How to Fill Raised Garden Beds

If you have empty raised garden beds it can feel overwhelming to fill them up. In this post, I will give you tips and techniques on how to easily fill your raised garden beds with the right soil mixture so that you can save money and start off with a healthy and productive garden.

Raised garden bed filled with soil

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Raised garden beds are a popular choice for growing vegetables, herbs, and flowers. They make planting and harvesting easier. They keep your plants contained to a specific area. Plus they are an easy option if you’re starting your garden for the first time.

But before you start planting, it’s important to know how to properly fill your raised garden beds so that you can start off with a healthy garden.

So let’s get to it!

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Choose the Correct Raised Bed

Before filling your raised beds it’s important that your raised beds are a size worth planting in. Ideally raised beds should be at least 12 inches deep and placed on a surface that roots can grow into.

For example, I have raised beds that are built on top of dirt that are only about 10 inches deep but everything grows great because plant roots can grow into the ground below the raised beds.

But if the plants can’t grow into the surface below the raised bed I’d recommend a height of 17-24 inches and that should be good for most vegetables, herbs, and flowers.

The length of your raised bed doesn’t matter quite as much, but a width of 3-4 feet is perfect because then you can reach into the center of your bed. Any wider and you’ll have to get inside your raised bed for planting and harvesting.

What to Add to the Bottom of Raised Beds?

The short answer is nothing.

Raised beds filled entirely with a good mix of soil is your best option.

It’s very common to see gardeners filling the bottom of their raised beds with sticks, logs, leaves, and all sorts of organic matter to fill up some of the space. It’s an idea taken from a gardening technique called hugelkultur.

However it’s not a method I recommend. I tested it out for a year in my Olle Gardens raised beds and had very poor results.

The problem with this method is that it reduces the amount of soil available for plant roots to grow in. The next problem is that organic materials decompose and so in time the soil level is going to drop and you will need to add more soil anyways. It’s better to just add all soil right from the start.

The other problem with wood in the bottom of the raised beds is that the microbes that help with the decomposition process require nitrogen which means they’ll be stealing the nitrogen from the soil around the wood, reducing the amount available for your plants.

Choose the Right Soil Mix

The perfect mixture to fill your raised beds is 70-75% topsoil plus 25-30% compost. You can mix this together and fill the raised bed completely.

Topsoil consists of the top few inches of soil. You may have access to topsoil on your own property or it can be purchased in bulk which is a much more cost effective option than purchasing individual bags.

Topsoil is made up of sand, silt, and clay and holds onto moisture, plus doesn’t break down like soilless mixtures do. However, in some areas topsoil can be heavy in clay or sand.

If that’s the case, consider ordering in bulk elsewhere or using a triple mix which contains 1/3 topsoil, 1/3 compost, and 1/3 peat moss.

But keep in mind that this mixture is a majority organic matter and is going to decompose. In time soil levels are going to drop and you’ll have to keep topping of your garden beds.

So the best scenario if possible, is filling your beds with 70-75% topsoil plus 25-30% compost.

I know this goes against common gardening advice out there with gardeners teaching about making the “perfect” soil but the perfect garden soil is what exists in nature.

Before housing developments were built the land was a field or forest that grew plants. In commercial agriculture, crops are grown in real soil.

Formula for Calculating How Much Soil to Get

As you prepare to fill up your garden beds, keep in mind that soil in bulk is typically measured in yards.

Here is the formula you will need to convert the size of your raised beds into cubic yards to help you calculate how much soil to get.

Formula for cubic yards,

Length (ft) x Width (ft) x Depth (ft) / 27 = yards of soil

  • 27 cubic feet = 1 yard of soil

Formula for cubic feet,

Length (ft) x Width (ft) x Depth (ft) = cubic feet of soil

  • Example: 8′ (Length) x 3′ (Width) x 1′ (Depth) = 24 cubic feet of soil

The important thing to remember is that each measurement has to be measured in feet, not inches. For example, if the depth is 15 inches, you need to divide 15 by 12 which is 1.25 feet.

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Add Compost for Nutrients

Adding compost to your raised garden bed is a great way to provide your plants with the nutrients they need to thrive. Compost is rich in organic matter, which helps to improve soil structure and fertility.

You can make your own compost by collecting kitchen scraps, yard waste, and other organic materials and allowing them to decompose over time.

Or, you can purchase compost or soil amendments from a garden center or nursery.

When you initially fill your raised beds you can use around 25-30% compost mixed with your topsoil. But then at the end of each season you only need to spread a 2 inch layer on top of your soil.

Use Mulch to Retain Moisture

Mulching your raised garden bed is an effective way to retain moisture and suppress weed growth. Organic mulches like straw, leaves, and wood chips are great options.

Apply a layer of mulch about 3-4 inches deep around your plants, being careful not to cover the stems or leaves. This will help keep the soil moist and reduce the need for frequent watering.

Are you looking for raised garden beds for your own garden?

  • I really love the raised beds that Olle Gardens offers.
  • You can use the code AUDREY10 at checkout and save 10%.

Are you ready to start a raised bed garden?

If so, be sure to check out my masterclass, How to Start and Grow a Raised Bed Garden.

This masterclass will give you actionable tips and advice whether you are just a beginner gardener or consider yourself a pro!

Cover image of my masterclass, How to Start and Grow a Raised Bed Garden

What You’ll Learn…

  • The pros and cons of raised bed gardening and how to decide if it’s a right fit for you and your gardening goals.
  • Where to put your raised beds and a walkthrough of different raised bed options whether you are wanting to buy them or build them yourself. 
  • How to choose the best plants to put in your raised beds, a list of varieties better suited for smaller spaces, and the difference between different plant varieties that take up less space. 
  • How to maximize your space with companion planting and succession planting strategies. As well as how to implement vertical growing when possible. 
  • How to fill raised garden beds and a formula that will help you figure out the correct amount of soil to get in both yards and cubic feet.

Get your free Vegetable Planting Schedule!

Sign up and get this planting schedule with all planting dates sent straight to your inbox!!

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