What’s the Difference Between Hot, Cold, and Warm Composting?

by Matt Gibson

Do you know the difference between hot, cold, and warm composting? Well, you are about to know a whole lot more about all three methods, and how you can use each to improve your garden’s soil, making it easier to grow healthy, happy plants each growing season.

Composting is the practice of recycling decomposing matter (such as your kitchen food scraps) and turning it into gardening soil that is rich in organic content, or a terrific soil amendment for your garden, to replace the nutrients that it loses during each growing season. What happens in your compost pile is a direct result of several factors: what you put into it, which method you choose to use (hot, cold, or warm), the size of the pile itself, the weather in your area, and how often you stir and maintenance the pile. All of these things can affect how quickly you can turn your trash into garden gold.

Another important factor to consider is that smaller pieces, such as chopped food trash, shredded leaves, and chipped wood, all tend to break down much faster than bigger pieces of wood, full leaves and food trash that is simply thrown in without being broken down a bit before hand. Just about everything that is made up of organic matter can be turned into compost. You might be surprised at all the things that you can add to your compost pile.

Hot composting is the quick method of turning your scraps into nutrient-rich soil, but it also requires more attention and maintenance than cold composting. The cold composting method requires very little effort to create and maintain, but a lot of time must pass before the mixture will break down enough to become useful in your garden beds.

Both methods have their positives and negatives, but composting problems are pretty easy to fix. Some gardeners swear by hot composting while others stick to the easier (but longer) cold composting method. Many gardening enthusiasts have both a hot and a cold composting pile. The warm (or hybrid) compost pile lies somewhere in between the two methods, and has become more common in recent years. 

No matter what method you choose, however, the end result is worth the time and effort, as you are creating a powerfully potent dose of nutrients that your plants will thrive on. Mix the end result into your garden’s soil, and give your garden the nutrient boost needed to produce healthy new plants in the coming season. Read further to find out which method is right for you and get started now. The quicker you start recycling your food trash, the sooner you will be able to improve your garden’s soil, which naturally loses nutrients over time.

Hot Composting

The quickest way to make a healthy batch of rich garden humus is by creating a hot or active compost pile. Hot compost piles can reach temperatures as high as 160°F, though the ideal temperature range is about 110°F to 140°F. At that level of heat, disease-causing organisms and weed seeds can’t survive. The size of the pile, the ingredients used, and the layered arrangement of the ingredients, will all have an effect on the success or failure of your hot composting setup. 

Hot Composting – Size

The perfect size for a hot composting pile is a four-foot cube, but a three-foot cube will do the trick as well, especially for smaller garden spaces. As you prepare your hot composting pile, adding in lots of decomposing organic matter, the pile will grow in size. As the compost starts to break down in the heat, the pile will begin to shrink, creating a garden rich humus that will keep your garden thriving year after year.

Hot Composting – Ingredients

• Two thirds of the ingredients which should be added to your soil base should consist of high-carbon materials such as dry, shredded leaves, small pieces of wood (like twigs and stems) and corn cobs.
• One third of the soil mixture should be a high-nitrogen dose of green plant matter. To make this mix yourself, simply combine small pieces of grass, weeds, plants, vegetables, trimmings, and kitchen scraps (aside from fat, meat, and dairy products). 
• Standard high-quality potting soil (The base substance to which the high-carbon and high-nitrogen ingredients are added) is the only other ingredient needed to start your hot composting system.

Hot Composting – Preparation

Create a layer cake of ingredients inside of your compost cube (or box). Start with a layer of high-carbon materials to line the bottom of the container. The best high-carbon materials to use for the bottom layer are twigs and woody stems, which will help to aerate the pile. On top of the carbon-rich layer, add a layer of soil. The third layer should be a high-nitrogen layer, then add another layer of soil. Repeat these layerings until the pile reaches two to three feet in height. 

Hot Composting – Maintenance

Soak the compost pile with water right after you create the heap, and continue to water the bin occasionally, keeping the overall consistency like that of a damp sponge. You want your hot compost system to stay slightly moist. Avoid an overly dry or soggy pile, knowing when to add water and when to hold off. To check your compost moisture level, stick a finger into the soil about an inch deep. If the pile is overly dry, add water. If the mixture is still damp, hold off a bit before watering.

Aerate the compost pile by punching holes into the sides, or by inserting one to two foot pieces of hollow pipe into the center of the compost. If your compost begins to stink, it’s probably because it needs more air. Try flipping the pile to remove a funky odor. Foul smells could also be caused by improper ingredients. If you added any meat, fat, or dairy products, remove them and discard them elsewhere.

Occasionally, check your pile temperature using an old kitchen thermometer or a compost thermometer (if you have one). The ideal temperature range is between 110°F to 140°F. If your compost system is not quite hot enough, add more high-nitrogen materials, such as organic fertilizer, or soft, green trimmings from your garden plants.

Once per week, or as you notice the center of your hot compost beginning to cool down, turn the pile, moving materials on the inside to the outer edges. If you would like to be able to use your nutrient-rich humus within one month, you will want to turn your compost pile every couple of days. If you need usable compost in one to three months, turn the pile every other week.

Cold Composting

Cold composting uses many of the same ingredients as hot composting, but requires less attention and a longer decomposition period. Many gardeners prefer the cold composting method because it requires much less effort and maintenance to create the same nutrient-rich garden humus that hot composting makes. The process of decomposition when using the cold composting method, however, takes significantly longer. Usable soil made from cold composting systems takes about a year to mature, and can sometimes take as long as 18 months. 

Cold Composting – Size

While hot composting requires a three to four foot cube to function, a cold compost pile can be as large or small as you like, as long as it’s not too big to stir the mixture when needed.

Cold Composting – Ingredients

• Organic materials – leaves, grass clippings (avoid weeds), soil, manure (but no dog, cat, or human waste)
• Kitchen scraps (avoid meat, dairy, and fat)
• Coffee grounds and used tea bags (tear tea bags open when adding to pile)
• Dry goods (flour, spices, crackers, etc.)
• Eggshells
• Hair
• Nutshells
• Pasta (cooked or uncooked)
• Seaweed
• Shredded paper/newspaper (avoid newspaper with color images as color ink can be toxic)

Cold Composting – Preparation

Accumulate organic materials and pile them up in your compost bin. Bury your kitchen scraps in the center of the pile to hide them from scavenger animals and insects that could disturb your compost.  

Cold Composting – Maintenance

Once a month, stir and turn the compost pile, also mixing in new organic materials that you have collected.

Warm (Hybrid) Composting

Warm composting is a nice balance between the more commonly known hot and cold methods. The warm compost pile should neither be ignored or pampered, but attended to occasionally, every two to three weeks.

Build your own warm composting system as if you were building a hot pile, but add equal parts brown and green materials, then stir and water the mixture until it is blended together perfectly. Water and turn the warm pile every couple of weeks. Allow eight to 14 weeks for the mixture to become usable in your garden beds and containers.

Each composting method has benefits and drawbacks. Which one is right for you? Well, you don’t have to know the answer just yet. Try each method out and see for yourself. Also, why choose just one? Consider trying your hand at each of these methods in order to decide which one (or more) that you prefer. After all, you can never have too much nutrient-rich soil to amend your garden with prior to each growing season, and more compost piles equals more compost.

Want to learn more about hot, cold and warm composting?

The Old Farmer’s Almanac covers How to Compost: Hot and Cold Methods

Fine Gardening covers Hot Compost vs. Cold Composting

HOTBIN Composting covers Hot Composting Versus Cold Composting

Vegetable Gardener covers Difference Between Hot, Cold and Warm Compost