Many newly built wood raised beds that are freshly filled with soil.

Compost & Soil Health, Garden, Getting Started, Raised Garden Beds

How to Fill Raised Garden Beds with Organic Soil

March 22, 2019 /

Last Updated on February 28, 2025

Do you have new planter boxes that need filling? Read along and learn how to fill raised garden beds with quality organic soil that is well-balanced, nutrient-rich, and microbially-active to help your plants thrive. After all, soil health is KEY to the overall health and productivity of your garden! It’s something you want to “get right” from the start.

In this article I will share our raised bed soil recipe – with options for using bagged or bulk soil, compost, and our favorite organic fertilizers or other amendments. Learn how to calculate bed volume and soil needs, the importance of mulch, and explore the hugelkultur method to fill raised garden beds. Last but not least, I’ve included tips on how to improve existing soil if your garden beds are already full but underperforming.

Aaron stands next to a raised bed with a shovel, a Kubota UTV is backed up to the bed with its bed fully inverted to dump the bulk soil into the bed. — Filling the raised beds in our newer garden space – with the assistance of a UTV since we had 19 beds to fill! Most of the other photos you’ll see throughout this post are from our old garden, where we did everything by shovel and wheelbarrow.

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Getting Started with Raised Beds

Don’t miss our guide on how to build a durable DIY raised garden bed! The tutorial includes a step-by-step video and explores wood choices, bed sizing, location and layout best practices, tips for gopher-proofing beds, non-toxic sealer, and other ways to make wood raised beds last longer.

Don’t want to build your own? Check out the high-quality, long-lasting, galvanized metal Birdies raised beds from Epic Gardening – code “deannacat3” will save 5%! We love our Birdies too.

Once you have your beds in place, it’s time to fill ’em up.

A garden space in a front yard with a house beyond. A variety of vegetables are growing along with many perennials and agave growing in the ground. — Our old front yard garden

Investing in quality raised bed soil

Let’s set the record straight: “Dirt” is not soil! Soil is rich, full of nutrients, critters, microorganisms, and is biologically active! In contrast, dirt is usually devoid of all these things. Soil improves with time and age, as the soil food web blossoms. It is a living, breathing, dynamic ecosystem of its own.

No matter how much love, energy, or money you invest into your garden, if you have crummy soil, the result will be crummy plants. If you’ve gone through the effort to build or buy yourself some awesome raised garden beds, why skimp on the soil? However, the answer isn’t as simple as “go grab X brand of soil”. In my experience, not one soil is going to be perfect for growing vegetables on its own – bulk or bagged.

If you’re blessed with decent native soil, you can use some of that to fill your raised beds to offset cost (explored below).

A diagram by Heidelberg Farms showing what the Soil Food Web looks like below ground. There are tree roots with compost and micro arthropods on the soil surface, with bacteria and fungi, mycorrhizae, and nematodes and protozoa below the soil surface, in and around the tree roots. — The Soil Food Web. Image Courtesy of Heidelberg Farms via Pinterest

The Best Soil for Raised Beds

Confined to a large container, raised bed soil needs are unique and slightly different than in-ground gardens. The goal is to fill raised beds with soil that’s fertile, rich in organic matter, holds moisture, but also has good drainage and plenty of air pockets using a combination of quality organic soil (bagged and/or bulk), compost, and an aeration additive.

Our raised bed soil recipe

40% soil (topsoil, loam, native soil, etc)
40% well-aged compost
20% aeration (e.g. sand, lava fines, perlite, pumice, coco coir, peat moss, and/or rice hulls)
Other amendments such as worm castings and gentle, slow-release organic fertilizers

We’ll talk about each of these components in more detail below. Note that the ratios are approximate; they don’t need to be exact. Also note that the ratios will change if you primarily use bagged soil, which usually already includes compost and aeration (perlite) – such as 80% bagged potting soil and 20% compost.

Two hands cupping rich brown organic soil with a few red worms, hovering over a garden bed with leafy greens in the background below.

