What is the best way to fill a tall raised bed without spending a lot of money? The secret is to put your best soil where you need it and fill the rest of the container with other harmless materials. There are plenty of natural, organic, and synthetic options.
If you want to build one, use these free building plans for a tall raised garden bed.
Filling Tall Raised Beds: What To Use?
I love how tall raised beds elevate plants to new heights, showing them off in the garden. And, with everything easy-to-reach, there is less back strain.
But they also come with a problem—that’s a lot of space to fill and good soil is not cheap!
How can I fill this giant container without spending a fortune on soil?
It’s the same issue with large garden planters or urns. They look magnificent filled with flowers and trailing vines, but the potting mix can end up costing more than the plants.
So what to do?
There are a number of options to inexpensively fill the bulk of their bellies while still providing good growing medium right where the plants need it. This has tips for buying good garden soil.
Depending on what you are growing and your preferences, you might use natural, biodegradable materials like tree branches or stumps, or combine them with items like overturned bins or flower pots to help fill the void.
Alternately, you could build a false bottom in the raised bed, leaving the space below empty.
I’ve listed some things to consider first and provided a list of all sorts of materials that could work.
Contents
What to Consider First
For most plants, including many of the annuals and perennials we grow—not trees or shrubs—the roots occupy just 6 to 12 inches of soil.
This means we just need “good” soil in that upper layer and the rest of the container can be filled with something less precious or costly.
By “good” soil we mean some combination of soil, growing medium or potting mix, along with organic matter like compost or composted manures so there is healthy soil structure along with nutrients and microorganisms. That’s the place to spend money.
Anything below this layer can be (harmless) less-costly fillers so long as water can still drain freely.
Or, alternately you could build a shelf or false bottom within the raised bed to accommodate your plants.
You might also want to line the planting area with a porous landscape fabric to prevent the “good” soil from running away.
Whatever you choose, you’ll will need good drainage. Excess water needs to freely drain to the ground below.
Options For Filling Tall Raised Beds
Be sure whatever you choose is garden-safe and allows drainage.
If your raised bed has legs, choose lighter-weight items to avoid overloading it.
Natural Materials
- Top Choice: Wood stumps, branches, or logs.
I strongly prefer using natural materials whenever possible but there is one possible drawback.
Natural, organic materials (from living things) are biodegradable and will eventually decompose. Some are fairly fast-acting like leaves, while others like wood chips take longer.
Either way, decomposition means they slowly shrink which means the soil (or growing medium) up top may gradually sink and need replenishing.
It’s not a deal-breaker but something to consider if you’re planting long-living perennials. You may, at some point, have to dig them up, top-up the growing medium, and replant them.
This is not an issue for annuals or single-season vegetables since it’s routine to replenish the soil after each growing season anyways.
Options
- Coconut coir
- Composted manure
- Grass clippings
- Leaves – fall leaves or leaf mold
- Soil from another part of the garden or delivered in bulk
When I built my in-ground pond, the excavated soil filled several large raised beds. - Straw, straw bales
- Wool – raw, sheared wool
- Wood – stumps, logs, branches, twigs, tree trimmings, chips, untreated lumber
Processed Natural Materials
- Cardboard
- Paper
- Sawdust (from untreated wood only)
Natural Inorganic Materials
If you use these items be sure to leave pockets for water to freely drain through the container.
- Rocks, stones
- Seashells
Synthetic Materials
- Top Choice: Upside-down storage bins or plastic flower pots
Check your recycling bin! If you already have these things, they can be good, lightweight options for filling a lot of space with little effort or expense.
I personally prefer using only natural materials but it’s just not always possible and, if the alternative does no harm, go for it. We’ve got to fill the bed somehow!
Whenever using manufactured items, you have to think about any environmental ramifications and be sure they don’t leach or escape into the soil where they are essentially pollution.
A bunch of upside-down pots surrounded by lots of fall leaves can really fill the space nicely.
Options
- Packing peanuts (enclosed in large bags)
- Plastic bins, buckets, barrels, flower pots (upside-down)
- Milk cartons, jugs
- Soda bottles, cans
- Styrofoam
Build A False Bottom
- Create a shelf within the raised bed to accommodate 6 to 12-inches of soil.
If you don’t have fillers available, another option is to create a false bottom in the raised bed.
Add wood supports around the inner sides and insert wood slats strong enough to hold the weight of your plants and soil.
Or, use a bunch of strong, plastic flower pots to support wood boards to form a shelf.
You may also want to line the growing space with landscape fabric or grow in containers.
How Much Filler Do I Need?
If you’re buying soil as filler, you will need to know the size of your raised bed in cubic feet.
Make sure you’re buying good quality soil from a trusted source—not tainted fill.
Bulk orders of soil often come in cubic yards. A cubic yard is equal to 27 cubic feet.
This is the formula for calculating the size of your raised bed:
Length (feet) x Width (feet) x Height (feet) = Volume in Cubic Feet
If you are using the top foot of the container for good growing medium, omit 1-foot from the height before doing your calculation.
Examples
- 4 x 8-foot raised bed with 3-foot sides (count 2-feet of height)
4 x 8 = 32 x 2 = 64 cubic feet of fillers needed - 3 x 8-foot raised bed with 2-foot sides (count 1-foot of height)
3 x 8 = 24 x 1 = 24 cubic feet of fillers needed - 4 x 4-foot raised bed with 4-foot sides (count 3-feet of height)
4 x 4 = 16 x 3 = 48 cubic feet of fillers needed
Resources
How To Build A Tall Raised Bed (Free Building Plans)
Build A Raised Bed With Built-in Privacy Wall
What Is The Best Wood For Raised Garden Beds?
I hope this gives you some ideas. If you find tips like this helpful, consider subscribing to the free Empress of Dirt newsletter.
~Melissa the Empress of Dirt ♛
