Do You Need Compost if You Already Used Fertilizer?

Many people get confused between compost and fertilizer because they have similar qualities. However, they are different substances that have different functions. So, you may be wondering if you need compost if you’ve already used fertilizer.

You might need compost if you already used fertilizer, depending on the soil. If the soil doesn’t need to be amended and is suitable for growing plants, you won’t need to add compost. However, if you’ve used fertilizer and the soil condition needs to be amended, you’ll need compost.

Understanding the differences between compost and fertilizer is essential to maintaining a happy garden. This article will discuss their differences and whether they’re safe to use together. Keep reading to learn more.

Can You Use Fertilizer in Place of Compost?

You can’t use fertilizer in place of compost because it has different functions. While fertilizer’s primary purpose is to add nutrients to the soil, compost’s primary function is to amend the soil. However, compost also contains nutrients, so it is helpful if you want to feed the soil.

In many cases, you can use fertilizer and compost together to create the best results for your soil, plants, and garden.

Key Differences Between Compost and Fertilizer

Although many believe compost and fertilizer are the same, they have plenty of differences and shouldn’t be used to replace one another. Before you prepare your soil, it’s essential to understand the differences between compost and fertilizer. This will help you know which ones you’ll need to use.

Below, let’s look at the primary differences between them:

Compost Consists of Organic Matter

One of the most significant differences between compost and fertilizer is what they’re made of. While fertilizers are generally made from chemicals like phosphorus and nitrogen, compost consists of organic matter, including the following:

  • Food leftovers (fruit peels, for example)
  • Leaves and grass
  • Branches and sticks

Since compost is fully organic, you can make it at home. On the other hand, it’s generally not possible or common to make fertilizer at home. The only way to get fertilizer is to buy it from a gardening retailer.

Compost Helps Soil Retain Moisture

Unlike fertilizer, compost helps the soil retain moisture. This is particularly useful if your soil is dry and loses water quickly. This isn’t bad for your soil, but it can be detrimental to plant health. Compost helps because it works as a natural and organic soil amendment—you can’t say the same for fertilizer.

So, if you’ve used fertilizer but your soil doesn’t retain moisture very well, using compost could help.

Compost Amends All Types of Soil

Whether the soil is sandy or clay-like, compost will be beneficial. It works well for sandy soil because the compost clings or clumps together, which helps cover any air holes that may be present due to the light sandiness of the soil. It also helps your sandy soil retain water, making it a better environment for plants to grow.

Adding compost to clay soil helps break it down, making it lighter, looser, and easier to manage. It also enriches the soil and gives it nutrients, but this isn’t specific to clay soil. Compost will feed the soil nutrients and make it a more favorable environment for all plants, no matter what kind of soil you have.

Fertilizer doesn’t help amend different soil types. If you have clay soil that you want to improve and loosen up, fertilizer won’t help. Compost, however, will. 

Fertilizer will give your soil nutrients, so you can use it along with compost. In some cases, compost may slightly reduce the need to use fertilizer because it already contains plenty of nutrients. 

Using Too Much Fertilizer Damages Plants

Fertilizer burn can occur when you apply too much of it to the soil. This is detrimental to the plant roots and can cause premature death in your plants. Since fertilizers contain chemicals, it’s essential not to use too much.

While using too much compost can also damage your plants, it’s less likely to cause damage as severe as over-fertilizing. Therefore, you need to be especially careful when applying fertilizer.

Compost and Fertilizer: The Main Similarity

I’ve discussed the main differences between compost and fertilizer, but it’s also essential to know the main similarity. 

In rare cases, using compost in a garden will reduce the need to use fertilizer. However, this depends on your soil and its needs. 

To better understand if you should use compost and fertilizer together (or one instead of the other), let’s look at the primary similarity below:

Compost and Fertilizer Both Provide Nutrients to the Soil

One of the main similarities is that both products provide the soil with essential nutrients. While fertilizer offers these nutrients in chemical form, compost provides them in a more natural and organic form.