Calculating Soil Volume

Before soil shopping, you’ll need first to calculate the internal volume of your bed(s). Bags of soil come in measurements of cubic feet, usually in a range of 1 to 3 cubic-foot bags. Bulk soil purchased from a local landscape supply company will be in cubic yards.

To calculate how much soil you need to fill a raised garden bed, begin by determining the volume of your bed in cubic feet. To do this, simply multiply the width by length by depth in feet (For example: 4’ x 8’ x 1.5′ = 48 cubic feet).

Now you have your total cubic feet, and can figure out how much bagged soil it would take to fill the bed. If you’re using bulk soil or compost too, you’ll need to calculate volume in cubic yards. To convert to cubic yards, simply multiply cubic feet by 0.037037 (or use this converter). Given the example of a 4×8′ by 1.5-foot deep bed used above, 48 x 0.037037 = 1.7 cubic yards of soil is needed to fill it.

If math isn’t your strong suit (or you’re just feeling lazy…. no shame!) here is a raised bed soil calculator that will do it all for you, in both cubic feet or yards.

a young blonde woman sitting inside a large, deep, empty wooden raised garden bed frame sitting on a concrete patio, just built and not yet filled with soil — A new bed for the old backyard garden

40% SOIL

Using Bulk vs Bagged Soil (or compost)

If you calculated that you need several yards of soil to fill your raised garden beds, you are not going to want to rely on bagged soil alone. The cost will add up quick! Look up local landscape supply companies and see what they offer in bulk – either for delivery or for pick-up, if you have a truck.

On the other hand, if you need to fill only one or two modest raised beds, purchasing bagged soil could be the way to go.

We often get bulk soil and compost delivered from Central Coast Landscaping or Mier Brothers here on the California Central Coast.

Bulk Soil Options

Bulk soil quality, composition and type will vary depending on your location. In our area, we’ve found varying grades of bulk soil including basic topsoil or “fill”, some premium container blends (similar to bagged soil), and a middle-of-the-road “planters mix” that is 2 parts top soil, 1 part compost and 1 part soil conditioner.

The composition of bulk soil will influence how much/what else to mix with it. For instance, if you all you can find is basic fill or topsoil, then you’ll want to follow the full raised bed soil recipe of 40% topsoil, 40% compost and 20% aeration to create a nice well-balanced soil. Or, use mediocre bulk soil as a “filler” at the bottom of deep raised beds, with a better soil on top.

Yet if you’re able to find premium raised bed soil in bulk, then it likely already contains a good amount of compost and aeration (sand, perlite, etc) so you can therefore scale back on those component of the recipe respectively. The landscape supplier should be able to provide details of the ingredients and make-up of the soils they offer!

An image of two very large mounds of soil on a driveway, on top of a blue tarp. It was a delivery of several yards of bulk soil and organic compost. — Years ago, one of the only bulk soil options we had was this “planters mix” (described above) along with a chunky shredded green waste “compost” blend. It honestly wasn’t the best stuff, but helped take up a lot of bulk in the bottom of our beds. We added higher quality bagged materials too.

Deanna standing next to a huge pile of bulk performance blend soil. Beyond is a small pile of lava fines. — In the years since, we’ve found a higher quality bulk “performance blend” soil that we used in our newest raised beds – along with 25% compost and about 5% lava cinders by volume (shown in the background).

Bagged Soil Options

Even if we use good bulk soil to fill the majority of our raised beds, we always add at least a few bags of high-quality organic bagged soil near the top. We’ve used a wide variety of bagged soils over the years, but tend to prefer the selections offered at our local garden centers and nurseries over big box stores. “Hydro” grow shops (those geared towards hemp growers) usually have a great selection of premium soils too.

A few good options include E.B. Stone, Aurora/Roots Organics, Gardener & Bloom (G&B), Dr. Earth’s, and Fox Farms. Other cheaper or generic bagged soil can be used as filler towards the bottom of the bed, especially if you’re filling raised beds with bagged soil alone.

