Quick answer
A raised garden bed is a growing area filled with soil and held above the surrounding ground by a frame or a mound, so plant roots sit in a soil you chose rather than in the native ground beneath.
People build them for drainage, for access and for sites with poor or suspect soil. The frame material and the fill both matter, and extension offices ask you to test a questionable site before you plant food in it.
Quick facts
The key facts about Raised Garden Bed, with sources:
- Width
- 4 feet is a convenient width, so the center is reachable from both sides, per the University of Delaware 1
- Depth
- At least 1 foot, per the University of Delaware 1
- Paths
- At least 4 feet for walking and wheelbarrows, per the University of Delaware 1
- Sunlight
- At least six hours of direct sun a day, per the University of Delaware 1
- Arsenic-treated wood
- CCA lumber has not been available for residential use since 2004, per the University of Maryland 2
- Lead tiers (UGA)
- Under 75 ppm: grow directly in soil. 75 to 400 ppm: raised bed or barrier, no root crops. Over 400 ppm: consider another site 5
- Do not use
- Recycled tires, or lumber treated with creosote or pentachlorophenol such as railroad ties 1
Key takeaways
- A raised bed holds chosen soil above the ground. It helps drainage and access, and it is a common answer to compacted or suspect soil.
- Plan a width you can reach across, at least 1 foot of depth and a spot with six hours of direct sun, according to the University of Delaware.
- Extension offices agree on one hard rule: no railroad ties, tires or creosote and pentachlorophenol lumber. They differ on how cautious to be about modern pressure-treated wood.
- If the site is old, urban, near a painted building or near a road, test the soil for lead before you plant food. A raised bed over bad soil still needs a barrier.
- Call 811 before digging at the site, and ask your local Cooperative Extension office before buying large amounts of fill.
A bed you build up instead of dig down
A raised bed is a frame, or sometimes just a mound, filled with soil. The University of Delaware says a raised bed lets roots develop in soil held above waterlogged, potentially contaminated or compacted sites. You can mix in compost and other organic material to help drainage 1.
The same source lists the advantages. Soil warms faster in spring, the bed can be covered to start early or extend the season, a taller bed means less bending, and a raised bed can make gardening possible in small spaces or where paving and poor soil would otherwise block it 1.
This page covers the bed itself: its size, its frame and its fill. For preparing ordinary in-ground beds, see landscape bed preparation. For a hired planting job, read our planting and garden beds guide.
Two things are easy to overlook. A frame does not clean the soil under it. And a bed sitting on top of old paving or contaminated ground may need a barrier below the fill, which the Delaware guide describes 1.
How a raised bed works: frame, barrier, fill and water
The frame. It holds the soil in place and sets the height. Delaware lists cedar, cypress, recycled lumber, cinder blocks and bricks, and says new pressure-treated wood such as pine is safe but should not be considered for organic gardening 1. The next section compares what the sources say about each material.
The barrier. When building on suspected or confirmed contaminated soil, asphalt or concrete, Delaware says to use a barrier fabric between the bed and the ground, and it recommends geotextile fabric 1.
The University of Maryland describes a different use: a heavy plastic liner between a treated frame and the soil, which it says still lets the soil drain 2.
The fill. Delaware says to fill the bed with a good quality topsoil and compost blend, or a raised bed bag mix, and calls soil the foundation and most important ingredient 1. The difference between the two main ingredients is on our compost vs. topsoil page.
The ground below. Delaware says to sample the soil at the site, remove existing vegetation if the soil is healthy, loosen compacted ground so it can drain, then level the area before building 1.
Water still has to move out of the bed, which is why a bed on solid paving needs a plan for the runoff. See soil drainage and infiltration.
