Many call it black gold.
That’s how wonderful they think compost is for your plants.
But can you add too much compost? Will it hurt your plants?
Too much compost can hurt your plants because it contains high amounts of nitrogen, phosphorus, and potassium. When these nutrients build up in the soil, it can become toxic for the plants. This can cause wilting or stunted growth.
In this post, I’ll help you learn what too much compost does to the plants. I’ll also show you what are the signs of too much compost and how to avoid this. I’ll give some tips on fixing the problem if you used too much compost.
Can too much compost hurt plants?
Getting the right amount of compost is important. But is it possible for you to use too much, risking damaging your plants? To understand this, we need to know how it affects the soil.
Compost is often high in important nutrients. Most commonly, it contains plenty of nitrogen and phosphorous. In small doses, this is good. The plants need these nutrients present to grow strongly. Nitrogen doesn’t build up in the soil. The rain will wash away it.
But this isn’t the case with phosphorous. It will move through the soil at a slower rate. Often, it will only move one inch a year. Because of this, continually adding new compost will cause the phosphorous to build up over time. Eventually, high levels of phosphorous can become toxic to plants.
Can compost burn your plants?
Compost can burn your plants if it contains high amounts of nitrogen, phosphorus, and potassium. The excess nutrients burn the roots of the plant that will stunt their growth and affect the foliage.
Here are some actions that you can try to treat compost burns:
- Scoop off excess compost. This stops more nutrients from leaching into the soil, compounding the problem.
- Apply plenty of water. This will wash away any excess nutrients. Make sure you are catching the water, rather than allowing it to run off and contaminate other waterways. This nutrient-rich water is responsible for dangerous things like algal blooms.
- Move the plants. This is the last resort. But sometimes the phosphorous levels have become so high that it is the only option. Over time, these levels will naturally reduce, so you can start planting in the area again.
As long as you catch it early, your plants shouldn’t be too seriously affected by burns. But the longer you leave them, the lower the prospect that your plants will recover. We’ll discuss some ways you can deal with high phosphorous levels a little later.
Can you put too much compost on a plant?
You can put too much compost on a plant which will raise the level of nutrients in the soil. The excess nutrients like nitrogen, phosphorus, and potassium can affect the roots and foliage of the plant.
This is about more than just raising NPK levels, though, too much compost has the potential to smother plants. Here, it will form such a thick layer that water won’t be able to get through. Sometimes, this nutrient-rich runoff can cause problems. For example, it might cause algal blooms in the local waterways.
The best way to stop this from happening is by taking preventative measures. As we’ll discuss later, you won’t need to put on a lot of compost to see the benefits. As long as you are applying a sensible dose, it’s unlikely that you will see any issues.
What are the signs of too much compost?
Normally, when adding compost to plants, you would expect them to thrive. But this won’t always be the case. If you add too much compost, it can have the opposite effect. Your plants can shrivel and die. There are a few signs that you might have burned your plants. These include:
- Yellowing or browning of the leaves
- The plant might wither
- Stunted growth
- Lack of mycorrhizae. We need these for the plants to absorb water and gain nutrients from the soil.
There is an easy way to test whether these problems are occurring because of the high amount of compost in the soil. You can do an NPK test. These are available at most hardware stores and allow you to accurately determine how much phosphorous is in the soil.
The ideal amount of phosphorous will vary depending on your soil type and the plants you intend on growing. Between 25 to 50 ppm is considered healthy. Once it starts to get over 60, it can become a problem.
How do you fix too much compost?
Like most things in the garden, there are many ways that you can overcome the problem. First, you shouldn’t put any more compost in the area.
This gives it some time for the chemicals to naturally disperse. How long this can take will depend on how high the phosphorous levels are. For example, if it is between 150 to 200 ppm, it can take around three years to correct the problem.
You might also want to consider the type of plants that you are using. It can be a good idea to plant some that will increase nitrogen, without boosting phosphorous levels. Some good choices are beans and peas.
Finally, you will need to spray zinc and iron. We need these to keep the plants in this part of the garden healthy. You’ll need to use a spray that has these nutrients at one percent. Spread this throughout the affected part of the garden once every four weeks.
How much compost to add to soil?
The purpose of this article isn’t to convince you to avoid compost. Rather, it is to point out that it’s best to use it in moderation. There are a few ways that you can apply your compost.
First, you can add the compost to the soil. Here, you will only need one to two inches. This will need to be blended with the rest of the soil. As you are doing this, monitor the NPK levels, stopping if the amount of phosphorous gets too high. Compost releases nutrients slowly, so you will only need to add it twice a year.
The other option is to soak the compost in water. Here, you will need to use one part compost for every three parts of water. Then, you can sprinkle this in your garden. This is gentler than applying compost directly to the soil. But you will need to apply it more frequently. If you make up a large batch, it can last for a few weeks.
You can even use compost as part of a homemade potting mix. Here, you will need to follow a simple recipe. Get four parts of compost with one part sphagnum moss and two parts of coarse sand. Once you have the ingredients, you just need to throw them into a wheelbarrow and mix them.
Here are some of my favorite container gardening tools
Thank you for reading this post. I hope it helps you with your gardening needs. I’ve listed some tools below that can help you with container gardening. These are affiliate links so I’ll earn a commission if you use them.
Gardening Gloves – I find the Pine Tree Tools Bamboo Gardening Gloves really good for both men and women. It’s made from bamboo so helps absorb perspiration. They are also comfortable and fit very well.
Containers – You know picking the right container is crucial for your container gardening. I’ve written a detailed post on the best containers you can choose from. If you’re happy with a plastic container, you can check out the Bloem Saturn Planter.
Watering Can – This is a must-have tool when you’re growing plants in pots or grow bags. It helps to water the potting soil without splashing on the foliage. The Kensington Watering Can is stylish, strong, and can provide precision when watering potted plants.
Trowel – Garden Guru Trowel is my favorite because it’s durable and comfortable to use. My gardening friends really love having a trowel because they use it for digging soil, mixing fertilizer, moving seeds, leveling out the soil, mixing compost or mulch, and also dividing tubers
Bypass Pruner – I really like the Corona Bypass Pruner because it’s durable and gives a clean cut that helps plants recover faster. If you’re looking for something cheap, get the Fiskars Bypass Pruner that is really good as well.
To see an extensive list of the best container gardening tools gardeners recommend, check out this resource that I made for you.
Kevin is the founder of Gardening Mentor, a website that aims to teach people to grow their own food in a limited space. As a self-taught gardener, Kevin has spent several years growing plants and creating gardening content on the website. He is certified in Home Horticulture and Organic Gardening by expert gardeners from Oregon State University.