How Much Compost to Add to Raised Garden Bed

There are many benefits to choosing a raised garden. Whether you are doing it because it’s essentially easier than a garden in the ground or you simply have to because you live with a concrete backyard, there is one thing to keep in mind: the soil is key to happy, healthy, and thriving plants, and you won’t get the same results without a bit of compost.

How much compost do you add to a raised garden bed? When adding compost to your raised garden bed, you need to be extra careful. The compost shouldn’t take up any more than 30% to 50% of your soil. The rest should be mostly topsoil with a pinch of potting soil to let the soil ‘breathe’ a bit.

If you are new to the raised garden community and want to get started the right way, then you need to know the ins and outs of compost. There is quite a lot more to it than simply opening up a bag and tossing it into your soil whenever you please. There is a right way and a wrong way to go about compost, and we’re going to cover all that and more in this post.

What is a Raised Garden Bed?

A raised garden bed is essentially just how it sounds: a garden that is raised off of the ground by means of three-to-four foot wide containments. They are typically made of materials including wood, concrete, or rock. The overall length and shape can change according to the gardeners’ specific needs and wants.

These types of gardens are best used by those who don’t have a good spot in their yard to grow a garden or simply don’t want to hassle with plowing something into their ground. Whether raised or planted directly into the ground, one thing that is needed for success is compost.

What is Compost, and Why Do You Need It?

A word that may sound like a ‘buzz’ word in gardening is compost. You’ve heard it on all of the gardening television shows, seen it as you walk through Lowes, and even overheard your neighbor raving it about it to her best friend. But what exactly is compost, and is it necessary to add to your garden?

Referred to as ‘Black Gold’, compost is a collection of decomposed organic matter. This matter is added to your soil to promote the microbe production of the soil. These microbes aid in plant growth significantly, which is why any garden that includes compost will be a healthier garden in the long run.

There is a seemingly endless amount of benefits that go hand-in-hand with using compost in your garden. Here are a few great reasons why you should see this product as a necessity, rather than a luxury:

  • Compost enriches the soil. As previously mentioned, the compost is responsible for producing microbes in the soil. This, in turn, means more nutrients and overall plant growth in your garden. That is the main goal after all, isn’t it?
  • Compost helps to retain moisture. Since compost is a bit denser than regular topsoil, it can hold onto moisture for a longer period of time. This allows your plants to be hydrated without the worry of drying out. While you still need to water your garden regularly, your plants likely won’t fall into a dire situation anytime soon.
  • It works to suppress plant diseases. Many plants, especially tomatoes and other vegetables, are highly susceptible to diseases. Their root systems can be finicky and, without proper precautions, they can end up diseased and destroyed. But compost works to protect the roots of these plants and keep them strong, fighting off diseases coming their way.
  • There is less worry about pests invading your garden. The compost also makes sure that no pesky creatures end up chewing away at the roots of your plants. Creatures like worms and crickets who might find your plant a tasty treat will be kept away by the compost.
  • It allows for more organic growth. Not wanting to use chemically-infused fertilizers to keep your garden up-and-running? We don’t blame you. Unfortunately, though, it’s the best way to make sure there’s no pests or diseases following your garden. But with compost, you can say goodbye to chemicals and enjoy organic, natural protection.
  • It encourages bacteria and fungi production. While this might not sound like the greatest thing, it’s nature at play. The bacteria and fungi that are produced by compost will work to create another type of organic matter known as humus. This is a material that is jam-packed with essential nutrients for your plants, thus creating an even more nutrient-dense area.
  • It helps the environment. If there is one thing that is on everyone’s minds these days, it’s saving the planet. Well, you can do your part by using compost and help to lower your overall carbon footprint on the environment.

As you can see, compost is a critical part of growing a successful garden. It creates an environment that allows your plants to thrive with nutrients while shooing away pesky insects and creatures and diseases that may want to come in the way.

This step-by-step video is a wonderful tutorial for making your own compost.

What Type of Compost is Best for a Raised Garden Bed?

There are two types of compost: homemade and store-bought. While there is nothing specifically wrong with buying store-bought compost, you won’t get the same organic, ready-to-use material that you would get from creating your own.

There are, however, several wonderful store-bought composts you can use if you do not have the time or desire to make your own. Keep in mind that it can take months to make your own homemade compost, and some people may find the time and dedication necessary for creating this handy ‘Black Gold’ to be too much work.

However, if you are ready and willing to try your hand at making your own compost, there are a few simple steps to follow:

  • Find an area to create your compost. Many people find that using a trash bin or another type of very large bin will do the trick. In fact, some gardeners simply opt to place their compost directly on the ground. This allows other items, like worms and insects, to add nutrients to the compost during the decomposing period.

The main goal here is to find a big enough space to hold your materials. It’s decomposing organic matter, though, so you don’t need to find anything too fancy.

  • Add your material. Your next job is to add in the material that will make the compost. The equation for successful compost is equal parts of green and brown material. As far as green material is concerned, you can use things like leaves and grass clippings. Brown material can include fruit peels, wood, and twigs.

Whatever you decide to add to your compost, make sure that there are equal parts. You must have equal parts of nitrogen and carbon, so balance is crucial. It’s the most critical part of creating compost, so handle this step with great care.

Tip: You want to avoid adding fish, dairy, and meats to your compost, especially if it is being kept outside. Rodents and animals, such as dogs and raccoons, will be attracted to the smell and may end up ruining your compost.