- Plants and mulchPlants sit in the fill; a mulch layer is optional
- Fill: topsoil and compost blend, or a bagged raised bed mixDelaware calls soil the most important ingredient 1
- FrameCedar, cypress, recycled lumber, block or brick, per Delaware; see the materials table 1
- Barrier fabric or liner (as needed)Geotextile over contaminated ground, per Delaware; plastic liner between treated wood and soil, per Maryland 12
- Loosened native groundBreak up compacted soil so water can drain, per Delaware 1
Layers follow the University of Delaware and University of Maryland guides. Which layers you need depends on the site and the frame. Source: [1] [2]
Frame materials compared, as extension offices describe them
| Material | What the sources say | Who says it | Watch for |
|---|---|---|---|
| Cedar or cypress | Good choices because they are naturally insect and decay resistant; Maine names untreated hemlock or cedar as a rot-resistant choice that lasts several years before replacement | Delaware 1; Maine 3 | Replacement time varies with wood and climate |
| Other decay-resistant woods | Cedar, black cherry, oak, black locust, Osage orange and redwood are listed | Maryland 2 | Availability depends on region |
| New pressure-treated lumber | Safe but should not be considered for organic gardening, per Delaware. A judgment call, per Maine, which says plants take up relatively little and the main concern is gardener contact with soil | Delaware 1; Maine 3 | Check the tag for the preservative; see the next row |
| Copper-based treatments (MCA, ACQ) | MCA has no arsenic but contains copper, and Oregon State research found raised soil copper only within 1 inch of the bed edge. Penn State, as summarized by Oregon State, recommends ACQ, which contains no arsenic, chromium or any other chemical considered toxic by the EPA | Maryland 2; Oregon State 4 | Maryland’s page does not mention ACQ; Oregon State’s page is a 2013 piece reviewed in 2024 |
| Old CCA lumber | Arsenic has been the main concern. CCA has not been available for residential use since 2004 | Oregon State 4; Maryland 2 | Reused older timber may be CCA |
| Creosote, pentachlorophenol (railroad ties), tires | Do not use | Delaware 1; Georgia says old treated lumber, railroad ties and utility poles may contain arsenic, chromium or creosote 5 | Salvaged timber of unknown origin |
| Stone, brick, concrete block | Listed as options. Blocks often include fly ash, a coal byproduct that Maryland says contains heavy metals; labels do not name the aggregate, and sealing with polymer paint is one option | Maryland 2; Delaware 1 | Unknown block content |
Low risk is not zero risk
Maine calls pressure-treated wood a judgment call and says the treatments are much safer than in past decades, but the risk is not zero 3.
Oregon State says the chemicals leach in very small amounts and it cites no research showing levels that threaten health 4.
If you want to skip the question, pick untreated rot-resistant wood, block or brick.
Size, siting and building steps
Delaware gives the plainest sizes. Width: 4 feet is convenient because the center is reachable from either side and wood is sold in that length.
Length: typically 4 feet or twice that at 8 feet. Depth: at least 1 foot to hold enough soil. Make the paths at least 4 feet wide for walking and wheelbarrows 1.
Depth is not the same for every plant, and we did not find a university chart we could verify, so we do not print one. Taller beds can suit gardeners who have difficulty bending or use a wheelchair, Delaware notes 1.
Siting: Delaware says the bed must receive at least six hours of direct sun a day, preferably in a north-south orientation, with good drainage and easy access to water 1.
For how sun terms work, see sun exposure for landscape plants. For how far apart to plant inside the bed, see plant spacing.
Timing: Delaware says the best time to build is in fall or early winter, without working soil that is too moist, so the fill settles by spring 1. That is one state’s advice. Your climate may differ.
Example: how much fill a bed holds
The bed sizes below are invented, built from the length and width Delaware calls typical 1. Volume in cubic feet is length times width times depth in feet. A cubic yard is 27 cubic feet. This is arithmetic, not a soil recommendation.
| Bed (example) | Depth | Volume in cubic feet | Volume in cubic yards |
|---|---|---|---|
| 4 ft by 8 ft | 12 in. (1 ft) | 32 | about 1.19 |
| 4 ft by 8 ft | 18 in. (1.5 ft) | 48 | about 1.78 |
| 4 ft by 4 ft | 12 in. (1 ft) | 16 | about 0.59 |
| 4 ft by 8 ft | 24 in. (2 ft) | 64 | about 2.37 |
Remember that fill settles
Delaware notes a bed built in fall will have settled by spring 1. Plan to top up rather than overbuy on day one, and ask your local Extension office about mixes for your area.
