One of the most popular questions I see from new gardeners is how to fill a new raised bed with soil. Many different methods are out there that work great! Everyone has different opinions and different materials available. I have researched a great deal to find how others have filled raised beds.
Here are the four best ways to fill a raised garden.
- Core Gardening
- Ruth Stout
- Back to Eden
Before we get started, if your raised bed has not been built yet, it may be good to take a look at our article Are Raised Garden Beds Better Than In-Ground Garden Beds?. This may help you decide which is the best option for your soil and climate.
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Let’s get into the details of the best ways to fill a raised garden bed!
Calculate the Amount of Soil Needed
Before we get to the list, I think it is important to understand how much soil and organic material might be needed in order to fill a raised bed. Whether buying bags of material or buying in bulk by the yard, a little math is necessary to get a good estimate for how much is needed and what that might cost.
First, calculate the volume of the raised bed. This tells how much material the bed can hold.
Volume (cubic feet) = Length (feet) x Width (feet) x Height (feet)
Using a tape measure, measure the longest side of the bed, which is the length. Then, measure the shorter side, which is the width. Finally, measure the depth/height of the bed. If all of these measurements are in feet, the final volume answer will be in cubic feet.
For the sake of this article, let’s use an example of a raised garden bed that is four feet wide by eight feet long by one foot high. This is a pretty standard size garden bed. Our volume calculation would then be:
32 cubic feet = 8 L x 4 W x 1 H
It is normal to see bags of soil and compost in bags that are two cubic feet at garden stores. So thirty-two divided by two would mean that sixteen bags of material are necessary to fill this raised bed.
If the garden being filled is a large raised bed or multiple raised beds, it is probably a better deal to buy in bulk and get the material in cubic yards. In this case, divide the volume in cubic feet by twenty-seven in order to find out how many cubic yards of material is necessary. In our example, 32 divided by 27 equals about 1.18 cubic yards. So you would just buy 1 cubic yard of material.
I will reference some of these examples and methods for calculating the amount of material needed for a raised bed in the methods below.
1. Core Gardening
The concept of core gardening is to create an internal “sponge” down the middle of the garden bed. This core holds water like a sponge and will be able to wick moisture two feet in both directions.
Here are some of the benefits of the core gardening method:
- Less watering! Due to the core being able to hold water all season long, the garden will need to be watered much less (if at all depending on the climate). If mulch is kept on top of the soil, this will help with less watering even more!
- Fewer weeds! The surface of the soil can stay dry if the garden does not need watering very often. This means weed seeds have less of a chance of sprouting because they need water in order to germinate. Again, if the soil is kept mulched (as I ALWAYS recommend), weeds will most likely be smothered if they do happen to be able to sprout. This is just another benefit of covering gardens with mulch!
- Stronger root system for plants. Since the surface of the soil is dry, the roots of the plants will reach farther down into the soil for water provided by the core. This also helps the plants reach nutrients that are deeper into the soil and helps create a more healthy and strong plant.
- Reduces disease issues. Many disease issues are caused by too much moisture at the surface of the soil. By having the moisture for the plants be controlled by the core, the chances for fungus, mold, blight, and powdery mildew issues are greatly reduced.
Steps to create a core gardening raised bed.
These steps can be used whether you have an existing raised bed or you are filling up a new empty raised bed.
Build a trench for the core
Build a trench around 8-12 inches deep and about 1-2 feet down the middle of the raised bed. If an existing raised bed is being utilized, just push the soil to the sides or temporarily remove the soil.
For a new raised bed, first, I recommend putting cardboard or newspaper down for the base of the bed, assuming it is right on the ground. This will smother any grass or weeds that might exist. It is not even necessary to remove these weeds or grass first. Put some of the soil of choice (discussed later) on top of the cardboard/newspaper, but only a small amount depending on the height of the bed. Then, start the trench as mentioned above.
Fill the core of the raised bed
The core of the raised bed should be filled with wet organic matter that has already started to break down. The best and most recommended material to use is old straw bales. These can undoubtedly be found for free after Halloween! Just let them sit outside all winter to start breaking down before adding them to the core.
