How To Fill A Tall Raised Garden Bed Quick & Easy

Gardening with raised beds is one of my favorite methods. With raised bed gardening, you can easily control your soil type, your beds warm up faster in spring, weeds are fewer and easier to remove, and the soil stays loose rather than becoming compacted as it does in an in-ground bed.

But there is one drawback: figuring out how to fill a tall raised garden bed. It can feel daunting at first.

Whether you are using native soil, a custom soil mix, a blend of soil and compost, or something completely different, there are plenty of effective ways to fill a tall raised bed.

Large Modular Metal Raised Garden Bed Kit

Our Rating

Large Modular Metal Raised Garden Bed Kit – 29” Extra Tall

View At Epic Gardening

Small Modular Metal Raised Garden Bed Kit

Our Rating

Small Modular Metal Raised Garden Bed Kit – 29” Extra Tall

View At Epic Gardening

Round Metal Raised Garden Bed Kit

Our Rating

Round Metal Raised Garden Bed Kit – 15” Tall

View At Epic Gardening

Step 1: Decide What Your Bed is For

Before you start planning, decide how you want to use the bed. Some plants are much more shallow-rooted than others. For example, a red radish needs very little depth, while a daikon radish needs a couple of feet of soil.

Once you know the root depth you will be working with in each container, you can tailor your fill materials accordingly. Someone growing only leafy greens needs just six to eight inches of high-quality soil on the surface, with native soil or other materials below it to add bulk. Someone growing carrots will need at least a foot and a half of quality soil.

Drought-tolerant plants often develop deeper root systems, which allow them to reach further down in search of water.

Step 2: Choose a Size

I’m a huge fan of the Birdies raised beds. These raised beds are made from cold-rolled 22-gauge galvanized steel with an Aluzinc coating. This coating makes them extremely rust-resistant, allowing them to withstand whatever weather comes your way.

The taller your garden bed, the more material you will need to fill it. For example, the Round Tall Metal Raised Bed has a diameter of 38 inches, just slightly over 3 feet, and a depth of 29 inches. It provides about eight square feet of planting space on the surface, but requires 18 cubic feet of soil to fill completely.

Now let’s look at some of the other Birdies bed sizes, especially the Medium Tall raised bed. This model can be configured in multiple shapes, and when assembling your bed, you may wonder how much soil each configuration requires.

Below, we’ll go through the different layout options and how much soil each one needs to fill:

To compare that with other raised beds, my square beds measuring 4.5 feet by 4.5 feet by 24 inches take 40.5 cubic feet of soil, or 1.5 cubic yards, to fill. Birdies beds are not only sturdy, but they also offer excellent surface area while using significantly less soil than typical home-built wooden garden beds.

Step 3: Fill the Base

Before you fill a tall raised bed, lay down a one-quarter to one-half-inch layer of gravel underneath. This creates excellent drainage and protects the bottom of the bed. Another benefit of using gravel is that you will not battle weeds pushing up through the base during the season.

Because your highest quality soil goes on top, the material underneath needs to drain excess moisture efficiently. Avoid using rocks or large stones at the bottom of your raised bed, as these can create an artificial water table that prevents proper drainage. Good drainage is essential in raised garden beds.

Organic Materials to Use

Old, dry wood makes a suitable base layer to fill a tall raised bed, since it will slowly decompose beneath the soil. Wood also holds some moisture while still allowing excess water to drain away.

It takes a couple of years for old branches or small logs to break down, so keep that in mind. Avoid planting deep rooted vegetables in wood-filled beds at first, and stick to shallow-rooted crops. Using wood in this way is a variation of a technique called hugelkultur.

Other forms of garden waste also work well as a base layer. Grass clippings, dry leaves or leaf mold, prunings, and similar materials can fill the bottom of the bed. These break down quickly and help build organic content in the soil. However, as they decompose, the soil level drops, often noticeably by late season. Even so, this is an excellent way to start a new raised bed, and you can add more soil later as needed.

