fallen branches, twigs, or sawdust.
Even cardboard, plain white or brown paper (nothing colorful or shiny), human hair, dryer lint, and natural fiber fabric (such as denim, cotton, silk, and wool) can be shredded and used as brown materials.
To speed up decomposition, chop them into smaller pieces. The smaller the brown material is, the easier for it to decompose. To process your brown material for quick composting, use a leaf shredder or a chipper.
Adding Green Materials
When a compost pile won’t heat up, one of the most likely causes is skimping on green materials. A pile made up of mostly brown materials will eventually decompose, but it may take a year or more, produce unpleasant odors, become acidic, and include undecomposed chunks of materials.
Adding nitrogen is critical to balancing, warming up, and hurrying up your compost because nitrogen provides microorganisms the proteins they need to grow and reproduce. The more microorganisms, the faster you will achieve finished compost.
Fortunately, there are a wide variety of free and widely available sources of nitrogen-rich plant materials you can add to heat up your compost.
- grass clippings
- fruit and vegetable waste
- coffee grounds.
You can even add a handful of organic nitrogen-heavy fertilizer to kick-start the process, but it isn’t necessary for decomposition in a healthy compost pile.
Manure is another great source of nitrogen. In fact, while manure is a great fertilizer, it is so high in nitrogen that it can burn your plants if you add it to the garden without composting it first. Using manure to heat up and speed up your compost pile is a win-win.
Balancing brown and green materials
Calculating how much of each ingredient to add may seem daunting — given that green materials include some carbon, and brown materials include some nitrogen — but the good news is there’s no need to worry about precisely measuring the materials you add to your pile, estimating is fine.
Most experts, such as the University of Missouri’s Extension Office, recommend a 2:1 ratio of brown material to green material. However, other extension offices recommend a 4:1 ratio or even a 1:1 ratio.
Given this variation, feel free to use trial and error to find the best blend for you.
Start with a mix that is roughly 2:1, using what you have on hand, and trouble-shoot if problems arise. If you find your pile is not heating up, try adding more green material.
If your pile smells like ammonia, that means it is releasing nitrogen into the air, so try mixing in more brown material.
When the interior of your pile feels warm to the touch, or you can see steam rise when you stir the pile in cool weather, you’re on the right track. If you want to track the precise temperature you can use a compost thermometer.
Encouraging beneficial microorganisms
While composting may appear to work like magic, your compost pile’s decomposition is actually the result of the hard work and hearty appetites of the bacteria, fungi, molds, yeasts, insects, and worms living in your compost pile.
Microorganisms decompose your compost by consuming it, giving off heat in the process, and creating nitrogen, phosphorus, and magnesium-rich compost that is worth its weight in gold in the garden. Creating a healthy environment for these microorganisms, as well as worms and insects, is key to hurrying up the processing of your compost.
Fortunately, encouraging microorganisms in your compost is easy. You can add redworms or earthworms if you’d like, but long as your compost pile is in contact with the earth (i.e., not in a container with a bottom), plenty of microorganisms, worms, and other beneficial insects will be naturally attracted by the buffet you’re offering.
If you create a pile with a good ratio of green and brown materials, and you ensure that their water and oxygen needs are met, these critters will happily help eat up, speed up, and heat up your compost pile.
However, if you are concerned about the presence of microorganisms in a newly created compost pile, an easy solution is to add a layer of garden soil from your yard (not soil from the store) to your compost pile. Along with the soil, you will be adding plenty of naturally occurring microorganisms. You could also try an organic compost accelerator to add microbes directly to your pile, although this is typically more helpful when used in contained compost bins, in which the compost is not in contact with the earth.
Proper hydration is essential for hot compost. A dry or soggy compost pile will not host a thriving community of microorganisms, and therefore will not heat up.
Your pile should be damp to the touch, but not so wet that you can squeeze much water from a handful taken from a recently watered pile. It should have a texture something like a wrung-out sponge.
If your pile is too wet, consider moving it to a more protected location or hanging a tarp over it to shield it from some of the direct rainfall. Other options include adding more dry brown materials, or when you turn the pile try spreading it out temporarily over a wider area so it will dry out a bit.
If your pile is dry, irrigate it regularly. You could also partially enclose the pile to create humidity (by using a container designed for compost, or by digging a pit and building your pile inside it) or simply move your pile to a shadier spot to reduce evaporation. However, to maximize heat it is preferable to give your pile full sunlight and water it as needed.
One of the most common errors in composing is to “set it and forget it.” In fact, “turning” your compost (i.e., stirring it up) is the key to keeping it properly aerated. Aeration, in turn, is key to heating up and speeding up the composting process.
While an unattended pile will eventually decompose, an anaerobic (oxygen deprived) compost pile can accumulate acid, lowering the PH level, which is harmful to essential microorganisms. Anerobic compost is slow, cold, and often smells like a sewer. Fortunately, turning your pile will solve all of these problems.
Compost heats up near the core, so once your pile is hot turning it will redistribute the heat throughout the pile to make the decomposition more consistent. Moreover, if the pile has cooled down because the material in the center has already decomposed, turning it will allow new undecomposed materials to form a new center and reheat the pile.
Typically you should turn your compost no sooner than after the first two weeks, and no more often every two weeks thereafter, to ensure it has time to get hot, and turning every 4-5 weeks may be adequate for your pile.
The easiest way to turn your compost pile is to prepare an empty spot (ideally right next to your existing pile) and use a pitchfork to move the compost materials from the current pile to the new location.
You may find that a manure fork — with its widely spaced thinner tines — works best early in the composing process, when the chunks are bigger. In contrast, later in the decomposition process, when your compost is fine and crumbly, it will be easier to move using a snow shovel.
A hot compost pile should be at least a cubic yard, to ensure it is large enough to create a buffer around the hot core. However, make your pile substantially larger and it may become difficult to turn regularly. A pile three feet tall and five feet wide and deep is a good starting place.
Because of the need for a large pile, commercially available compost containers are often too small to create a naturally hot pile. However, a large compost container made of black plastic may absorb enough heat via sunlight to make up for the slightly smaller size. If your compost is in a container, you will need to dump it out and refill it in order to turn your compost.
Time to get cooking
To get fully decomposed, weed- and disease-free, garden-ready compost as quickly as possible, all you need to do is turn up the temperature.
By starting with a proper balance of brown and green materials, and encouraging volunteer microorganisms by keeping your pile damp and aerated, you will see a wide variety of benefits. This recipe will raise your compost’s core temperature to roughly 140 degrees, prevent unpleasant odors, and accelerate decomposition, helping you achieve rich, dark, perfectly textured compost in just a few months.
If it’s your first time to make a compost, you can learn more on how to compost yard waste. If you have any questions, or you know any other tricks for heating up a compost pile, please share them below!