How To Fill A Short Raised Garden Bed

With raised garden beds becoming the preferred format for many gardeners, the topic of how to fill a short raised garden bed is paramount. Choosing the right garden soil and the appropriate amendments are important. The organic material you choose determines how your entire season progresses. 

You may have a thriving compost pile to help you fill your raised bed. Perhaps you want to try filling raised beds with a garden bed soil mix, or maybe you want to build your own with a regenerative technique that relies on a supply of organic matter. Whichever you choose, we’ve got you covered. 

Filling raised garden beds doesn’t have to be hard or expensive, depending on what you have around. Here, we’ll discuss how much soil you need, and how to fill a raised bed that is short!

What Is Your Short Raised Garden Bed For?

To determine which materials will fill raised garden beds you’ve placed in your yard, you’ll first want to decide what to grow. Most raised garden beds will do just fine with garden soil formulated specifically for them. However, you can add amendments that cater to the plants you’re growing. 

For instance, homemade compost is an excellent source of micronutrients for most plants. Peat moss can help you retain moisture in your raised beds. Native soil will provide beneficial bacteria and mycelia that exist within the soil profile of your region. Mulching with wood chips, grass clippings, or leaves to lock in moisture and protect roots from extreme temperatures may be a concern too. 

Maybe there’s a raised bed gardening technique you’d like to try that involves layering organic materials before topping off your short raised bed gardens with soil where plants can grow. Consider these things before you purchase fill materials.  

How Much Material Do I Need?

The material you’ll need for filling your bed depends on the bed size you’re filling!

With the Birdies Original Raised Beds available through the Epic Gardening shop, we’ve already done the math for you on each of the configurations available. You’re welcome to use our chart on each bed’s page to estimate the amount of soil you need.

But if you built a DIY raised bed, here’s a certain formula that’s widely used to calculate the volume of your raised bed and how much soil you’ll need:

Width x Length x Height = Total cubic feet of fill material.

Begin by measuring each of the dimensions of your bed in feet. If you end up with a bed that isn’t exactly measured in feet, round up as this ensures you’ll have more than enough soil on hand to fill it when the time comes!

To illustrate my point, let’s say you’ve got a new garden bed that is roughly 4 feet wide, 8 feet long, and 1 foot deep. The calculation for that bed would be simple: multiply 4 x 8 x 1 together, and you’ll discover you’d need 32 cubic feet. If you’re buying soil in bulk, that comes out to 1.19 cubic yards of soil, so you’d want to buy at least 1.5 cubic yards to be sure you have enough to fill and have leftover. (And you’ll want that leftover soil to top off other beds later or use for containers!) Those buying bagged soil will generally be able to find bags in 1.5 or 2 cubic foot sizes; assuming you’re using 2 cubic foot bags, you’d need 16 bags of soil to fill that bed completely.

If your bed was 4.5’ x 8.5’ x 1’5’, getting that same amount of garden soil would leave you considerably short. Garden beds are meant to be full, and those small amounts of space add up quickly, especially once you’ve watered the soil in and it settles! I highly recommend getting enough extra soil to top off your garden beds later.

As the initial soil settles into place and fills every square inch of space, it will sink down in the bed by many inches. Deep beds may still have ample space for roots, but you’ll probably need to top it off in shallow beds to keep a productive garden going. A few inches of soil can make a world of difference!

A Word on the Planting Area

Before we get into the specifics of how to fill your brand new raised bed, let’s cover a couple of basic rules of thumb. Firstly, no matter what method you use, remember to provide no less than 8 to 12 inches of soil dedicated to planting. If you’re using an Original Birdies bed, you have some room to work with as the shorter Birdies beds are 15″ in height.

When using an even shorter raised bed that’s only 8 inches tall, do not use fill materials and devote the entire space to planting. If your bed is less than 8 inches, you’ll need to dig a trench with no fill below to improve the soil and allow for adequate aeration of the soil where roots can grow.

Ways to Fill Your Short Raised Garden Bed

Let’s discuss different ways to fill your raised beds that can assist you in building great soil. Of course, there are more ways to fill a raised bed garden than are presented in this piece, but we wanted to cover a few of the most cost-effective ways to do so.

Before you fill your bed, lay down a 1/4 inch to 1/2 inch of gravel underneath. This allows for excellent drainage and protects the bottom of the bed. Another great benefit of using gravel under the bed is you won’t struggle with weeds throughout the season. 

The basis of many of these gardening methods is they provide you and your plants with raised bed soil that is nutrient-rich and is continuously replenishing. That means you won’t have to do as much maintenance to keep up your filled raised beds from year to year. 

Hugelkultur

The hugelkultur method is one of the best ways to build healthy soil and save money at the same time. The process is simple. It involves laying a base of large rotting logs and then topping them off with smaller branches, then twigs. As you layer, you fill in holes between logs and branches with kitchen scraps, compost, leaves, and sometimes leftover potting soil. Then you top it all off with a substantial amount of high-quality soil for a fall or spring planting. 

As the rotting debris beneath the soil surface breaks down, amazing soil is being built underneath. This fertile soil is exceptionally suited for retaining moisture and nutrients in your raised bed garden. 