If you have a compost pile that is not fully finished, add that half-decomposed compost to the bottom to fill a tall raised bed. It will continue breaking down there. You can mix in some local garden soil if you prefer, but it is not necessary. These lower layers are also useful places to bury bokashi, covering it with grass clippings or other garden waste before adding soil on top.

Step 4: Customize Your Soil Mix

Now that your base is in place and you are ready to add the growing layer, it is time to decide what you want to plant in. This top layer sits above your fill material and is where your plants will receive most of their nutrients and moisture.

A popular raised bed soil blend is Mel’s Mix, which contains equal parts blended compost, peat moss, and coarse vermiculite. It works beautifully in many raised beds, but only when the bed sits on a surface that drains well. If your raised bed is on concrete or hard packed clay, choose a mix with better drainage. Adding perlite improves drainage, and if you prefer a sustainable option, rice hulls make an excellent perlite substitute.

When I built my own beds, I used a custom blend for the upper layer to fill a tall raised bed. It included composted dairy and chicken manure, leaf and plant compost, vermicompost, sandy loam, aged forest humus, peat moss, wheat straw, and screened local topsoil. It performed incredibly well, although the high organic content caused the soil to settle by almost a third over the first year as everything broke down.

What’s the Best Soil for Raised Beds?

Many people wonder whether there is a “perfect” blend for raised beds. The truth is that it depends on your local materials, your climate, and the crops you plan to grow. You can certainly use a bagged planting mix made for raised beds, and it will work, but depending on your weather and growing conditions, it may not be ideal.

In my experience, many premade mixes do not retain enough moisture to keep plants alive during scorching summers. If you live in a rainy or cool climate, you may need additional drainage instead. Customize your soil blend so it works for both your climate and your gardening goals.

If you are growing food crops, there is another important consideration. Many vegetables are heavy feeders, so your soil needs plenty of rich compost or fertilizer. I like to use composted dairy manure and worm castings blended with peat moss or coconut coir and some local soil. With high quality compost, you may not need to use any fertilizer until the following season.

Step 5: Replenish Your Raised Bed Annually

Every fall, I gather as many fallen leaves as I can, shred them with my lawnmower, and spread a deep layer of leaf mulch over any inactive beds. Worms work through the leaves over winter, creating a rich, humusy surface layer that plants absolutely love. Leaf mold like this is one of the best organic additions you can make to a raised bed.

You can also top off your raised bed in fall using a lasagna layering method. Alternate green, fresh materials with brown, dried materials. Greens include alfalfa hay, vegetable scraps, and grass clippings. Browns include dry straw, fine wood chips, and dry leaves.

Lay down a brown layer, then a green layer, and if you choose, add a manure layer on top. Continue layering until the bed is full, even mounding it slightly above the rim. By spring, you will have a beautiful planting surface that helps refill and enrich your bed.

I use a variation of the lasagna method with specific ingredients. I select high nitrogen materials such as certified weed seed free alfalfa hay and chicken manure and alternate them with dried leaves and pine shavings.

Once I have six to eight layers built up, I finish with about three inches of composted manure, then put the bed to rest by covering the surface to stop weed seeds from blowing in. Landscape fabric works well for this.

When spring arrives, I remove the landscape fabric. There will usually be an inch or two of material that has not fully decomposed, matted beneath the manure layer. I use the tip of a trowel to create planting holes through this matted layer and plant directly into the openings. Avoid disturbing the rest of the mat, as it helps keep the soil moist. By repeating this each fall, you will significantly improve your raised bed soil and boost spring yields.

Alternatives

If you do not want to try composting directly in your raised beds, that is perfectly fine. You can simply add more soil and compost as needed each year. I like to mix in coconut coir or peat moss for added moisture retention. If I need extra drainage, I add perlite or rice hulls.

Using a wood chip mulch during the growing season to fill a tall raised bed also creates a slow form of composting. Fine wood chips gradually break down, adding organic bulk to the soil, and they work their way downward to improve drainage as well.