If possible, choose a few different types of bagged soil. Do not use “potting soil” only. It is light, fluffy, and will dry out quickly. In the photo below, you can see that we mix various types of bagged soil and conditioners. By combining a few different things, you’re getting a nice variety of composition and texture. Some are a little more woody, some more fluffy, some with perlite or pumice, some with or without added fertilizers.

A man filling an almost empty wood raised bed with bagged potting soil, holding and dumping in a bag. It is five foot by three feet, and 18 inches deep. Various bagged soils lay around the outside of it, waiting to be added. — For one small raised bed like this, it makes sense to use mostly bagged soil and compost instead of ordering bulk. We mixed several different types/brands of raised bed soil, potting mix, and soil conditioners (plus compost and lava fines).

40% COMPOST

Compost is organic matter that has been thoroughly broken down and decomposed into rich nutrient-dense plant food. It is a phenomenal soil conditioner, boosts the soil food web, and will make your garden shine!

We add plenty of homemade compost from our worm bin, larger compost piles, and aged/composted manure from our mini donkeys, but usually cannot make quite enough to meet all of our needs – especially for large projects like filling new raised garden beds with soil. So we do end up supplementing with organic bagged compost or bulk compost too.

Keep in mind that most bagged soils usually already have compost in them. So unless you’re using plain topsoil in your raised bed soil recipe, feel free to scale the “compost” ratio down to 10-30% (depending on the soil you’re using).

RELATED: See this guide to learn 6 ways to compost at home or this tutorial to learn how to build a DIY compost bin!

Deanna standing in front of one of the bays of a large 3 bay compost bin system. Two of the bays are partially full of donkey manure and leaves.

Compost Options

Many popular soil companies offer bagged compost products too. Again, these can be found at your local garden center or hydroponics grow shops. You should also be able to find compost locally in bulk, which is usually derived from green waste or possibly composted food waste. The bulk compost we purchase is made from local green waste and is OMRI-certified for organic gardening.

Our favorite bagged compost is Malibu Compost Biodynamic Blend. It is made from aged, composted cow manure from certified-organic, biodynamic dairy farms. However, please note that Bu’s compost is quite rich, so they recommend mixing only 25% of their compost to your soil blend.

Unfortunately, Bu’s is primarily available on the West Coast. If you live in the Northeast, Coast of Maine makes a similar product. I’m sure there are many more companies out there, all over the U.S. Leave a comment if you are aware of a good local product like this in your area!

A photo of a bag of compost, by Malibu Compost. It is sitting on the gravel, leaning up against a half-filled raised bed behind it. — We love Bu’s organic compost!

Worm Castings

Last but certainly not least, worm castings (aka worm poop!) are compost too. Worm castings are so good for your plants, they’re referred to as “black gold”. Worm castings offer gentle, slow-release fertilizer as well as improve soil structure, microbe activity, water retention, and drainage.

I highly recommend keeping a worm bin at home! It is a terrific way to divert food waste from the landfill, and up-cycle that “waste” into an incredibly valuable product for your garden or house plants. Worm bins are inexpensive and easy to maintain. Learn how to make a DIY worm bin here!

If you aren’t up for keeping your own worm bin, you could purchase finished worm castings and add at least a small mount to each bed. We can usually find bags of G&B Organics Worm Gro locally, or you could pick up some worm castings online here or from Uncle Jim’s Worm Farm.

A hand holding a handful of rich looking soil, which is actually worm castings. A few red worms are in with the worm castings. In the background, there is a whole tub of worm castings, — A little tub of screened worm castings or “black gold” being added to the new raised bed, from our worm bin. As you can see, a few friends came along for the party!

20% AERATION

An aeration addition is also key to healthy, effective soil. This could include lava rock, pumice, or perlite. Coarse sand also promotes aeration and drainage, but not quite as effectively as the others.

