How Much Soil Do I Need For a Raised Garden Bed? (Formula + Save Soil Costs)

You've heard about raised beds, but where does the soil come from? When building a raised bed for the first time, it's not always easy to determine how much soil you'll need. This article will lead you step-by-step through determining how much soil you should use in your raised garden bed.

Raised beds are not just great for gardening. They're also a way of saving space in your yard. You can use raised beds the same way as traditional gardening beds with soil, but they are elevated and therefore more efficient. This article will show you how to calculate how much soil you need for a raised garden bed and how to obtain composted manure (compost) for your soil.

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Table Of Contents

How to Calculate the Volume of Soil Needed For Raised Garden Beds

You can calculate the amount of soil needed for raised garden beds. The most accurate way is to dig out a yard section and measure the area. However, you can use the following formulas according to the shape of your raised bed.

Things you will need to calculate soil:

• Tape
• Pencil and paper or calculator
• Soil test kit

Once you have all these items ready, look at your garden bed dimensions.

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Formula for rectangular raised bed soil volume

The soil volume needed for a raised garden bed depends on the soil you use, how deep you dig and whether you have existing soil.

The formula for calculating the volume of soil needed for a rectangular raised bed is:

V = L x W x H

Where:

V = Volume in cubic feet (ft3)

L = Length in feet (ft) W = Width in feet (ft)

H = Height in feet (ft)

Measure the length, width, and height of your finished raised bed. It will give you three numbers that you can use to calculate how much soil you need for your raised bed.

Multiply your measurements and convert the answer into cubic yards by dividing it by 27. The answer you get after converting is the amount of soil needed to cover your entire rectangular garden bed.

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Formula for circular raised beds

The soil volume in circular raised beds is based on the diameter of the bed. The formula for calculating this is:

Volume = r^2 x 3.14 x H

Where:

Volume = Volume of soil in cubic feet (ft3)

r = Radius of your circle (ft)

H = Height of your circle (ft)

Find the radius by dividing the circle's diameter by two, then square it. Multiply the squared radius with 3.14, then multiply with the height to find the required volume.

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Amount of Soil Depth for Raised Beds

The soil you need depends on the plant you want to grow, how high your bed isd the soil type in your garden area.

If you have a raised bed and want to grow 12-18 inch deep-rooted plants, then you need at least 6-8 cubic feet of well-drained soil. For shallow rooted plants such as tomatoes or peppers, you will need at least 4 cubic feet. If you have a raised bed 24-36 inches high, you will need at least 10 cubic feet of good-quality soil. Deep-rooted plants require deeper soil than shallow-rooted plants.

Shallow rooted 12'-18' plants are:

• Large leaf vegetables include cabbage, broccoli, kale and collard greens.
• Tomatoes, peppers and eggplant.
• Herbs: basil, oregano and thyme.

Deep-rooted 24'-36' plants are:

• Lettuce
• Cucumbers
• Peppers
• Carrots
• Radishes

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The Right Mixture of Soil for Raised Beds

The best mix of materials will depend on the type of plant you want to grow in your raised bed. The right soil mixture for raised beds is 60% quality soil, 30% compost, and 10% add-ins. The compost or other organic materials can be peat moss or sphagnum moss to the top 6 inches of the bed mix before tamping down the soil. Some add-ins include manure, leaf mold or peat moss.

The ratio of 60/40 will ensure that your soil holds nutrients well and has the right balance of minerals and organic matter.

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How to Save Soil Costs for Raised Bed?

Raised Bed require more soil than other gardening methods, and the soil can get expensive.

The hugelkultur method is the easiest and most cost-efficient method to save costs.

Hugelkultur is the process of layering organic garden waste inside the raised garden bed, before adding soil to save on costs, in addition to attracting and preserving moisture. Of German origin, hugelkultur translates to “hill culture.”

The materials used in Anaerobic Composting can be made up of rotting logs, sticks, and other debris mixed with things like coffee grounds and grass clippings.When materials break down, they provide a healthy environment for fungi and microbes. Hugelkultur is advantageous in that it improves soil quality, requires minimal maintenance, and retains water well. 

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More specific questions about Soil Do You Need For a Raised Garden Bed

How many inches of soil do I need for a raised garden bed?

A raised bed does not need to be very deep to be effective. 8 to 12 inches is usually adequate. If drainage is a problem, or if the plants you are growing prefer drier soil, the bed could be taller and filled with a porous growing medium. Vegetable beds should be 12 to 18 inches deep. Learn more about how deep a raised garden bed needs.

How many cubic feet are in a 40-pound bag of soil?

A 40lb bag of dirt mixed with topsoil yields 0.75 cubic feet, and 1 cubic yard is equal to 27 cubic feet, so there are 36 bags of 40lb of topsoil in a cubic yard.

How many bags of soil do I need for a 2x4-foot raised bed?

For a 4x4 raised garden bed, you will need 7 bags of soil (1.5 cubic feet per bag) or 10.72 cubic feet of soil. This is assuming your raised garden bed is 8 inches high and the bags of soil you are buying contain 1.5 cubic feet of soil per bag.

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Conclusion

This article reviewed the most important factors that influence the amount of soil needed for a raised garden bed. Keeping these in mind will enable you to calculate the exact quantity of soil you need for your project. However, if you are still unsure about how much soil is required for a raised garden bed, you can purchase it.

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