The Complete Guide to Active Compost

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There are two different composting strategies, and they have much more to do with your personality type than they do with desired outcomes.

If you want to be able to throw garden waste into a pile and one day, maybe, use it as a soil amendment, then you should skip this article. Any organic material, given enough time, will decompose. Just throw it all together and be patient. That, essentially, is cold composting.

Hot, or active composting, is a method that takes all factors of decomposition into account and creates an environment that is constantly fueling the process to produce compost in a short amount of time.

You are essentially building the ideal conditions for microbial activity, which will generate heat and speed up decomposition. It’s like baking a humus cake; it will need consistent mixing and monitoring.

What Are The Benefits Of Active Composting?

Maintaining an active compost pile can be time-consuming, but it’s worth the effort if you’re serious about improving your soil and keeping organic waste out of landfills.

Active composting gets faster results because you’re maintaining an ideal environment for decomposition. Microbes will break down organic material quickly if they have adequate moisture and oxygen available.

While a cold, or passive, compost pile can take over a year to fully decompose, active compost piles can break down in less than a month.

Active composting can kill weed seeds due to the pile reaching temperatures of up to 180° internally. Passive compost piles do not reach these temperatures, so weed seeds either lie dormant or germinate in the pile.

If you want to compost weeds that you have pulled or plants that have bolted, hot compost should kill the seeds so you don’t spread them throughout your garden and cause more work.

Active composting can kill diseases that linger on dead plant material. Diseases like blight or botrytis can lie dormant in dead plant tissue, and if the compost does not get hot enough, those diseases can infect other plants.

If you want to compost disease-prone plant material, like tomato vines or potatoes, active compost piles are the safest option.

Active composting can break down tough materials like cardboard and twigs. All compost piles need a mixture of carbon and nitrogen-based ingredients in order to decompose properly.

However, it can take a long time to break down tough materials like hardwood prunings and old Amazon boxes in a passive compost pile. Active compost can break down these materials much quicker.

What Can I Put In An Active Compost Pile?

Hot compost piles can break down a variety of materials very quickly. These include, but are not limited to:

• Rotting vegetables
• Newspaper
• Cardboard
• Twigs
• Grass clippings
• Leaves
• Manure
• Coffee grounds & tea bags (but tear them open first)
• Weeds
• Eggshells

Also, it’s important to keep things out of a compost pile that will attract wildlife, cause disease, or simply won’t decompose. Do not add the following materials to your compost pile:

• Meat, raw or cooked
• Weeds that have been sprayed
• Stickers on produce
• Glossy paper
• Styrofoam
• Paper plates & cups
• Invasive weeds

Many materials, like bread, nut shells, and orange peels, will decompose given enough time. However, they attract rodents and can make it difficult to maintain active decomposition.

They can also take a long time to break down. Some items, although they are biodegradable, are just not worth the time.

How Do I Build A Hot Compost Pile?

One major difference between passive and active compost is that active compost requires all the ingredients up front. Before you begin an active compost pile, you will need enough material to fill a 4’ cube.

Two-thirds of your material should be brown, or carbon based. This includes twigs, cardboard, paper, and dead leaves. Twigs should be put on the bottom to help with air flow.

One-third of your material should be green, or nitrogen based. This includes green leaves, produce, grass clippings, manure, and coffee grounds.

Before you build your pile, make sure your materials are crushed, shredded, or ripped as small as you can get them. This creates a larger surface area for microbes to break down the material, which results in faster decomposition and higher temperatures. This is especially important for brown ingredients.

Once you have all of your material ready, it is time to start layering. Start with a bulky, brown layer, as this will help the pile to breathe. Then, alternate green and brown layers, with the brown layers being double the thickness of the green layers. Top it all off with a layer of brown material, and your compost lasagna is complete!

If you want a more uniform look, you can build a compost bin or fence to hold your pile. There are pros and cons to compost bins, but for active compost, you may find them to be a hassle.

Since you will be turning your compost regularly, easy access is a must. Bins are nice for passive compost piles that may sit for over a year, but since active piles decompose so quickly, you may not need a long-term holding area for them.

How Do I Maintain A Hot Compost Pile?

Once you’ve built your pile, the real work begins. Maintenance is what separates a hot compost pile from a cold one.

Active compost piles will need turned every few days. Buy a compost thermometer to record internal temperature, and check it daily. As the pile begins to decompose, the temperature will rise. After 3-4 days, the temperature will begin to fall. This is your sign to turn the pile.

Turning a compost pile is easy if you don’t use a compost bin. Simply take the entire pile and turn it over onto an adjacent spot in the garden. 

The main reason for turning is to incorporate oxygen into the pile and prevent compaction. Too little oxygen will slow down or halt decomposition.

Once you’ve turned it, reinsert the thermometer and wait for the temperature to climb again, signaling decomposition, and then for it to drop, meaning decomposition is halting.

You should expect temperatures to rise to 140°-170° before dropping. Once it drops to 130°, it’s time to turn. 

Moisture is key to maintaining a compost pile, so you should water it as needed to keep it damp.

• Too much water will drop the temperature and could stop the process.
• Too little, and the microbes will die from lack of moisture.

In extremely hot or dry climates, you may need to put a tarp on top of your pile to prevent evaporation. Aim for the same water content as a damp sponge.

Keep turning your compost every 3-5 days until it has fully decomposed.

How Do I Know When Compost Is Ready?

Your compost is ready to use when you can no longer distinguish individual ingredients. It should look and feel like a healthy, loamy soil.

Compost piles shrink to about one-quarter of their original size, so even if the materials seem to be broken down, wait until you see adequate shrinkage before declaring your compost ready to use. When you add organic material into the soil that has not decomposed, it will pull nitrogen away from plant roots

 to finish the process. So, adding unfinished compost to your garden or landscape will do the opposite of what you’re trying to do; it will tie up the most essential nutrient for plant growth.

Finished compost should smell sweet and earthy, so before adding it into your garden or landscape, take a handful or two and give it a sniff. If there is a hint of garbage odor, turn the pile and allow it to sit for another week. It may be lacking oxygen.

Inspect your compost for pests before incorporating it into your garden or landscape.

That’s it! Once you are confident in your compost, you are the horticultural equivalent of a gold miner. Compost is the black gold of gardening, and producing your own is a great step towards sustainability.

Check out our articles on soil improvement for how you can incorporate compost into your lawn and garden to solve many soil issues.

Related Questions

What if I forget to turn my compost pile?

Don’t worry. Maintenance is the key to hot compost piles. If you stop doing maintenance, it just becomes a cold compost pile. You can always restart the process by turning the pile and adding some moisture.

What if my compost pile doesn’t get hot?

Moisture and oxygen are the two vital ingredients for high temperatures in your compost pile. First, make sure your pile is damp, but not too wet. Then, turn it and wait a few days to see if aerating it brings the temperature up.

If not, you may have an imbalance of green and brown material. Too much of either can slow down the process. Unless you’re composting potato or tomato vines, or your pile has weed seeds, cooler temperatures are fine. But, it will take longer for the compost to finish.

Do I need lots of different ingredients to make compost?

No. There are two benefits to compost. The first is nutrients. Different organic materials have different nutrient profiles, and a variety of ingredients will produce a more balanced compost.

The second benefit is structure. Compost, regardless of nutrient content, will improve soil structure. If you are trying to improve clay soil, or sandy soil, or any other structure problem, you do not need a huge variety of ingredients.

For a garden application, a variety of ingredients would be beneficial, but not necessary.