Building Planter Boxes Out of Pallets: Check the Stamp First
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Updated 19 October 2026 | Author: Editorial team, homelycapers.com
Building planter boxes out of pallets is a reasonable project only when you can confirm how each pallet was treated, and that check decides the answer more than the carpentry does. Most people who search for building planter boxes out of pallets want two things: to know whether the wood is safe around edible plants, and to know whether a simple box will hold soil. This guide answers both in order. Read the pallet markings first, choose the wood treatment for the box second, then size and drain the box. Each step below follows what the university sources we opened say.
Quick answer
- Read the stamp before you cut. The Ask Extension answer lists HT, DB and KD pallets under “Pallets that are safe for use in vegetable gardens,” and lists MB pallets under “Pallets that should not be used in vegetable gardens.”
- Reject unmarked or unknown pallets for food plants. Ask Extension says an unmarked pallet “may be safe to use,” but adds that “It is better, however, to reject a pallet without origin and treatment information.”
- Size the box from board height. Iowa State says 11 inches is a common height because it equals two 2×6 boards, whose actual size is 1.5 x 5.5 inches. Each stacked board adds about 5.5 inches.
- Line the inside if the wood is treated. Iowa State says treated wood may need its inside lined with fabric that lets water drain while keeping soil roots away from potentially toxic chemicals.
Why the pallet markings decide the answer
Pallets are not all the same, and the difference that matters for a garden is how the wood was treated before it shipped. The University of Washington Libraries explains that pallets used in international shipping must meet a standard called ISPM 15, and it states plainly that “Pallets made of raw, untreated wood are not compliant with ISPM 15.” To comply, the wood is either heat treated or fumigated. The same page says “Heat-treated pallets bear the initials HT (or sometimes KD for kiln dried) near the IPPC logo. Pallets treated with methyl bromide bear the initials MB.”
That split is why one pallet can be a reasonable choice and another a poor one. The Ask Extension answer from the University of Maryland Extension Home and Garden Information Center opens with a caution: “Pallets have become a popular choice for garden construction because they are inexpensive and readily available, but exercise caution before using wood pallets in a garden.” It then adds that “Understanding the stamps and markings on a pallet helps in making an educated choice.”
A stamp is evidence about the wood’s history, and the history is not otherwise visible. The UW page notes that “color is not a reliable indicator, especially with older wood.” It also says that “many pre-2010 pallets are still around” and are “likely to be the ones nearing the end of their useful lives as pallets.” That is the reason a pallet that looks clean and unpainted can still carry a methyl bromide treatment. The UW author concludes that “it’s wise not to use wooden pallets for growing food.”
The food-safety concern is strongest for vegetables, but the methyl bromide concern is about the chemical itself. The Ask Extension answer says “This pesticide has been linked to human health problems and ozone depletion.” It recommends that MB pallets be taken to a hazardous waste facility: “Dispose of them at a hazardous waste facility.” So an MB pallet is not a candidate for a flower box either, even if the flowers are not eaten.
Reading the markings: a working table
Use this table as a sorting step. It draws only on the markings described in the UW and Ask Extension pages, and it does not add any treatment the sources do not name.
| Marking | What the source says | Practical use for a planter box |
|---|---|---|
| HT | Heat treated. Ask Extension lists HT under pallets it calls safe, and describes heating to a minimum core temperature of 56°C (132°F) for softwoods and 60°C (140°F) for hardwoods, for a minimum of 30 minutes. | Acceptable by the source’s own heading. |
| KD | Kiln dried. Moisture is “reduced to a level below 19%,” which “helps control warping and some fungal problems.” Ask Extension also says the kilns “do not necessarily reach the same temperatures” as HT wood. | Acceptable, but it is not the same process as HT. |
| DB | Debarked. Ask Extension says the bark was cut off with a scraping tool and that this “has no effect on the wood of the pallet.” | Listed under the safe heading, but DB alone describes bark removal only. |
| MB | Methyl bromide treated. | Do not use. Ask Extension says to dispose of it at a hazardous waste facility. |
| Unmarked | No origin or treatment information. | Reject for food plants when origin and treatment are unknown. |
Notice that the table gives a rule rather than a score. A pallet either carries a treatment the sources accept, or it does not. The sources do not rank HT against KD for planter boxes, and the KD row says the two processes differ.
Two more checks help. Look for the country of origin, which Ask Extension lists as the first identifier. Then look for the inspector code if one is present. The sources do not say what an inspector code proves, so treat it as a sign of inspection, not as a guarantee about the wood.
Wood treatments for the box itself
A planter box built from pallet boards is not automatically a safe box, because the boards may be older, mixed, or partly damaged. Many builders also choose new lumber, so the treatment question moves from the pallet to whatever lumber you buy.
The University of Maryland Extension page on building raised beds gives three options that apply to any wooden planter box. First, “Paint the wood with exterior latex paint to minimize soil contact with treated wood.” Second, use a decay-resistant wood, such as “cedar, black cherry, oak” and similar species. Third, “Apply a heavy plastic liner between the treated wood frame and your garden soil, allowing for soil drainage.” The same page says “Avoid using older types of wood treatments such as CCA, creosote, and Penta-treated lumber.”
