Materials
Metal Raised Garden Beds
Metal raised beds are coated steel panels bolted into a frame. They outlast most wood, often 15 to 20 years or more, go together in about an hour, and are safe for vegetables when made from new galvanized or aluzinc steel.
Raised Gardening Beds is owned by the team behind Thrive Garden, which sells some of the products linked on this page.
| Steel type | Coating | Rust resistance | Notes |
|---|---|---|---|
| Galvanized | Zinc | Good | Silver finish that dulls to matte gray |
| Aluzinc (Galvalume) | Aluminum-zinc alloy | Very good | Usually outlasts plain zinc in wet climates |
| Powder-coated | Paint layer over galvanized or aluzinc | Very good while intact | Colors; chips need touch-up |
| Weathering (Corten) steel | Protective rust layer | Fair to good | Rust-brown look; can stain patios |
Steel, galvanized and aluzinc beds
Bare steel would rust through in a few seasons, so every metal bed relies on a coating.
Galvanized steel is coated in zinc. The zinc corrodes first and protects the steel underneath, even at small scratches. It's the classic stock-tank look. Our galvanized raised bed guide covers the coating and its safety in detail.
Aluzinc, often sold as Galvalume, uses a coating of about 55% aluminum and 43% zinc, plus a little silicon. The aluminum adds a barrier layer, so it generally holds up longer than plain zinc, especially in rainy or coastal areas.
Powder-coated beds add a baked-on paint layer over one of those coatings. You get colors like sage green, cream or black, and the paint adds another barrier, but chips should be dabbed with touch-up paint.
Most bed panels are corrugated or ribbed. The ridges stiffen thin sheet metal so it doesn't bow outward under the weight of wet soil.
Do metal beds get too hot?
Metal walls do get hot to the touch in full afternoon sun. In a filled bed, though, the soil only a few inches in from the wall stays close to the temperature of the rest of the bed, because a large mass of moist soil buffers the change.
To keep heat in check:
- Fill the bed fully so soil sits right up against the panels.
- Choose light colors in hot climates; dark powder coat absorbs more sun.
- Mulch the surface 2 to 3 in deep and keep the soil evenly moist.
- Leave about 6 in between the wall and heat-sensitive crops like lettuce.
In cool climates, the extra warmth is a plus. Beds warm up earlier in spring, which helps tomatoes and peppers get going. For a side-by-side look at how wood and fabric compare on heat, see metal vs wood raised beds.
Are metal beds safe for vegetables?
New beds made from galvanized, aluzinc or powder-coated steel are widely used for food crops. Zinc is a plant micronutrient, and the small amount that moves into soil from the coating is not considered a meaningful risk in normal garden soil.
Two cautions. Keep soil pH near neutral (6.0 to 7.0, which most vegetables prefer anyway), because very acidic soil dissolves zinc faster. And skip salvaged metal of unknown history, such as old roofing or painted tanks, which may carry lead-based paint.
How long metal beds last
A new galvanized or aluzinc bed typically lasts 15 to 20 years or more. Aluzinc and powder-coated beds tend toward the longer end. What shortens life:
- Thin panels that flex and crack their coating.
- Standing water at the base, from low ground or heavy clay.
- Deep scratches from shovels or a careless install.
- Salt from coastal air or road spray.
Unlike wood, metal doesn't slowly soften. It usually looks much the same for a decade, then shows rust spots at cut edges or bolt holes first.
Assembling a metal bed
Most metal beds arrive flat-packed as panels, corner pieces, bolts and nuts. One person can put a 4x8 together in 30 to 90 minutes with a nut driver or wrench.
- Wear gloves. Cut panel edges can be sharp, even on beds with rolled top edges.
- Build it in place. A filled bed can't be moved, and an empty one is easy to bend.
- Level the site. Rake the ground flat and remove sod, or lay cardboard over grass.
- Bolt loosely first. Hand-tighten every bolt, square the frame by measuring both diagonals until they match, then tighten fully.
- Fit the braces. Beds over 6 ft long or taller than 17 in need cross ties or center braces to stop the long sides bulging.
- Fill in stages. Add soil a third at a time and check that the sides stay straight.
Kits vary a lot in how they go together; our guide to raised garden bed kits covers what to look for before you buy.
Metal bed sizes and heights
Common footprints are 2x4, 3x6, 4x4 and 4x8 ft, plus round and oval shapes. Keep beds no wider than 4 ft if you can reach from both sides, or 2 to 3 ft against a fence.
Heights usually fall in three groups:
- 11 to 12 in: fine over loosened ground for most vegetables, and the cheapest to fill.
- 17 in: a popular middle height with less bending and room for carrots.
- 24 to 32 in: easy on the back and good over hard ground, but a 4x8 bed 32 in tall holds over 80 cu ft of soil. Many gardeners fill the bottom third with logs or branches to cut that down.
For help weighing height, size and material together, see our guide to the best raised garden beds. One option if you want a ready-made metal bed is Thrive Garden's galvanized metal raised garden beds.
How to choose
Pick aluzinc or coated steel if
You live somewhere rainy, humid or near the coast, or you want a bed that may last 20 years.
Galvanized is fine if
Your climate is moderate and you like the plain silver look. It costs a little less than aluzinc.
Choose a light color if
Your summers are long and hot. Light finishes absorb less sun than dark green or black.
Go taller with care
Beds over 17 in need braces and a lot of soil. Plan how you will fill them before buying.
Related guides
- Zinc coatings and food safety
- Steel, cedar or fabric: a head-to-head
- What to check before buying a kit
- How to pick the right bed for your yard
- Soil depth by crop
Do metal raised beds rust?
Coated steel beds do eventually rust, but slowly. Expect the first spots at cut edges and bolt holes after many years. A dab of zinc-rich paint on bare spots slows it down.
Do you need to line a metal raised bed?
No. Most gardeners simply fill it. In very hot climates, some tuck a band of cardboard or landscape fabric against the walls to soften the heat. Leave the bottom open so the bed drains.
Can metal beds go on a patio or concrete?
Yes, as long as water can drain out at the base. Use a deeper bed, 18 to 24 in, since roots can't go into the ground below. Expect some water staining on the surface around the bed.
Ready to buy a raised bed?
Thrive Garden sells galvanized metal raised beds and fabric beds in several sizes.
Raised Gardening Beds is owned by the team behind Thrive Garden, which sells some of the products linked on this page. Read our disclosure.