A lot of bagged soil mixes already contain aeration additives, which also includes things like peat moss or rice hulls. So if you use primarily bagged soil, read the ingredient list and adjust accordingly. You can likely go lighter on additional aeration (e.g. perhaps only 5-10% extra, if any).

Benefits of Soil Aeration

All the beneficial organisms found in soil need air to survive, including microbes, nematodes, worms, protozoa, fungi, and more. Even more, plant roots need air to thrive too! Plants breathe through their roots just as much as they do through leaves. That’s why it’s important to not overwater, and always provide drainage holes in pots. Otherwise, plants will drown!

An aeration additive also helps the soil achieve a ideal moisture balance. They create air pockets, promote good drainage, and prevent the soil from over-compacting. At the same time, they also increase moisture retention by absorbing water like a sponge, which helps the soil stay evenly moist for a longer period of time between watering.

Our Choice: Lava Rock

For the aeration portion of our raised bed soil recipe, we have come to love volcanic rock. It is also called “lava cinders” and is frequently used in aquaponics. Use the small 3/8 inch to quarter-inch size, not larger chunks! Lava rock is full of pores, that not only promote aeration and drainage, but are also the perfect habitat for beneficial microbes to grow. They don’t float to the soil surface like white bits of perlite do, and are generally more affordable than pumice.

Our local landscape supply company carries volcanic rock both in bulk and in half cubic-foot bags. If you can’t find volcanic rock, use small perlite or pumice. Availability of all these products will vary depending on your location.

A hand holding small red lava rock pieces, that are being added to the new raised bed. — 3/8″ lava rock – added for aeration, drainage, moisture retention, and surface area for microbial life!

How to Fill a Raised Garden Bed

Now that you have our raised bed soil recipe, it is time to fill them up!

We prefer to fill our garden beds 100% full of soil and compost. Aside from sometimes adding lesser-quality bulk soil to the bottom of our deepest beds, there’s no other “fillers” at the bottom. See notes about fertilizer additions or using hugelkultur (adding leaves or sticks to the bottom of beds) in the sections to follow.

As you fill the beds, try to mix all of the various ingredients as evenly as possible. We’ll generally add them in “lasagna layers”, mixing as we go. For example, add several inches of bulk soil or bagged soil, a good layer of compost, a couple inches of volcanic rock, and mix. With that, the bed may only be about quarter full. Repeat with more layers of each, mix. Continue this process until the bed is full.

Also, it’s best to fill garden beds with soil all the way to the top – giving the roots as much depth to grow in as possible. When you first water a new bed it will compact and sink down a little too. Depending on how much it sinks, you may want to top it off with another layer of compost or soil.

An image of a newly built redwood raised bed, only about half full at this time. In the bed, there is a combination of soil and compost, with some red volcanic rock on top, about to be mixed and then continued to be filled. — In the past, we’d add alternating wheelbarrows or bags of soil to create a “lasagna layer” of soil, compost, and volcanic rock, mixing in the layers as we go until it’s full.

Deanna and Aaron mixing soil in a planter with the help from a Kubota UTV whose bed has been used to dump bulk soil into the planter. — When creating our new garden, we rented a skid steer (tractor bucket loader) to scoop up the bulk soil and compost from the main pile in the driveway, load it into the back of our UTV, then drove it to the raised bed area to dump into each bed. We pre-mixed the soil, compost, and lava rocks in the UTV first by loading the material in alternating scoops, and then mixed it further by shovel as it was added to the bed.

What About Hugelkultur?

When filling a deep raised garden bed with soil, you can offset some of the cost by adding small logs, branches, leaves, mulch, pine needles, or other natural woody organic matter to the very bottom of the bed, and then add at least a foot of good soil and compost on top. The woody debris eventually breaks down to feed the soil as a carbon source over time.

This practice is called Hugelkultur . Learn hugelkultur pros and cons, best practices and materials to use, and how to make a hugelkultur garden bed here.