The step from 12 to 24 inches doubles the fill. Delaware says the soil is the most important ingredient, so the volume is where a bid or a budget can swing.
Our mulch calculator uses the same area-and-depth arithmetic for any loose material. Ask the supplier what the product is made of, not only how much of it you get.
Where the term shows up: kits, bids and planting plans
Retail kits. Delaware says raised bed kits are often pricier but include all materials 1. Check the wood type and the finish on the tag.
In a bid. Look for frame material, height, liner or fabric, number of cubic yards of fill and who supplies it. Our landscaping estimates guide shows how to compare lines.
In a design. Raised beds often appear in a plan as edible beds, cutting gardens or accessible beds. See landscape design.
In an HOA or city rule. Some associations limit height, placement or materials. See our HOA landscaping research.
What a raised bed does well, and where it falls short
What it can do
- Holds roots above waterlogged, compacted or poor ground, and lets you choose the soil 1.
- Warms faster in spring and can be covered to extend the season 1.
- Reduces bending, depending on the height 1.
- Works as a mitigation for some contaminated sites. UGA lists a raised bed or a barrier for lead between 75 and 400 ppm, along with avoiding root crops 5.
What it cannot do
- It does not clean the ground below. Above 400 ppm lead, UGA says to consider relocating the garden 5.
- It does not suit every site. It needs the sun, the water access and the space that Delaware lists 1.
- It takes materials, soil and a place with enough sun and water access 1.
- A bad frame choice adds a problem instead of fixing one.
Limits and open points
Extension offices disagree on pressure-treated wood. Delaware says it is safe but not for organic gardening, Maine calls it a judgment call, and Oregon State says it cites no research showing levels that threaten health 134. We do not pick a winner. We show the range.
The Maine page does not name CCA or ACQ, and the Maryland page does not mention ACQ. The ACQ statement is Oregon State’s summary of a Penn State publication, which we did not read directly 324.
The UGA lead tiers are one state extension’s reading of federal guidance. We tried to read the EPA fact sheet, but our request was refused, so we cite UGA only 5. We also do not give a depth for each plant, and we did not find a verified watering interval.
A soil test only sees what it is asked to see. UGA says lead is the most common contaminant in urban soils and suggests contacting your local Extension office for sample bags and for help reading results 5.
What drives the cost of a raised bed
We do not print prices on a glossary page. These are the things that change a bid or a shopping list.
Frame. Cedar, cypress, block and kits differ in price and durability. Delaware says availability, price and durability are the three factors to weigh 1.
Height and footprint. A taller bed needs more fill, more frame and more hardware. The example table above shows the volume doubling from 12 to 24 inches.
Fill. Bulk blends and bagged mixes cost differently, and delivery matters. Ask for the source and a description of the blend.
Site work. Loosening compacted ground, leveling, barrier fabric, liners and paths all add lines 1.
Testing. A lead or metals test is a lab fee that varies. Ask your Extension office.
Lifespan. Maine says untreated hemlock or cedar lasts several years before replacement, based on one educator’s own beds, which are 6 to 7 years old 3. Other woods and climates differ. See the cost hub and our landscaping cost estimator.
Care after the bed is built
Soil in a new bed settles, so expect to add some in the first season. Add compost and organic material as Delaware suggests for drainage and growth, but check any product for what it contains 1.
Watch the frame. Wood in contact with wet soil rots over time, and Maine’s one example shows hemlock lasting at least 6 to 7 years in one educator’s garden 3. Replace boards before they fail so the soil does not spill out.
If you used a liner, Maryland says it lets the soil drain, so check that water is not trapped in the corners 2.
Maine says the main concern with treated wood is direct contact with the soil, through skin, inhalation or accidental ingestion, and it points to an Iowa State piece that suggests protective gear during installation and a sheet plastic barrier as a liner 3.