Other material that can be used in conjunction or in place of straw is old twigs, leaves or grass clippings. These items can be mixed together if they are all available. Either way, the core should be free to fill!
Fill up the core/trench with organic matter. Walk on top of the material to pack it down really well. I recommend shooting for about 4-5 inches thick of packed down material. It will be perfectly fine to have a slight mound down the center of the bed when it is finished because this will settle over time.
Charge the core!
Make sure to water the core thoroughly. This is referred to as “charging the core”. The whole purpose of the core gardening method is to create a sponge down the center of the bed that provides water to the plants all season long. Do not skip the step of watering the core!
Fill in the rest of the raised bed with soil
If an existing raised bed was being utilized, just fill back in the soil that was temporarily removed to create the trench for the core. Again, it is perfectly fine to have a slight mound down the middle. It will settle over time.
If a new raised bed is being filled, then decide on soil type and how much will be needed. Do not get really fancy with this. A 50/50 mixture of garden/topsoil and compost will do just fine for a raised bed.
Let’s use our example raised bed from above of 8 feet by 4 feet by 1 foot high. We said this was a total of 32 cubic feet. We have to estimate how much space our core might be using up because we can subtract this volume from how much soil we will need to fill in.
If our core is 2 feet wide by 8 feet long by 5 inches high, multiplying these numbers together (height converted to feet is 5 divided by 12 which equals .42) equals 6.6 cubic feet. I would recommend rounding this number down, causing you to get slightly more soil than you think you might need since the soil will settle over time.
So we had a total of 32 cubic feet of space in our raised bed and we filled up 6 cubic feet with soil, so we need 26 cubic feet of soil left to fill.
You can buy 7 bags of organic garden/topsoil and 7 bags of compost where each bag is 2 cubic feet in volume (so you would have 28 cubic feet). Depending on prices per area, this could reach a total of about $100. This may be too expensive for some gardeners.
It is possible to get this price down even cheaper! Try to find someone that has topsoil available for free, perhaps from a recent construction project. I also recommend working on making homemade compost to help reduce the cost, but this would obviously take time to produce.
Perhaps the best option is to buy the soil components in bulk. Topsoil and compost can be purchased by the yard. One yard is equal to twenty-seven cubic feet. In our example, we needed twenty-six cubic feet. The store may or may not sell topsoil and compost in half yards. If they only sell it by the yard, it will still more than likely be a less total cost than buying a half yard of bagged material, so essentially, two raised beds could be built for the price of one!
Supply some additional nutrients and plant!
Most likely, a new raised bed will need to be supplied with some additional nutrients. It would be good to find an organic granular fertilizer and perhaps a good nitrogen source such as manure or fish fertilizer. Keep your bed mulched at all times and add compost to the top of the soil every year and the need to purchase organic fertilizers should be eliminated in the future!
What should be done the next season?
After a year has passed, the core is most likely going to be gone. The organic material will have turned into great compost for the garden and the worms will be naturally tilling the garden.
Many people like to recreate the core year after year. Gardeners who build a trench again, fill in the organic matter, and charge the core are good to go for another year.
This probably works perfectly fine, and no doubt it is a better method than tilling the garden. However, I cannot get past the fact that the soil is being disturbed every year. Plus, it is extra work!
After the first or maybe the second year of implementing the core gardening method, I do not feel it is necessary to keep recreating it unless the garden happens to be in a very dry climate or the gardener just has no time to water, even infrequently.
If the soil is kept covered with mulch at all times and compost is added to the top of the soil each year, then healthy soil is definitely being built and the critical soil life below is not being disturbed. I feel it is not necessary for the extra work of creating a core each year in most cases.
2. Hugelkultur Raised Bed
Hugelkultur is the process of burying large amounts of rotting debris under the soil. This usually includes large rotting logs, sticks and other debris.
As you may have noticed, the Hugelkultur method is very similar to the core gardening method. The benefits are almost identical, so I will not repeat them here in full detail.