Modern pressure-treated lumber is a different case. The page says “Micronized Copper Azole (MCA) is currently the most widely available type of wood preservative for residential use.” It adds that MCA “does not contain arsenic, but it does contain copper.” It also reports research from Oregon State University: “pressure-treated lumber does increase soil copper concentrations by a minor amount, but only within 1 inch of the raised-bed edge.” The Oregon State Ask Expert answer makes a related point about older lumber: “If you are shopping for treated lumber nowadays, I don’t think you’ll find CCA-treated material in the home centers anyway since its use was restricted by the EPA in 2004.”
So a box built from new pressure-treated lumber and lined on the inside is a different project from a box built from unknown pallets. Keep the pallet question and the lumber question separate when you plan the build.
Size the box from the board height
Once the wood question is settled, the box’s shape is simple arithmetic. The Iowa State guide gives a common height and explains where it comes from: “11 inches is a common height as it’s the height of two 2×6 boards (the actual dimensions of a 2×6 board are 1.5 x 5.5 inches).” That gives a formula you can apply to any board whose actual width you measure:
Height = number of boards stacked x 5.5 inches
The 5.5 figure is the actual width of a 2×6 board from the Iowa State note, not the nominal size printed on the label. Pallet boards vary, so measure the actual board before you cut. The table below uses 5.5 inches throughout.
| Boards stacked | Calculated height (inches) | Within the 6 to 20 inch range? |
|---|---|---|
| 1 | 5.5 | No, below 6 inches |
| 2 | 11 | Yes |
| 3 | 16.5 | Yes |
| 4 | 22 | No, above 20 inches |
Iowa State says “Heights typically range from 6 inches to 20 or more inches,” so a two- or three-board box falls within the usual range. Four boards exceed that range, which may still work, but the same source says “Generally, higher heights will be easier for the gardener to work in but require more soil to fill them.” The formula above is simple arithmetic from the Iowa State dimension. None of the sources we opened gives a planter-box height rule of its own.
Width matters for reach. Iowa State says “Beds accessible on both sides can be 3 to 4 feet wide.” A narrower box is easier to reach across if it sits against a wall or fence, where you can reach only from one side. Length is up to you, but a long box with no center support can bow once it is filled with wet soil. The pages we opened do not give a maximum length or a bracing method, so treat those choices as judgment calls to check against the box you are building.
Drainage and the liner
Drainage is where many planter boxes fail. Iowa State is direct about the benefit: “A properly prepared raised bed increases drainage, thereby promoting plant growth and increasing crop yields.” It also says “Raised bed soils should be light and well-drained.” For soil, the same guide describes one approach: “An excellent soil mix can be prepared by mixing equal parts topsoil, organic matter (well-rotted manure, compost, or peat), and coarse sand.” It gives a second option: “Another option is ~70% topsoil and ~30% compost.” For more on filling a bed once the box is built, see our guide on how to fill raised beds.
For a box built from treated wood or from older pallet boards, the liner is the step that matters most. Iowa State says that treated wood may need its inside lined “with woven geotextile fabrics that allow water to drain through but separate the soil/plant roots from absorbing potentially toxic chemicals.” The UMD page gives the same idea in plainer terms: a heavy plastic liner between the wood and the soil that still allows drainage. A liner that traps water is not the goal. If the box has no open bottom, cut drainage holes in the base, and keep the liner from blocking those holes.
Water that stands in the base of a box keeps the soil wet. The sources tie drainage to plant growth, but they do not name a hole size, so choose holes that let water out without letting soil fall through.
Build steps for a basic box
The steps below follow the order the sources support. They do not cover fasteners, joint methods, or how to take apart a pallet, because none of the pages we opened describe those methods.
- Confirm each pallet. Read the markings and reject any MB or unmarked pallet you plan to use for food plants. Set aside boards with rot or soft spots. The pages we opened do not cover structural strength, so judge those boards by eye and do not use a board you doubt.
- Choose the height. Decide how many boards to stack using the formula above. Iowa State names two 2×6 boards as a common height.
- Choose the width and length. Keep the width within reach. Iowa State gives 3 to 4 feet for beds reached from both sides. If the box sits against a wall or fence and you reach from one side only, the same guide says the maximum width should be 1 1/2 to 2 feet.
- Prepare the wood. If the boards are treated or uncertain, paint the outside with exterior latex paint, as the UMD page suggests, and decide on the inside liner before you fill the box.
- Assemble the frame. Use whatever method you are comfortable with. The pages we opened do not recommend a particular method.
- Set the drainage. Place the box on ground or a surface that lets water leave, and add drainage holes in the base if the box has no open bottom.
- Line the inside if the wood is treated or of unknown treatment. Use a material that drains.
- Fill with a light, well-drained mix. Use the Iowa State soil guidance above.
Each step depends on the one before it. Stop at step 1 if the stamp is missing and the box will hold food plants.
