Is Compost Bad for Certain Plants?

Compost is a great resource that people all over the world use to provide much-needed nutrients to their gardens. While most of the composting conversation talks about what you can and can’t add to your compost, we are instead going to talk about what you maybe shouldn’t add your compost to once it is ready. 

Compost is good for every plant out there except healthy grass, but it can become bad for plants if you aren’t careful. Using too much compost or using it before it fully decomposes can harm your plants rather than help. So, compost is good for all plants unless we make a mistake with the compost. 

So, let’s discuss in more detail when compost may not be the right choice for your plants. 

When To Avoid Using Compost

While most of your plants will welcome the nutrients that compost offers, it is not always a good idea to use compost in every situation. While there are no specific plants that have an aversion to compost, there are situations where it may hurt rather than help. 

When the Compost Isn’t Fully Processed

One of the riskiest ways of using compost is to use it before it has finished processing. During the composting process, microorganisms will decompose your pile until they have filled it with nutrients that can help your plants, but adding it too soon can actually do the opposite. 

During the composting process, those microorganisms work hard to decompose all that material, and they need all the help they can get. Without proper nutrients, those microorganisms will work slower or stop working at all. So, they feed off nutrients that are in the pile or nearby. 

This means that compost you spread before it is ready will still need nutrients to thrive and will take them from whatever source is available. Your plants will suffer if exposed to unfinished compost because the microorganisms still working on decomposing the compost heap will use the nutrients from your plants to do it. 

Most stories you hear about gardeners whose compost killed their plants come from a pile that is not ready yet. So, the importance of only using compost that you allow to decompose completely can’t be understated. If you need help with understanding when your compost is ready, check out this article for a helpful guide: How to Test Your Compost to Know If It’s Ready

When the Grass Is Too Green

You should avoid using compost on your grass if it is already healthy. The reason for this is that the grass will continue to absorb nutrients from your compost even though they are not necessary. This oversaturation will cause brown and yellow spots and can make your grass a lot less healthy overall. 

It is common for some to use compost to help patchy grass grow healthier. So, adding some compost to your lawn may seem like a good idea. Since grass gets oversaturated so easily, it is not a good idea to add compost to already thriving grass. 

While compost is not bad for grass overall, it is certainly not going to help already thriving grass. So, don’t use compost on your lawn if it is already healthy. Otherwise, you may just make it unhealthy. If you want more details about using compost on your grass, check out my other article: Is Compost Bad for Grasses?

When You Use Too Much 

Another risk that many gardeners don’t consider when using compost is that you can use too much at a time. Unfortunately, when it comes to composting, too much of a good thing isn’t actually a good thing. Overexposing your plants to nutrients in compost can cause deficiencies in other areas of nutrition. 

As we discussed with grass above, some plants will also continue absorbing nutrients from your compost even when they reach sufficient health. This means that you can overdo the compost you add to the soil, and it is also the reason that gardeners recommend using a combination of soil and compost for your plants. 

So, let’s talk about what specifically too much compost can do to your plants. If your plants take in too much ammonium from your compost pile, it can cause them to take in more calcium, magnesium, and potassium to compensate. Unfortunately, these nutrients can increase the overall pH of the plant. 

Iron Deficiency

Once the pH of the plant is too high, certain nutrients become less available to the plant. High pH can cause your plant to become nutrient deficient in many areas, especially iron. When plants develop iron deficiency, this can cause yellowing of leaves or Iron Chlorosis. 

Iron Chlorosis can represent differently in different plants. Sometimes it will cause your plant’s leaves to turn white or brown instead of yellow. In other instances, these symptoms may not present at all. In fact, Iron Chlorosis may be affecting your entire garden, but it may only show symptoms in just a few plants. So, it can be difficult for you to spot. 

Iron deficiency in your plants can cause a lot more than just discoloration of leaves. In fact, it is common for plants with Iron Chlorosis to develop growth and overall health issues. If the issue persists over an extended period, it can kill your plant completely. In plants that produce fruit, you may notice that the fruit is smaller than anticipated or tastes bitter when eating it. 

Simple Solutions if Compost Is Harming Your Plants

Since we discussed the specific examples of how compost can be bad for your plants, let’s talk about what to do if this occurs. First, there is the common problem of an unfinished compost pile. Our article linked above can help you figure out whether or not your pile is ready, but here is what to do when you have already made the mistake of adding it to the soil. 

Most of the compost materials that take the longest time to decompose are sticks and other similar chunky materials. So, if you have already added your unfinished compost to the garden, you can help by removing these chunky parts of the compost. In many cases, most of the compost pile will finish decomposing while the chunky materials take longer. 

So, removing those chunky materials can prevent the microorganisms from taking nutrients from your plant to help decompose the large parts. This may not completely fix the problem, but removing those chunky parts will allow your compost to finish composting the remaining material quickly, if necessary. 

Finally, let’s talk about using too much compost. The obvious fix for this problem is to use less compost, but let’s go further. If you have already used too much compost and are worried about a potential iron deficiency, you should test the pH of the soil. If you are familiar with his process already, then you’ll know it is not particularly difficult. If not, let’s talk about it. 

The easiest way to test the pH of your soil is to buy a test kit. They’re very affordable, and you can find them in most stores with a decent garden section. These test kits can tell you exactly what the pH level of your soil is without waiting for symptoms of Iron Chlorosis or trying to guess. 

These tests are also helpful in determining the pH levels of plants when they require a different level of acidity compared to others. While most plants do just fine at the average soil pH levels, some plants, like blueberries and azaleas, require a lower pH. So, having these tests available for your garden when you need them is never a bad idea. 

Final Thoughts

While every plant will appreciate the nutrients that compost can provide, it’s important to be careful when using it. Besides healthy grass, no plants have an aversion to compost, but that doesn’t mean it can’t harm your plants if you aren’t careful. 

If you want the compost to help your plants and negate the risk of killing the plant, always make sure your compost is ready and don’t use too much. By following these rules, your compost won’t harm your plants. If you notice changes in the health of your plants after using compost, consider these options and adjust accordingly.

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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