A large sponge is still being created under the soil that holds water well and gives the plants nutrients. The roots of the plants will travel deeper into the soil to obtain the nutrients and water, which creates stronger plants.
One difference with this method is that the material underneath is much larger and will take a lot longer to decompose. This means it could last up to five years before that base sponge has turned into wonderful soil. While the material breaks down, it will heat up and create a microclimate under the plants and warm the soil, which can be useful in a colder climate.
Steps to create a Hugelkultur bed
The goal is to place rotting wood and other debris about 10-12 inches deep in the bed. If an existing raised bed is being used, dig out all the soil first. It may even be necessary to dig down deeper than ground level to get to this depth. Set the soil aside for now.
For a new raised bed, it is possible to save money later by digging into the existing topsoil and setting this aside. For our raised bed example above which is twelve inches deep, you may want to dig three to four inches of topsoil out. This will be three to four inches of soil you will not have to purchase later!
Now find old rotting logs, twigs, and other debris and throw them into the bottom of the raised bed. It is important that wood that is already starting to rot is being used, as this will hold water and provide nutrients to the plants much better than fresh wood.
Fill in all the extra space and gaps between the large logs with leaves, grass clippings, trimmings from bushes, wood chips, etc. This takes up space with free materials so it’s not necessary to spend as much money on filling up the bed.
Water all the organic material
Next make sure all the logs, leaves, grass clippings, and the like are well watered, similar to the core gardening method above. This material will be the source of water for the plants above it all season long.
Fill in the rest of your raised bed with soil
Ideally, a good amount of existing topsoil would have been dug out at the beginning of this process, so it may not be necessary to purchase much more. It may be a good idea to mix this topsoil with some bags of compost if more material is necessary to get your beds to full capacity.
Even if this garden was started with a brand new raised bed and three to four inches of topsoil was dug out, I don’t believe any additional soil will be necessary. If all of this topsoil is placed back on top of the rotting material, and then a few inches of mulch is added on top of the soil, this project should be virtually free!
Timing and final thoughts
This method may or not be right in any given situation depending on access to rotting logs and other material. But if these resources are available, then this can definitely be a free way to start a new garden bed or enhance an existing one!
This method can be constructed in the spring and the garden can be planted right away, or it can be started in the fall to allow the organic matter to break down all winter long and then the garden can be planted the following spring. The buried debris will feed the soil for about five years.
Again, it may be beneficial to use some organic fertilizer, manure, or fish fertilizer in the first year to jump-start the feeding of the soil in a new raised bed. However, if you follow our principles of adding compost to the top of the soil each year and keeping the soil mulched at all times, your need to purchase fertilizers in the future should be eliminated! No one fertilizes the soil in nature and everything grows just fine!
3. Ruth Stout Garden Bed
Ruth Stout was a woman who was born in the United States in 1884 and nicknamed the “Mulch Queen”. She originally started gardening by tilling the ground every year, killing the soil life, and creating much more work for herself than there needed to be. Eventually, she discovered the power of mulch, particularly spoiled hay.
The Ruth Stout method promotes the use of mulching the garden with spoiled hay and building healthy soil quickly. Hay breaks down quickly, feeds the soil and reduces watering.
Now, keep in mind: hay tends to have an abundance of weed seeds! However, this method requires a thick layer of at least eight inches of hay at all times, and most weeds cannot germinate through this thick layer of mulch.
Starting a Ruth Stout garden bed is great to do in the fall in preparation for spring planting. However, if it is spring time, a Ruth Stout bed is a great way to start potatoes right away!
Steps to create a Ruth Stout garden bed
This method is probably the easiest to implement and the cost is very minimal assuming access to free hay.
A Ruth Stout garden bed should be built directly on the ground, but it is not required to have sides. However, I feel like having a standard garden bed with sides is a good idea just to keep everything contained – especially in windy areas.
Start by adding a few inches of compost/aged manure right on top of the ground. It is not necessary to kill or remove any grass or weeds! Buy these products in bags as we discussed above or buy in bulk to save money. Any extra compost or manure can be saved to be used in another garden or used at a later time to add nutrients to this garden bed.