Common mistakes
Trusting color. The UW page says color is not reliable, especially on older wood. A pallet that looks clean may still be MB treated, so the stamp is the check.
Skipping the liner for treated wood. Iowa State says the inside may need a liner for treated wood, and the UMD page gives the same advice. Using the box for flowers does not change the chemistry of the wood.
Building a box taller than the soil budget allows. Iowa State says higher beds need more soil. A four-board box is possible, but it costs more soil and asks more of the frame.
Using old CCA-treated lumber. The UMD page says to avoid CCA, creosote, and Penta-treated lumber, and the Oregon State answer says CCA was restricted for residential use in 2004. Check the age and the label of any treated lumber you find in a salvage yard.
Ignoring drainage. A box without drainage holds water in the base, and the Iowa State guide ties drainage to healthy plant growth.
Assuming a stamp means the wood is clean. A stamp is evidence about treatment, not a test of the wood. The sources do not say that a stamped pallet is free of all contamination.
When a pallet box is the wrong choice
A pallet box is not the right answer if you cannot read the stamp, if the pallets are unknown and the box will hold edible plants, or if you need a box that will last many seasons with little maintenance. In those cases the sources point toward known-treatment lumber, paint or a liner, or a non-wood material. The UMD page names stone, concrete blocks, bricks, and synthetic lumber as alternatives. The pages we opened do not compare the costs or lifespans of those materials, so the choice depends on your budget and your site.
How we chose
This guide answers one question: how to decide whether a pallet is suitable for a planter box, and what a basic box needs. We opened pages from university extension services and one university library. We selected pages that address pallet treatment markings, treated lumber in raised beds, and raised bed dimensions. We excluded general blogs and product sellers, because the question is about safety and build geometry, not about buying a product.
We did not rank the sources against one another by popularity, and we did not use any Wikipedia page for a safety or procedure claim. Where a number comes from simple arithmetic, the text says so. The height table uses the Iowa State dimension and multiplication only.
What we could not verify
The pages we opened do not give fastener types, joint methods, or a maximum length for a planter box. They do not give the service life of a pallet-built box, and they do not compare pallet boards with purchased lumber on cost. We could not confirm how long any particular pallet has been in service, and none of the sources describes a test of a box built from pallets.
We also could not confirm anything about a specific pallet supplier, and this guide names none. If a stamp is unclear, the sources say to reject the pallet for food gardens, and we did not find a source that says otherwise.
This guide makes no product recommendations. For a planter that is not built from pallets, see our guide on planter boxes for a deck railing.
FAQ
Are pallets safe for growing vegetables?
Some are and some are not. The University of Washington page and the Ask Extension answer both say the stamp decides it. HT, DB and KD markings are the ones the Ask Extension answer lists as safe for vegetable gardens. MB-treated pallets should not be used, and unmarked pallets should be rejected when origin and treatment are unknown.
What does the HT stamp on a pallet mean?
The UW page says “Heat-treated pallets bear the initials HT (or sometimes KD for kiln dried) near the IPPC logo.” The Ask Extension answer describes HT as heating the pallet to a minimum core temperature of 56°C (132°F) for softwoods and 60°C (140°F) for hardwoods, for a minimum of 30 minutes in a kiln.
How tall should a pallet planter box be?
Iowa State says heights “typically range from 6 inches to 20 or more inches,” and that 11 inches is common because it equals two 2×6 boards. Two or three stacked boards fall in that range. Four boards go above it, which is possible but needs more soil.
Do I need a liner inside a planter box made from treated wood?
Iowa State says the inside of a treated-wood bed may need a liner, and the UMD page recommends a heavy plastic liner that still allows drainage. If the treatment of the wood is unknown, the sources point toward lining it.
Can I use older pallets if they look clean?
The UW page says color “is not a reliable indicator, especially with older wood,” and it notes that many pre-2010 pallets may carry methyl bromide treatments. A clean look does not replace reading the stamp. If the stamp is missing, the sources say to reject the pallet for food gardens.
Bottom line
Read the stamp first, and reject MB-treated or unmarked pallets for any food plant. Then size the box from board height, using about 5.5 inches for each stacked 2×6, and line any treated wood so the soil drains. If you cannot read the marking, choose a different material.
Sources
- University of Washington Libraries, “safety of wooden pallets for vegetable gardens”: ISPM 15 compliance, HT and MB markings, color is not reliable, and the advice not to use pallets for food.
- University of Maryland Extension via Ask Extension, “Planting in Pallets” (#899120): stamp identifiers, HT, DB and KD listed as safe, MB as unsuitable with disposal, and reject unmarked pallets when origin is unknown.
- University of Maryland Extension, “The Safety of Materials Used for Building Raised Beds”: paint or liners for treated wood, avoiding CCA and creosote, and MCA as the common residential preservative.
- Oregon State University Extension, “Raised bed lumber, pressure treated safe?”: the 2004 CCA restriction and the copper research context.
- Iowa State University Extension and Outreach, “Creating Raised Bed Planters”: heights, the 2×6 dimension, bed width, drainage, soil mix, and the liner for treated wood.
