Use this guide to learn the best soil for raised garden beds, how much soil you need to fill your garden bed, how often to mix in more soil, and more!
The Importance of Good Soil
After you test your soil, you will find that adding compost can usually correct nutrient deficiencies. Soil rich in organic matter is dark, and chock-full of nutrients plants need to grow.
The healthier the soil, the more nutrients the plant contains, so it provides us with more nutrients as we harvest our vegetables.
Adding compost to native soil helps add decomposing materials to the soil and helps the soil retain moisture. That’s why we practice large-scale composting from our barn waste and vermicomposting to create a worm-casting compost from our kitchen waste.
Rich soil also makes a perfect habitat for worms and other helpful insects. The worm castings act as an organic fertilizer, and the worms keep the soil aerated and loose. You want to avoid hard, compacted soil in your garden. Plant roots thrive in loose, aerated soil.
So, as you and your kids find worms in your compost or garden, keep them there to breed and multiply. The presence of worms is one sign of healthy soil.
How Much Soil Is Needed for a Raised Garden Bed
Fill your raised garden beds with more soil than you think it needs. The rain, heat from the sun, watering and other factors will compact the soil over time. Fill your beds until the soil reaches one or two inches from the top of the garden bed frame.
You can calculate how much soil you will need for your raised beds by multiplying the length by height by the width of your raised bed in feet. This formula will give you the volume or the amount of soil you need in cubic feet.
For example, if your garden bed measures 4 feet by 8 feet by 10 inches, you will need 26.6 cubic feet of soil.
Buy more garden soil than you calculate. If you figure 26.6 cubic feet of soil, buy 32 cubic feet. You want to be able to fill your raised beds fully, and most gardeners will find that they don’t ever have too much soil.
Pro-Tip: If you have deep raised beds, fill the bottom with decomposing logs or branches (known as the Hugelkulture method). The logs will break down over time, adding more nutrients to your soil. Or, line the bottom with medium-sized rocks to take up space and provide excellent drainage.
How Often Should Fresh Soil Be Added
You should plan to add compost to your soil for raised beds every year. Lightly mix in the compost with the existing garden bed soil, but don’t stir things up too much, all this does is bring those weed seeds to the surface.
Adding compost introduces new organic matter that will feed your plants. Before planting, test your soil to check the pH and essential nutrients. That way, you can intentionally amend it if needed.
What Is the Best Soil for Raised Garden Beds
The best soil for raised garden beds is a mixture of native soil, peat moss, and compost. The idea that we can turn kitchen scraps, animal waste, yard waste, and more into rich nutrients for our garden is so satisfying.
Horse manure makes excellent compost too. Minerals that the horses consume get passed into the manure and grains, seeds, hay, grass, and other compostable materials. We don’t have horses on our farm, so we source ours from a local farmer.
Horse manure has to be composted for at least nine months before you use it, so make sure you know how long the compost has been aging and curing. Otherwise, the seeds in the manure will not be broken down, and they will be reseeded as weeds in your garden. No one wants that!
Tips for Filling a Raised Garden Bed
Variety Is Key
Fill your raised bed with compost from a variety of sources. We use a truckload of composted horse manure, compost from our chicken coop and goat barn, and compost from pine mulch, leaves, straw, and more to make a rich blend.
Peat Moss
The addition of peat moss encourages your soil to both retain and shed water as needed. Your raised garden bed soil should consist of about ⅓ of peat moss. Be careful. Too much of a good thing can be a bad thing.
If you overdo it on the peat moss, you can cause your soil to become too acidic. You can easily monitor the pH level of your soil by testing your soil. We love this soil test kit from Redmond, and you can use our code .
Save Your Back
Use a wheelbarrow, truck bed, or our favorite tool, a Gorilla Dump Cart, to transfer the compost to your garden beds. Gorilla Dump Carts have pneumatic tires, a dump bed, and a handle that comes off so you can attach it to your lawn mower.
They come in various sizes, so if you purchase a Gorilla cart, make sure it can fit through the gate into your garden and between your garden rows.
Many Hands Make Light Work
Use shovels to transfer the compost to the cart or wheelbarrow and wheel them to your garden bed. If you have enough shovels for the whole family, everyone can help!
Filling an Existing Bed
Prepare your garden beds for the compost. If you are starting new beds, then begin filling. If you are adding compost to existing beds, disconnect and remove drip lines, debris, garden stakes or anything else you don’t want in the way.
Pro-Tip: If you use drip lines for watering or drip irrigation, blow out your irrigation lines before winter to get all the water out to discourage freezing or breaking of your irrigation lines.
Fill your garden beds with the compost or mix it into the existing soil underneath. Level the compost as you mix it in. Fill the beds until the soil reaches about two inches from the top of the garden bed frame.
Reattach or add your drip irrigation lines to the beds (check out our full tutorial for setting up an automatic drip irrigation system). Make sure the lines run lengthwise down your garden bed, spread them out evenly, and stake them down.
And that’s it! With this easy plan, you should be able to grow food every year, provide enough nutrition for your plants, and have a flourishing garden.