There are a few things to note when you fill a raised bed with a hugelkultur. First, a hugelkultur raised bed will require that you keep more soil on hand because your soil level will reduce quite a bit in the decay process. Adding soil throughout the process is important. Another thing to note is to leave at least eight inches of room above your rotting material. This allows you to have planting holes deep enough for root vegetables if root crops are your desired output. 

To do this, you’ll need to dig a trench within the perimeter of the bed before you lay your large base logs to have enough space for plantings above. Lay the logs in the trench, and layer, ensuring you have that 8-inch buffer before you plant starts or seeds.     

Core Gardening

Another awesome organic gardening method used to fill raised beds is the core gardening method. A core garden uses straw bales as the main material to fill a raised bed. 

Much like the hugelkultur method, you’ll want to dig a trench that is at least a foot deep to allow adequate space for the hay, and your planting area above (at least 8 inches deep, remember?). Some hay has weed seeds in it, so source it wisely. We have an awesome GardenStraw product in the Epic Gardening shop that could serve as your hay source.  

Then add about 5 inches of organic matter on top of the straw or hay. This could be composted manure, organic compost, or scraps from your compost bin. Above that, you’ll lay your soil blend, whether it be bagged soil or a mix you developed yourself from peat moss, worm castings, coarse sand, etc. 

What you are doing is creating a compost bin inside your raised bed. As the material breaks down beneficial microbes feed on the organic matter, creating beneficial relationships between plants and soil. 

Lasagna Gardening

Another great regenerative method for a regenerative filling of a raised bed is lasagna gardening also referred to as sheet mulching or the mulch queen method. If digging a trench isn’t your style or preferred method, you can simply lay down materials that create rich soil when broken down. This popular gardening method is the easiest on the offset, as it doesn’t require tilling or digging in the earth.

You begin by placing cardboard directly on the ground. This layer should be devoid of tapes, adhesives, and most metals (staples and fasteners). So take some time to remove these before putting the cardboard down. Use cardboard that doesn’t contain a lot of chemicals or dye, as these can affect the growth of your plants above. 

Then lay your raised bed on top of the cardboard. Follow up with a few layers of green and brown matter. Green matter is living tissue from kitchen scraps, compost, and composted animal manure. Brown matter comes from small branches and twigs, dried grass clippings, and dead materials like dried shredded leaves. 

A thick layer of small branches and twigs on top of your cardboard base provides good drainage to the bed. Follow that up with a layer of organic mulch twice the size of the base. Water these layers, and add compost that’s about half the size of your base layer of twigs. Top it all off with a layer of mulch, and you should be able to plant directly into the bed after a couple of days. 

If you’d like to further develop the sheet mulching technique, you can dig into the earth to give yourself a little more room to work with. How much space you have should be determined by how much material you want to use. 

Filling the Bottom of Your Short Garden Beds

I should mention it’s entirely possible to mix and match these methods or partially do one of these, adding a layer of quality soil on top. You’ll still have the beneficial microbial content but at a less regenerative level.

If using a regenerative method isn’t possible in your timeframe, no problem at all. You can layer drainage materials acquired in gardening stores before adding quality soil for planting above. Plenty of materials can wick moisture away from the soil, providing good drainage to the bed. We mentioned using a layer of branches at the base of your bed in the lasagna mulching section.   

Base Materials to Avoid

It’s important to avoid using non-porous rocks, which can create a water table at the base of your beds and create conditions where diseases can take hold. You want something that can break down easily, and create a decomposing basis for your bed. This is the source of beneficial soil microbes.

You do, however, want to layer that gravel before you place your bed!

Short Raised Bed Custom Blends

Once you have your base covered, it’s time to consider what to put within the planting layer of your short raised bed. When you acquire your materials, ensure you have enough to satisfy the cubic feet parameters of the bed. 

Many gardening stores sell raised bed blends. These are usually suitable for growing most annuals, but you may need to consider amendments suited specifically to your garden. Coconut coir and peat moss retain moisture in the bed while providing drainage simultaneously. Rice hulls are another viable option, aerating the soil, and creating a lightweight material that earthworms can easily navigate. 

Lava rock is a porous material that can act much like perlite and vermiculite in a raised bed, providing excellent drainage and making so you don’t have to water as often. Worm castings are a similar material that is highly beneficial for your short raised bed. These have been known to promote better growth and yields overall. 

Then, there are smaller amounts of material catered to specific plants. For instance, if you’re growing acid-loving plants like blueberries or sweet potatoes, additions of extra peat moss, pine needles, and cottonseed meal can lower the pH, increasing acidity in the soil. 

Animal manures are great when you need a lot of organic content. Plants that benefit greatly from cow manure include turmeric and ginger. What you want to avoid, though, is fresh animal manure, which can burn plants and contain seeds that can sprout in your beds. Make sure that your manure has been adequately composted before adding it.   

Replenishing Your Short Raised Bed Annually

The most basic form of replenishing your short raised bed is by simply adding more of a soil mix you know works best for your situation. However, a few other ways to do this might provide a better soil profile for the next season’s crops. 

A small lasagna-style layer can give you a good variety of nutrients that your existing soil microbes will love. Even a thick, even layer of mulch has a similar effect. You can let the mulch break down, providing you with rich material for the next season. You could compost on top of the soil or make a small hugel mound that will break down over the next few months. 

Whatever way you decide to go, there are options. It can be as expertly crafted or thrown together as you want, and it can be as expensive or cheap as you need it to be.