Short answer: pallets stamped HT (heat-treated) are the safe choice for a raised bed. Never use a pallet stamped MB (methyl bromide fumigant), and skip any pallet that's stained, oily, smells of chemicals, or came from an unknown source. Line the inside walls with plastic if you're unsure of the wood's history. Build the bed no wider than 4 ft (1.2 m) if you can reach in from both sides, 3 ft (0.9 m) against a wall, and 6–12 in (15–30 cm) deep. Expect pallet wood to last only a few seasons in damp soil.
How to read a pallet stamp
Pallets used in international shipping must be treated against wood pests under the IPPC standard ISPM 15. The treated wood carries a stamp with the IPPC wheat-ear symbol and these codes:
| Mark | Means | For a garden bed |
|---|---|---|
| HT | Heat-treated: the core of the wood held at 56 °C (133 °F) for at least 30 minutes | Good choice |
| MB | Fumigated with methyl bromide, a highly toxic pesticide | Never use, never burn |
| KD | Kiln-dried (often shown with HT) | Fine |
| DB | Debarked | Fine; tells you nothing about chemicals |
| Two-letter code | Country where it was treated (US, CA, DE…) | For information only |
| Number | The certified treatment facility | For information only |
Penn State Extension's advice on MB is blunt: don't use these pallets for any home project, and don't burn them. Methyl bromide is being phased out and MB pallets are uncommon today, but they still turn up.
Unstamped pallets are usually domestic and were never chemically treated. The catch is what they carried. A pallet that spent its life under feed sacks is fine; one that sat under drums of solvent or pesticide is not. University of Illinois Extension lists chemically treated pallet wood alongside creosote ties as materials to keep out of food beds. If you can't learn a pallet's history, don't use it for vegetables.
A quick pallet checklist
- Clean, dry and with no smell.
- No dark stains, oily patches or spill marks.
- No paint. Painted pallets are color-coded pool stock, and the paint is unknown.
- Stamped HT, or unstamped from a source you know, such as a feed store or lumber yard.
- Solid boards without rot, mold or heavy splitting.
Other salvaged wood to keep out of food beds
- Old pressure-treated lumber. Anything treated before 2004 is likely arsenic-based CCA.
- Railroad ties and old utility poles, treated with creosote or other heavy-duty preservatives.
- Painted barn boards and trim. Paint from before the 1978 U.S. ban on lead paint in homes may contain lead. Test it or leave it out.
- Composite and particleboard, which swell and fall apart in wet soil.
Taking pallets apart
Pallet nails are usually spiral or ring-shank, designed not to pull out. Prying boards off splits a lot of them. Two faster methods:
- Cut them free. Run a reciprocating saw with a metal-cutting blade between the deck board and the stringer to shear the nails.
- Keep whole sections. Saw along the inside of the stringers and use the boards still nailed to their 2×4 blocks as ready-made wall panels.
Wear gloves and eye protection, pull or clinch every protruding nail, and don't jump on pallets to break them. Penn State notes that block pallets can weigh over 50 lb (23 kg).
Liners: when and how
A liner keeps soil and its moisture away from the wood. It reduces any leaching worry and adds a season or two of life.
- Staple heavy polyethylene sheet (6 mil / 0.15 mm) to the inside walls only.
- Leave the bottom open so the bed drains. Illinois Extension advises removing any plastic used to smother weeds before you fill the bed, so it doesn't block drainage.
- Landscape fabric is not a chemical barrier. It passes water, so it only keeps soil from sifting through gaps.
- Cardboard or newspaper on the ground under the bed smothers grass and breaks down by itself.
Sizing a raised bed
| Dimension | Recommendation |
|---|---|
| Width, reachable from both sides | Up to 4 ft (1.2 m) |
| Width, against a wall or fence | Up to 3 ft (0.9 m) |
| Depth of soil | At least 6–12 in (15–30 cm); 12 in for carrots and potatoes |
| Length | As long as you like; standard pallet boards are 40 or 48 in (1.0 or 1.2 m), so plan in those steps |
| Height needing extra bracing | Over 18–24 in (45–60 cm) |
| Paths | 18–24 in (45–60 cm) for a home garden; about 4 ft (1.2 m) for wheelbarrows, mowers or wheelchair access |
A 4 × 8 ft (1.2 × 2.4 m) bed filled 12 in deep holds 32 cu ft of soil, about 1.2 cubic yards (0.9 m³). That's a small truckload, so price it before you build. Illinois Extension's example fill is about 60% topsoil, 30% compost and 10% soilless mix. Run long beds east to west for even light.
Make it last longer
- Pallet wood is mixed species, mostly non-durable, so set the bottom board on a gravel strip rather than bare soil.
- Add corner posts of 2×4 or 4×4 inside the walls. Pallet boards are thin and bow under wet soil.
- Brace beds longer than 6 ft (1.8 m) across the middle with a cross tie, or with stakes on the outside.
- Plan to replace the boards in three to five years. If you want a bed that lasts, rebuild it in cedar or ground-contact treated lumber.
To stretch the season at either end, a cold frame can sit right on a bed's frame. The convertible Greenhouse-Coldframe works as a vented lid for early greens.
Frequently asked
Are HT pallets safe for growing vegetables?
Heat treatment adds no chemicals, so HT pallets are generally considered fine. The bigger unknown is what was spilled on them in use.
What does MB on a pallet mean?
Methyl bromide fumigation. Don't use the wood for any home project, and don't burn it.
Should I line the bottom of a raised bed?
Not with plastic: it blocks drainage. Use cardboard to smother weeds, or hardware cloth if gophers or voles are a problem.
Guidance drawn from the IPPC ISPM 15 standard and Penn State and University of Illinois Extension. When a pallet's history is unknown, leave it out of the food garden.