Metal planters: Corten steel or aluminium

To compare like with like, we took from our product pages the sizes offered in both materials. Weights are the empty weights shown on each product page; prices are UK prices in the base finish, our signature patina for Corten and black RAL 9005 for aluminium, which costs the same as its seven other colours. Cybèle, Déméter, Thalie and Iris are made from 3 mm aluminium. For Iris, the size reads long side / equal sides × height.

Weight first. Size for size, the aluminium version is 1.8 to 2.1 times lighter than its Corten steel twin, even though its 3 mm sheet is thicker than the 1.5 or 2 mm of the Corten. Then price: in our UK prices, aluminium costs between 12% and 46% more on Cybèle, Déméter, Thalie and Iris, with the smallest gap on the small Iris (£830 against £740) and the widest on the 800 mm Cybèle (£1,560 against £1,070). Maïa is the exception, at £2,780 in aluminium in both sizes, against £900 and £1,190 in Corten steel.

Finally, the range: across these five designs we offer Corten steel in far more sizes than aluminium, and taller ones.

• Cybèle: 27 sizes in 2 mm Corten and 7 in 1.5 mm, from 400 to 1400 mm square and up to 1000 mm tall; 10 sizes in aluminium, up to 800 mm tall.
• Déméter: 21 sizes in 2 mm Corten, 900 to 2000 mm long and 300 to 600 mm wide, plus 6 in 1.5 mm; in aluminium, 3 lengths (1200, 1500 and 2000 mm), 500 mm wide and 600 mm tall.
• Thalie: 23 sizes in Corten, 3 of them rectangular; 5 square sizes in aluminium, from 600 to 1400 mm.
• Iris and Maïa: the same sizes in both metals, 8 for Iris and 2 for Maïa (see the page for Maïa in aluminium).

Where every kilo counts, aluminium wins. A 6 m run of three Déméter troughs at 2000 × 500 × 600 mm weighs 205.5 kg empty in Corten steel, against 106.5 kg in aluminium. A 400 mm Cybèle drops from 13.7 kg to 7 kg, light enough to move from one corner of the patio to another as the seasons change.

These are empty weights. Filled with compost and watered, a planter weighs far more than its metal. On a balcony or a roof terrace, have a structural engineer or the building's managing agent confirm the permitted load before you install large volumes. Our guide on how to choose a Corten steel planter is a reminder that it is the wet soil, far more than the steel, that weighs.

In the garden, standing on soil or a paving slab, weight works the other way, in favour of Corten: a heavy run of troughs stays put in the wind and does not shift once planted.

The choice starts with the look. Our Corten steel planters arrive with the signature Cortenys patina applied in the workshop, an earth and amber tone that keeps changing with the light and the seasons. There is nothing to paint: the patina is part of the piece.

In aluminium, the colour is stable and yours to choose. Each design comes in eight RAL colours at the same price: white 9016, anthracite grey 7016, black 9005, blue 5001, yellow 1005, green 6018, red 3020 and orange 2004. Black sets off foliage, anthracite matches most modern window frames, and a bright colour turns a planter into the focal point of a courtyard.

As for upkeep, powder-coated aluminium needs nothing more than an occasional clean. Corten steel needs no particular care either; only the surface it stands on calls for some thought, as we explain below.

Untreated Corten steel can leave rust run-off, especially in its first months, on pale paving, limestone or a pool surround. The protective varnish we offer as an option on our five Corten designs greatly reduces these marks without ruling them out: even varnished, a Corten steel planter can still stain the paving. Stand it on spacers, small feet or a bed of gravel; Thalie, on its legs, keeps an air gap under its base. Our Corten steel care guide covers these precautions and how to treat a stain.

Powder-coated aluminium does not rust, so it will not mark light stone. It is the metal we recommend beside a swimming pool and right on the coast, where salt stops the Corten patina from stabilising. Our guide to Corten steel near the sea explains why.

Because every design exists in both metals, you do not have to pick one for the whole garden. A line of Déméter in aluminium along the pool, a pair of Corten Cybèle cubes on the lawn: the shape carries through from one end to the other, and only the material changes with the exposure.

Keep the two metals from touching: where they meet and water can sit, slip a spacer or a gasket between them. And if the roots need to reach the soil below, Rhéa and Gaïa, our bottomless planters, also come in both metals.

Start with where the planter will stand, then look at the budget.

• Balcony, roof terrace, a planter you will move: aluminium, roughly half the weight. Iris in aluminium weighs 5.9 kg in its smallest size.
• Pool surround, seafront garden, very pale paving: aluminium, with no rust run-off.
• A colour to match a front door, a rendered wall or window frames: aluminium, in eight RAL colours.
• Garden, border, lawn, a long run on a budget: Corten steel, cheaper size for size and offered in far more sizes.
• A tall planter, above 800 mm: among these five designs, only Corten steel goes up to 1000 mm (Cybèle, Déméter, Thalie).
• A material that weathers and gains character over time: Corten steel.