Our mulch types page covers mulches on top of the soil, and landscape edging covers the border around beds.
Warning signs and when to get help
Before you build. Stop and test if the site is near an old painted building, a busy road, a former industrial lot, or fill of unknown origin. UGA says lead is the most common urban contaminant 5. This page is not a diagnosis of any site.
After you build. Look for stunted plants, a smell, an oily sheen or anything odd about the fill. Do not eat from the bed until you know what is in it.
Get help. Contact your local Cooperative Extension office for sample bags and for help reading results, as UGA advises 5. For soil removal, grading or a bed against a house wall, hire a qualified company. Use our guide to choosing a landscaping company.
What is regulated, and what is only advice
| Topic | What is stated | Type | Source |
|---|---|---|---|
| CCA lumber | Not available for residential use since 2004; the EPA restricted it that year | Federal action; as reported by extension offices | Maryland 2; Oregon State 4 |
| Frame material choice | Extension advice, not law | Guidance | Delaware 1; Maine 3 |
| Lead tiers for gardens | Under 75 ppm, 75 to 400 ppm, over 400 ppm | Extension guidance, based on federal guidance we did not read directly | UGA 5 |
| Height, setbacks, materials | Set by local ordinance or HOA | Local law or private rule | Check locally |
Raised bed compared with related ideas
| Idea | The difference | Where to read more |
|---|---|---|
| Raised garden bed (this page) | A framed or mounded bed of imported soil above grade | You are here |
| In-ground bed | Plants grow in prepared native soil at ground level | Covered in the first section |
| Topsoil fill vs. compost | The two main ingredients of the fill | Covered under how a bed works |
| Soil testing | A lab or kit result for nutrients and contaminants | Soil testing |
| Planting service | A company that installs beds and plants | Covered in the first section |
Myths about raised beds
- Myth A raised bed protects you from bad soil underneath.
- Reality It helps, but UGA says above 400 ppm lead you should consider relocating, and Delaware says to use barrier fabric over contaminated ground 51.
- Myth All treated wood is the same.
- Reality Old CCA contained arsenic, while MCA does not but contains copper, and ACQ has no arsenic according to Oregon State 24.
- Myth Any old timber is a free frame.
- Reality Delaware says never to use railroad ties or lumber treated with creosote or pentachlorophenol, and UGA says to avoid old treated lumber and utility poles 15.
- Myth Concrete block is always inert.
- Reality Maryland says blocks often contain fly ash, which includes heavy metals, and labels do not name the aggregate 2.
- Myth Deeper is always better.
- Reality Delaware says at least 1 foot; we found no verified source that says deeper is better for every plant 1.
What changes by region: climate and the site’s history
Two things vary. The first is climate. Delaware’s advice to build in fall or early winter, and its note that soil warms faster in spring, come from a mid-Atlantic state 1.
A hot dry region, a cold short-season region and a humid region will not follow the same calendar, and the USDA hardiness zone is only part of the picture. The second is the site’s history.
Lead and other metals are a feature of old buildings, roads and fill, not of a state, so the test result for your lot is the variable.
Your local Cooperative Extension office or state lab runs the tests and reads the result.
When to build one, and your next step
A raised bed makes the most sense when the soil is compacted, soggy or doubtful, when you want to grow food in a small space, or when you want a bed that is easier to reach.
Your next step is to pick the spot with at least six hours of direct sun and a water source, then sample the soil if there is any chance of contamination.
Choose a frame from the materials table, build the bed to a width you can reach across, and fill it with a topsoil and compost blend you can describe.
If you want help with the planting, read the planting guide linked at the top and find a landscaping company. HyreYard does not build beds.
- If Lead under 75 ppm
- Then UGA says it is safe to grow food directly in the soil; a bed is still fine for drainage or access 5
- If Lead 75 to 400 ppm
- Then Install a raised bed and/or a barrier such as mulch or plastic over exposed soil, and avoid edible root crops 5
- If Lead over 400 ppm
- Then Consider relocating the garden 5
- If Site is suspect and untested
- Then Test first. Use barrier fabric under any bed on contaminated ground 1
Questions about Raised Garden Bed
What is a raised garden bed?