At this point, it is the perfect time to plant potatoes throughout this whole bed in the Spring! Do some research and buy seed potatoes that are suitable for your specific area. Do not cut the seed potatoes before planting. Just put the entire whole seed potato about halfway into the layer of compost/manure. If the potato is still visible on the surface, that is perfectly fine.
Now, spread the spoiled hay throughout the bed on top of the potatoes. The hay should be spread evenly and be eight to twelve inches deep. That is really all it takes to get this bed started! It is not necessary to water or touch this bed and a great potato harvest will occur!
This is a great method for getting a garden bed started for little to no money. It helps build soil fast, and in future seasons potatoes can be planted in the same way and more hay can be added, or other crops can be planted in the soil that has been built.
When planting other crops, the hay must be pushed to the side and the seeds/transplants be planted into the soil. As the plants grow, the hay can be pushed back around the plants as mulch.
This same concept for starting potatoes can be done with wood chips if hay is not easily accessible. We will talk more about wood chips in the next method!
4. Back to Eden Garden Bed
In your gardening research, you may have come across the term Back to Eden gardening. This approach has been made famous by Paul Gautschi. I highly recommend watching his film and videos on YouTube which you can find by simply searching for “Back to Eden Paul Gautschi”.
Paul did not invent or discover anything that didn’t already exist. Like Ruth Stout, after years of hard labor in the garden by tilling the ground, he discovered the power of covering the soil with mulch and mimicking nature and God’s design. Unlike Ruth Stout, he found great success with using free wood chips as his mulch of choice along with composted chicken manure.
The benefits of a Back to Eden garden are very similar to the other methods discussed above and these gardens can be started for very little cost. The wood chips help build healthy soil as they break down, provide nutrients to plants, reduce weeds, and hold the correct amount of moisture that plants need.
Steps to create a Back to Eden garden
Again, this method can be done with or without a raised garden frame. It is mostly recommended to start out a new bed by covering the ground with cardboard or newspaper. Wet this down so it smothers out all the grass and weeds.
Next, get some soil. Similar to the above methods, a 50/50 ratio of compost/aged manure and topsoil can be mixed and used. This might be available for free or it can be purchased by the bag or in bulk by the yard. A raised bed should be filled about halfway, or about six inches. To save some money, first, implement a subset of one of the first two methods above by putting some organic matter on top of the cardboard/newspaper.
On top of the soil is where the wood chips should be as the mulch layer. The wood chips can be as deep as desired, but generally about four inches or so would work well with the above method.
Wood chips should be able to be obtained for free by calling around to local landscaping and tree companies. They often get charged for dumping their wood chips at designated locations and would be more than happy to give their wood chips away for free. For those who are picky, wood chips created from a wood chipper are better than wood chips created from a wood shredder (both work fine!). A chipper will chop up the wood chips in a way that creates more surface area and will help the material break down faster. The way it lays together will also help prevent a suitable environment for slugs.
To save money, put wood chips right on top of the grass and weeds and don’t buy any extra soil. In this case, make sure the wood chips are piled at least eight inches deep.
In either case, do not ever mix the wood chips in with the soil. Also, never plant seeds or transplants in the wood chips. As with any mulch, always make sure to push back the wood chips and plant in the soil. The first few seasons, some organic fertilizer may need to be added, but over time, the wood chips will break down and create healthy and fertile soil for plants.
So that’s it! Those are four easy ways to start or enhance a raised garden bed. It all depends on which resources are available for free. Do not be afraid to ask around for these resources. Some cities have a free mulch and compost program. Farmers are also a great option for manure, straw, and hay. Wood chips and leaves should be the easiest resource to find from landscaping and tree companies or just on the side of the road from homes in the Fall.
This might be obvious, but each method is essentially the same thing – building soil with natural organic matter and always covering the soil with mulch. This is exactly how nature works! We just like to speed up the process a bit for our own gardening needs.
For he was looking forward to the city with foundations, whose architect and builder is God.Hebrews 11:10
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