  1. Add some moisture. Keeping your compost damp is an important part of decomposition. With too little water there won’t be enough moisture to kickstart the decomposition process, while too much water will drown your materials into a soggy, useless mess. That being said, just add a pinch of water so that the organic matter appears damp.
  1. Turn the pile of organic material every week or two. Leaving the compost in one spot will not allow for the organic materials to ‘activate’ and decompose properly. You should make sure to turn your compost every week or two using a shovel, a pitchfork, or even your own hands. At this time, you can check to see if the material is still damp.
  1. Wait a few months for the decomposition to take place. It will take a few months before your compost is ready to be used. How can you know it’s done? Your compost will appear like a thick, crumbly soil that has the smell of natural earth. At this point, you know your compost is ready to be combined with your topsoil.

What is the Best Ratio of Compost to Soil?

At this point, you have likely decided whether or not you are going to buy premade compost or invest your time and energy into making your own. Whatever you come up with, you need to make sure you are using the right amount in your raised garden bed.

So, how much compost should you add to a raised garden bed? There is actually a specific calculation you should follow when tossing compost in with your soil. The right percentages look like this:

  • 60% high-quality topsoil.
  • 30% compost, either store-bought or homemade.
  • 10% growing mix that is void of any soil, which is also referred to as potting mix.

Keep in mind that there will not be an equal percentage for each of these elements. For instance, if your calculation comes out to be .444 cubic yards of topsoil, you can go ahead and round up to half a yard to make things easier on you.

There is also the issue of the availability of quality topsoil. Some areas do not offer quality topsoil for gardens. In a situation such as this, you will want to change your percentages to the following:

  • 50% of a growing medium that does not include soil, such as potting mix.
  • 50% compost.

The reasoning behind this is simple: if you don’t have access to topsoil that has any type of nutrient density than the compost will need to compensate. For this type of soil situation, the compost will be the main source of nutrients for the plants.

If you include peat moss in your raised garden, it should never exceed more than 20% of the overall mix. This is due to the fact that peat moss has a very high acid level which can wreak havoc on a number of different plants, especially vegetables. It’s best to use a small amount of peat moss, it wanted, or avoid it altogether and opt for potting mix.

If you are looking for an easy-to-use calculator that will show you the exact measurements needed in your raised garden bed, visit this website. With a few simple questions including garden style, shape, and measurements, you will be given exact percentages of topsoil, growing mediums, and compost to use.

Can You Use Too Much Compost?

With all of this talk about how wonderful compost is for plants, it may come to mind that using compost in place of soil is a good idea. It makes sense, right? Soil made completely of compost will be sprawling with nutrients and beneficial bacteria and fungi, so why not use it instead of a blend with seemingly useless topsoil and potting soil?

It may come as a surprise but using too much compost can cause more harm than good. That is why it is always best to stick to a ratio of 60% topsoil and 30% compost when using high-quality topsoil. The potting soil is essentially there to help the garden breathe and drain properly.

At this point, you’re probably wondering: “Why?” Well, a common phrase comes to mind: too much of something is never a good thing, and this is true for compost as well. With an excessive amount of nutrients, plants will grow entirely too fast and won’t have a chance to grow their own pesticides to fend off diseases and pests.

As you can imagine, a plant that is overrun by disease and pests with no adequate time to grow will likely perish. That’s why you should never use too much compost in your raised garden bed. A healthy raised garden will be just fine with 30% to 50% of compost embedded in the soil, depending on the quality and type of topsoil you are using.

When to Add Compost to Your Raised Garden Bed

Timing is also a factor when adding compost to your raised garden bed. After all, adding compost mid-season won’t actually benefit your garden all too much as the plants have likely already grown and won’t be able to suck up nutrients from the compost.

So, when is the right time to add compost to your garden? Generally, adding compost to your raised garden bed is best done at the beginning of the season in spring. This will allow your plants to grow with the compost in place, thus paving the way for a stronger, healthier, and overall thriving garden all spring and summer long.

However, if you are using compost with manure you need to place the compost in the fall/winter before you start gardening again in the spring. This is due to the fact that compost that contains manure needs extra time to decompose. This type of manure will benefit greatly from the frosting and thawing that the colder months bring. By the time spring rolls around, it should be ready to go.

How Much Compost Should Be Added to a Raised Garden Bed?

Knowing the proper ratio of topsoil to compost is only half the battle. The compost needs to be tilled into the soil. Unlike mulch, which sits on top of the soil and seeps in over time, compost works differently. It needs to be placed in the topsoil in order to work. But how much and how deep should the compost actually go?

A basic rule of thumb when it comes to how deep and how much compost should be added is this:

  • A garden with limited organic matter, such as a raised garden bed that does not have quality topsoil, should have 4 to 6 inches of compost. The compost should be placed before planting season, so it’s ready to help the plants grow and thrive.
  • On the other hand, a garden that has plenty of organic matter and high-quality topsoil won’t need to worry as much. Organically rich topsoil should have around 1 to 3 inches of compost placed in the topsoil before each planting season begins.

Remember that any time you add compost to your soil, you don’t need to expel too much energy for mixing. Over-mixing can actually cause problems for your soil. Instead, give the compost a light tilling through the top of the soil.

If you are interested in seeing how to properly add compost into a raised garden bed, you can see an excellent video here.


Every garden needs compost and that includes the beloved raised garden bed. Just remember that nutrient-dense topsoil only needs around 30% of compost placed in the top 1 to 3 inches of the soil. Soil that lacks nutrients may require up to 50% of compost that can be placed in the top 4 to 6 inches.  

Eyerly Family

The Eyerly Family is a family of 8 that loves gardening. Over the past several years we have been applying what we learn about gardening to our own 16x16 raised back yard garden. Our garden is very prolific and we grow a wide variety of vegetables which we love to eat! Click here to learn more about the Eyerly Family.

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