It is a growing area filled with soil and held above the surrounding ground by a frame or a mound. The University of Delaware says it lets roots develop in soil held above waterlogged, potentially contaminated or compacted sites, and lets you mix in compost to help drainage.
How deep should a raised garden bed be?
The University of Delaware says at least 1 foot, enough soil to grow a healthy, productive garden. Taller beds can suit gardeners who have difficulty bending. We did not find a verified university chart that gives a depth for each plant, so match your crops with your local Extension office.
How wide should a raised bed be?
The University of Delaware calls 4 feet a convenient width because you can reach the center from either side. Length is typically 4 feet or 8 feet. Keep paths at least 4 feet wide for walking and wheelbarrows. Narrower beds are easier on the soil, since you do not step in them.
Is pressure-treated wood safe for raised beds?
Sources differ. Delaware says new pressure-treated wood is safe but not for organic gardening. Maine calls it a judgment call and says plants take up relatively little. Oregon State cites no research showing levels that threaten health. Untreated cedar or hemlock avoids the question.
What wood should you not use for a raised bed?
Do not use railroad ties or lumber treated with creosote or pentachlorophenol, and do not use recycled tires, says the University of Delaware. Georgia’s extension adds old treated lumber and utility poles, which may contain arsenic, chromium or creosote. Older CCA lumber also raises concern.
What is the best soil for a raised garden bed?
The University of Delaware recommends a good quality topsoil and compost blend, or a raised bed bag mix. It calls soil the foundation and most important ingredient, and suggests asking your local Extension office about mixes and the amount you need.
Do I need to test the soil before building a raised bed?
If the site is old or urban, yes. Delaware says to sample the soil to be sure the site has healthy soil. UGA says lead is the most common urban contaminant and that Extension offices can provide sample bags and help with results.
Do raised beds protect against lead in soil?
They can help. UGA says at 75 to 400 ppm lead, install a raised bed and/or a barrier and avoid edible root crops, and above 400 ppm consider relocating the garden. A bed does not clean the ground below, so fill and barrier matter.
How much sun does a raised bed need?
The University of Delaware says at least six hours of direct sunlight a day, preferably with a north-south orientation, plus good drainage and easy access to water. Some crops need more or less, so check each plant’s tag.
When should I build a raised bed?
The University of Delaware says the best time is fall or early winter, without working soil that is too moist, so the soil settles by spring. That is advice from one state. In another climate, ask your local Extension office what suits your season.
Sources
- University of Delaware Cooperative Extension, Raised Bed Gardening (Carrie Murphy, Extension Educator, October 2024), PDF read as text with pdftotext, retrieved .
- University of Maryland Extension, Safety of Materials Used in Building Raised Beds (updated March 29, 2024), retrieved .
- University of Maine Cooperative Extension, Ask the Expert: Is it safe to use pressure-treated lumber for raised garden beds? (Jonathan Foster, April 3, 2024), retrieved .
- Oregon State University Extension, Raised bed lumber, pressure treated safe? (Scott Leavengood, August 2013, reviewed 2024), retrieved .
- University of Georgia Extension, Urban Gardening: Assessing Soils for Contamination (Circular 1075, full review July 11, 2025), retrieved .
- USA North 811, DIYers (call 811 before you dig), retrieved .
Expert review
Written by the HyreYard Research Desk. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Bed dimensions, frame materials, barrier fabric, fill and siting come from the University of Delaware guide (October 2024), read as text from a PDF.
Treated-wood safety comes from Maryland, Maine and Oregon State extension pages, which disagree, and the page shows the range. Lead tiers come from UGA Circular 1075; the EPA fact sheet it draws on was not readable to us.
The ACQ statement is Oregon State’s summary of a Penn State publication we did not read. Bed sizes and volumes are invented examples with labeled arithmetic. No prices or depths for specific plants are given.
Suggest a correction. We fix errors and say what changed.