Fertilizer and compost both contain the essential nutrients for soil and plant health:

  • Nitrogen
  • Phosphorus
  • Potassium

So, if you’re looking for something to add nutrients to your soil and don’t need anything else, you could use either compost or fertilizer. 

An example of compost that would benefit soil is banana peels. This is because banana peels contain plenty of nutrients, including potassium and phosphorus. Fertilizer also contains these nutrients, but banana peels are cheaper. Using them as compost also encourages a waste-free lifestyle.

Are Compost and Fertilizer Safe To Use Together?

Compost and fertilizer are safe to use together because they have different beneficial functions. While compost and fertilizer both add nutrients to the soil, compost also helps improve the soil conditions by helping sandy soil retain moisture and loosening clay soil.

Fertilizer doesn’t help improve these kinds of soil conditions, so you can’t and shouldn’t rely on it as a soil amendment material. Therefore, if you’ve already used fertilizer but the soil isn’t the right consistency, compost is entirely safe to use. Not only is it safe, but it’s an excellent idea!

However, it would be best to exercise caution. Be careful not to use too much of either product, particularly fertilizer. Since compost and fertilizer contain plenty of nutrients, adding too much of them can seriously harm the soil and negatively affect the plants. 

So, the products are safe to use together as long as you don’t overuse them.

Is Compost Necessary for a Garden?

Compost is necessary for a garden if the soil needs an amendment and some added nutrients. However, if the only thing the soil needs is some nutrients, most gardeners will use fertilizer alone. 

Adding compost to your garden is never a bad idea, whether you’ve already used fertilizer or not. Even if it’s not entirely necessary, it’s a good idea to use it.

Here are some of the main benefits of compost in a garden:

  • Compost improves soil fertility.
  • It improves all kinds of soil types.
  • It gives nutrients to the soil and plants.
  • It’s natural and eco-friendly.
  • Compost is easy to make at home.

With all the benefits of using compost, there’s no doubt that it will help enhance and improve any garden.

Is Fertilizer Necessary?

Fertilizer isn’t necessary if your soil already has the nutrients it needs. To know whether your soil needs fertilizer, consider conducting a soil test. Another indicator that you don’t need fertilizer is if your plants always grow with no issues. 

In other words, you shouldn’t try to fix something that doesn’t need to be fixed.

It’s important to remember that nutrients occur naturally in the soil, so it’s not always necessary to use fertilizer. However, whether or not you should use fertilizer will also depend on the plants in question. Some plants require nutrient-rich soil at all times, whereas others can thrive in soil that isn’t as nutrient-rich.

Understanding your soil and its needs will help you determine whether fertilizer is necessary. In most cases, applying fertilizer now and again won’t cause damage to your soil. However, it’s a bad idea and highly unnecessary to apply fertilizer too frequently and in high amounts. 

As discussed earlier, this can result in fertilizer burn, which you always want to avoid. Not only that, but it’s wasteful and an unnecessary expense.

How Often Should You Apply Compost to the Soil?

You should apply compost to the soil once every 1-2 years for the best results. Using it more than once per year is unnecessary. You can apply compost to the soil at any time during the year because it helps keep the soil in favorable conditions, no matter what the season is.

Even though you can technically apply compost at any point during the year, it’s good to use it a few months before summer so that it has time to settle. However, applying it at any point is acceptable, and it will still be beneficial to the soil and plants.


You don’t necessarily need compost if you’ve already used fertilizer, especially if the soil doesn’t need to be amended. However, if the soil is too sandy or clay-like, adding compost will be beneficial.

Since fertilizer can’t amend the soil, it’s often best utilized when combined with compost. This also means you can’t replace fertilizer for compost and vice versa.

There are many differences between compost and fertilizer. Some of them include:

  • What they’re made of
  • Affordability
  • Their main functions

Fertilizer feeds the soil; compost feeds and amends it.

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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