However, I do not recommend adding non-organic matter such as rocks, plastic bottles, styrofoam, or other random materials to take up space in your bed. I also don’t recommend using hugelkultur in shallow raised garden beds that are less than 12 to 15 inches deep.

A wood planter halfway full of logs and tree branches.

Adding Fertilizer to New Raised Beds

Most “virgin” soil (especially plain topsoil) should be amended with natural fertilizer to keep plants healthy, happy, and productive!

We prefer to use well-balanced, gentle, slow-release organic fertilizer like this one, lightly sprinkled and scratched into the top of the soil a couple times per year. When filling new beds, we also like to add a little Azomite rock dust for important trace minerals, which offer a vast array of benefits for plant growth!

If you fill raised garden beds primarily with high-quality organic bagged soils and compost, you can go pretty light on the fertilizer for the first growing season since the bags often contain amendments already. I always suggest using less than the manufacturer’s instructions in general. You don’t want to accidentally “burn” the plants!

On the other hand, if you started with mostly bulk soil and compost from a local landscape company, you’ll most definitely want to add fertilizer from the start. (That is, unless they say that it’s already amended, but I don’t think that’s common practice for most bulk material.)

Plants use up nutrients in the soil as they grow, so you’ll also want to implement a regular fertilizer routine for your raised garden beds going forward. In addition to adding slow-release fertilizer, we top off our raised beds with fresh compost and water with compost tea a couple times per year.

Sprinkling in a combination of kelp, alfalfa and neem meals to the top of the soil once the raised bed is full. This will be scratched into the top few inches of the soil, and watered in. We also added some rock dust here, and earlier when the bed was only half-full. — Sprinkling in a combination of slow-release fertilizer and rock dust to the top of the soil once the raised bed is full. This will be scratched into the top few inches of the soil, and thoroughly watered in.

The Importance of Mulch

Last but certainly not least, don’t forget to cover the soil with a couple inches of mulch. Mulch protects and improves raised bed soil by reducing evaporation, suppressing weeds, and buffering the soil (and plant roots) from temperature swings. We typically use a woody compost as mulch. Learn more about mulching best practices and pros and cons of 8 popular mulch options here, including bark or wood chips, straw, compost, and more.

A number of wood raised garden beds are shown, each planted out with various young seedlings and topped with woody compost mulch. There are various perennial flowering plants in the background along with cacti, vines, shrubs, and trees.

How to Improve Existing Raised Bed Soil

Do you have raised beds that are already full of soil that might not be the best quality, is having drainage issues, or the plants don’t seem to be growing very well? Don’t worry, it’s happened to us before too. But don’t feel the need to go dig out all your soil and start over. There is hope!

Before you consider replacing your raised bed soil, try amending it first using some of the materials we’ve discussed already, including compost, fertilizer, and more.

If your plants are sad and small, have you been fertilizing them adequately? Is your soil too compact? Try to loosen it up and mix in some aeration additions. Does it seem like the soil drains too quickly, or dries out too quickly? Add compost and worm castings! That, along with watering with aerated compost tea, will increase the microbial life in your soil. For better moisture retention, drainage, and “fluff”, peat moss or coco coir could also be mixed in. Note that coco coir is the more sustainable option of the two.

First, try those measures for a season and see if there is noticeable improvement. I really think there should be. If not? Next, consider taking out at least a portion of the old soil and replacing with the types of things discussed in this post.

The final raised garden bed for this example, now completely full of soil, compost, and aeration additions. It is being watered, with drips of water running down the side of the bed, and a rainbow has appeared in the water spray. — The final full bed. Make sure to give it some water to get everything happy, and to get those microbes kicking!

And that’s how we fill new raised garden beds with soil.

I hope that was helpful! If so, please consider leaving a review or comment below – and feel free to ask any questions! Now it’s time to put your new garden beds to good use. Don’t miss our guide on starting seeds indoors, tips for transplanting seedlings outside, or the best easy companion flowers to grow for pollinators!

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