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Can Compost Go Bad? Here’s What You Need To Know


Can Compost Go Bad?

Compost is a literal pile of crap and a load of garbage.

Compost is the black gold of the gardening world, and it is the prime solution to any soil problem. Because its main purpose is to heal and improve soil, it does a good job of self-correcting if the decomposition process gets off track.

Can Compost Go Bad? Despite its ingredients, it really can’t go bad. Finished, bagged compost can lose structure and nutrition over time, but this only results in a less-beneficial amendment. Compost piles have four different possibilities for going wrong, but they won’t spoil and go bad.

Today, we’re going to look at common compost issues and how to solve them.

What About Bagged Compost?

Bagged compost can smell, degrade, and lose nutritional value if allowed to sit for too long. Try to use bagged compost within a year of purchase. If it has been stored throughout the winter, you may notice the following issues.

  • Compost will continue to break down after it has been bagged. In your backyard, natural odors from decomposition dissipate quickly. In a plastic bag, these odors become concentrated and easier to identify. However, it is nothing to worry about, and you can still use bagged compost that has begun to smell.
  • As bagged compost breaks down, it will lose volume. This is normal and completely harmless. The compost will lose some structure and become denser, but it is still a perfectly acceptable soil amendment. If you are trying to help alleviate drainage problems, try mixing in some new compost to help with structure.
  • Finally, as compost sits, it will leach nutrients. Sometimes, you will find a dark liquid at the bottom of the bag; this is a highly-nutritious byproduct called leachate. Don’t toss it out! Pour it on a nearby tree or tomato plant for an extra boost. The leachate will contain nutrients that have leached out of the compost. However, even with lower nutrient content, compost is a valuable soil amendment because it improves structure.

Why Does My Compost Pile Smell?

If compost stinks, something is out of balance.

If you prefer to make your own compost, you may have a few issues with the decomposition process. However, they are easily corrected, and do not harm the final product.

There are two reasons a compost pile might smellOpens in a new tab., and both can be solved by turning your pile.

If your compost pile smells like a garbage can, it has developed anaerobic conditions. This simply means there is not enough oxygen in the pile, so harmful bacteria have taken over.

Find some large twigs and layer them a few inches thick next to your pile. Next, turn your pile over onto the sticks. The new bottom layer will help provide oxygen from the bottom, and turning the pile will introduce oxygen into the center.

Anaerobic conditions form when layers are too packed to allow airflow, so avoid solid layers of shredded newspaper, cardboard, and grass clippings, and turn your pile more often.

If your compost pile smells like ammonia, it’s too rich in nitrogen. This can happen when the ratio of brown to green is too low.

The solution is to incorporate more brown material, which is easily achieved by turning the pile. Gather shredded newspaper, cardboard, dead leaves, straw, and other carbon-based organic materials. As you turn the pile over onto a new section of ground, incorporate brown material to help balance the pile.

Why Won’t My Compost Pile Heat Up?

This depends on how you built your pile to begin with. A lack of heat means decomposition has either slowed or stopped.

Compost has four requirements to stay hot, or active:

  • Adequate Oxygen
  • Adequate Moisture
  • A 2:1 Ratio of Carbon to Nitrogen
  • Beneficial Microbial Activity

If the first three requirements are met, then healthy microbial activity will be the result. You will know microbes are active because the pile will heat up. If the pile is not heating up, it means there is no microbial activity, which means at least one of the first three requirements is not being met.

For more information on Active Composting, read my Complete Guide To Active Compost.

A lack of oxygen will probably cause the pile to smell bad, unless there is also a lack of moisture. Oxygen deficiency can be caused by thick layers of material that matt together. It can also occur when piles are built on a non-porous platform, like plastic sheeting. Turning the pile and adding bulky brown material can help fix this issue.

A lack of moisture will cause the pile to feel dry, which sounds simple but may be deceptive. The tops and sides of piles can dry out easily in hot or windy conditions, but the inside of the pile has an ecosystem all its own.

To truly diagnose a lack of moisture, you need to look at the center of the pile. If it is moist, then you have a moisture retention issue. If it is dry, you likely have an issue with your ingredients.

Moisture retention can be solved by turning the pile and adding shredded newspaper or cardboard. As you turn the pile over, add in new brown material and soak it thoroughly. Water the pile every few days in hot, dry weather.

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If it is your ingredients that have the issue, you likely added too much brown material. Cardboard, sawdust, and paper can hold water well, but if there is a lack of nitrogen, decomposition will slow and the pile will dry out.

This can be solved by turning the pile and adding more green, or nitrogen-rich material, such as grass clippings and vegetable scraps. Water the pile thoroughly, and continue to water it every few days when it is hot.

If your pile smells fine and retains some moisture, but won’t get hot, you are lacking nitrogen. Again, this can be solved by turning the pile and adding new material. Ingredients high in nitrogen include manure, grass clippings, vegetable scraps, and herbaceous prunings. If the pile was moist, you do not need to water it as you add new material.

One rare but possible reason for an inactive pile is a complete lack of microbial activity. If you have tried all other methods to restart your pile and they aren’t working, throw a handful of finished compost in the center of your heap and give it a few days.

The microbes should begin to multiply and restart the decomposition process. Lack of microbial presence only happens when piles are isolated from the soil, such as being built on plastic sheeting or concrete.

Why Does My Compost Pile Have Bugs?

Bugs in a compost pile are totally normal. In fact, many are beneficialOpens in a new tab.. Or, at the very least, harmless. Fruit flies, ants, termitesOpens in a new tab., and beetles are common.

The only “bad” insect for compost piles is flies, and they aren’t even bad for your compost. They are simply an indicator that something in your pile is wrong. Because flies need moist conditions to reproduce, flies will generally signal wet, anaerobic conditions, and you will probably notice an odor.

Just follow the steps for fixing anaerobic conditions, and the flies will take care of themselves.

Whether you make your own compost or buy it in bags, it’s almost impossible for it to spoil. If in doubt, use it anyway. Once compost is in the soil, it will break down just fine, and cause no harm to your plants.

If you’re new to composting, check out our article on active compost piles to get started.

Related Questions

Can I use compost if it has been exposed to chemicals?

It depends on the chemicals. If you live in an agricultural area, you should be aware of the chemicals that are sprayed around you. Some may be herbicides, which target and kill specific kinds of plants.

Depending on the nature of the chemical, some may survive the composting process and harm plants once you incorporate it into the soil. If a toxic chemical has been spilled onto your pile, it is probably best to discard it and start over.

Can I use compost that has mold in it?

Yes. Mold can begin to grow in anaerobic conditions, but it is usually just a symptom of a pile that is a little too wet or doesn’t have quite enough ventilation. The good news is that as soon as you put compost into the soil, those wet, anaerobic conditions disappear.

The soil will provide proper conditions for decomposition, and the mold will simply die and be decomposed along with the rest of the material.

Why is my compost slimy?

Slimy compost is a result of anaerobic conditions. Spread it out to allow it to dry, and then pile it back up with new ingredients and soak it lightly. If the problem continues, consider the ingredients you used and try adding more bulky materials.

Sydney Bosque

Sydney has over 15 years of experience in lawn maintenance, landscape design, and organic gardening. She has an A.A.S. in Landscape Design/Organic Produce Production from the Nebraska College of Technical Agriculture.

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