Corten Planters: How to Plant Them and What Survives UK Summer

A corten planter is one of the easiest things in the garden to get wrong, and one of the easiest to get right. It mostly comes down to whether you pick plants that want the same conditions the metal is quietly creating.

We make these planters to order from our Nottingham workshop, and the single question we get more than any other is some version of: what do I actually put in it, and will it survive the next heatwave? The short answer is that quite a lot will, as long as you stop thinking of a corten trough as a container and start thinking of it as a small patch of sun-baked Mediterranean hillside. Once that clicks, the plant choice becomes obvious.

Here's how we'd approach it.

What corten does to a plant's roots

Weathering steel holds heat. On a bright July afternoon, the outer skin of a corten planter in direct sun can sit somewhere between 40 and 50 degrees to the touch. That warmth doesn't penetrate all the way to the centre of the compost — a decently sized planter keeps a cooler core — but the roots nearest the metal do sit in a noticeably warmer zone than they would in a terracotta or timber container.

That's a problem for hydrangeas and ferns and anything else that evolved under a tree canopy. It's a gift for everything that evolved on a Greek hillside or a Spanish rooftop. Lavender, rosemary, olives, agapanthus, salvias, grasses — they don't just tolerate the warmth, they want it. Plants that would sulk in a wet year will perk up when their roots are sitting against a sun-warmed steel wall.

The other thing worth knowing before you plant: for the first twelve months or so, the patina is still settling. Rust runoff is harmless to soil and plants (it's just iron oxide — mildly useful, if anything) but it will mark pale paving. If your planter is sitting on Yorkstone or limestone, put gravel or dark slate under it for the first year. We've had a few customers learn this the slightly expensive way.

If you want the full chemistry of how the patina forms and why it self-heals, our complete corten steel guide goes into it properly.

Getting the planter set up

Drainage matters more than anything else you'll do. Every corten planter we make comes with drainage holes drilled into the base as standard, because there is no faster way to kill a plant in metal than leaving it sitting in a puddle. If you've bought a planter that didn't come pre-drilled, stop and drill four to six holes of roughly 12mm diameter before you do anything else.

We don't bother with a deep layer of crocks — that advice is mostly a hangover from smaller Victorian clay pots. A single layer of gravel or a square of landscape fabric over the drainage holes is enough to keep compost from washing out.

For compost, skip the cheap multi-purpose stuff. It compacts, holds too much water, and runs out of nutrients in weeks. For Mediterranean planting — which is most of what goes into corten — we use a mix of John Innes No. 3 loam-based compost with about 30% horticultural grit stirred through it. That mimics the thin, stony soils these plants actually come from. For general mixed planting you can get away with peat-free multi-purpose cut with around 20% grit or perlite. For ericaceous shrubs (and honestly, very few belong in corten) use ericaceous compost with extra grit and accept you'll be replacing it every three or four years.

A finishing layer of gravel or bark mulch on top, about three centimetres deep, locks moisture in and keeps the surface cool. Skipping this step is probably the single most common reason a planter looks parched by mid-July.

One more thing: if the planter is going into a south- or west-facing position that catches afternoon sun for hours, you can line the sides (not the base) with hessian or a strip of bubble insulation. It takes the edge off the heat for the root ball. For Mediterranean planting it isn't necessary, but for anything borderline — say, an acer in a sheltered courtyard — it makes a real difference.

What actually survives a UK summer

The plants worth putting in a corten planter break down into four or five loose groups, and most good planting schemes combine them rather than sticking to one.

For architectural structure and year-round presence, olive trees are the obvious choice and for good reason — the silver-grey foliage against rusted steel is one of those combinations that always works. Go for a hardy cultivar like 'Arbequina' or 'Cipressino' if you're anywhere north of the Midlands, because the supermarket olive trees tend to be trained on rootstocks that struggle below about minus five. Phormium tenax is our second-favourite structural plant for corten, particularly the bronze and burgundy forms. A clipped bay standard, a dwarf mountain pine (Pinus mugo), or a mature cordyline all do similar work in different styles.

For flowers through summer, lavender is the default and difficult to beat — 'Hidcote' and 'Munstead' are the most reliable English varieties, whereas the French and Spanish forms tend to scorch if we get a hard winter. Agapanthus looks genuinely spectacular planted against corten (the blue-purple heads and the warm rust are complementary in a way that photographs well — if you look at our Instagram, most of the "nice" shots involve one or both). Salvia nemorosa, particularly 'Caradonna', flowers for months and is virtually indestructible. Verbena bonariensis is worth planting for the height and the bees. Echinacea and Rudbeckia give you late-summer colour when everything else is flagging.

Ornamental grasses might be the single best category of plant for corten. The movement offsets the hard metal edges, and none of them are fussy. Stipa tenuissima is the one everybody knows — fine, flowing, almost luminous when the sun catches it. Pennisetum 'Hameln' is compact and gives you those bottlebrush flower heads from August onwards. Calamagrostis 'Karl Foerster' is the tall upright one if you want screening as well as movement. Festuca glauca makes neat blue-grey mounds and fits into smaller troughs where fuller grasses would look wrong.

If the planter is near a kitchen door, plant it with herbs. Rosemary, thyme, sage, oregano and bay all love the conditions, and you'll use them. The one exception is mint — it wants moisture and a bit of shade, and will sulk in a hot planter. Stick mint in a separate pot somewhere cooler.

For very exposed south-facing spots — roof terraces, balconies, anywhere the wind gets at things — succulent planting is honestly hard to beat. Sempervivums are evergreen, hardy, self-propagating and come in dozens of colours and forms. Creeping sedums will spill over the planter edge. Delosperma will flower bright magenta through the hottest weeks.

What wouldn't we plant? Hydrangeas in direct sun, despite how good they look in a gardening magazine shot — they will collapse by eleven most days in July. Ferns (with a couple of tough dryopteris exceptions) don't want the heat. Acers in windy positions get scorched leaves. And bedding annuals that need daily watering are a thankless commitment in a hot planter — a week away from home and they're gone.

Four planting schemes that work

For a modern minimalist look, three identical corten cube planters in a row, each holding a single specimen olive tree underplanted with a cloud of Stipa tenuissima. Nothing else. It sounds almost too simple when written down, but it's the scheme we've installed more times than any other, usually for architects' clients.

For a Mediterranean courtyard feel, a long rectangular trough planted up with lavender at the front, rosemary through the middle, and a clipped bay standard in the centre. Top-dressed with pale gravel. Incredibly low maintenance once established, and it smells wonderful on warm evenings.

For a contemporary prairie look — our personal favourite, if we're honest — mix Calamagrostis 'Karl Foerster' with Echinacea purpurea, Verbena bonariensis, and Sedum 'Autumn Joy'. This works particularly well in wider troughs flanking a patio or a corten steel garden screen, because the vertical line of the grasses echoes the screen behind them. You can see some combinations of this sort in our 15 metal garden screen ideas for UK gardens piece.

For a small balcony or terrace, compact corten bowls with mixed Sempervivum, a single Festuca glauca, and creeping thyme tumbling over the edge. Zero maintenance, evergreen, and tolerant of the worst position the building can put it in.

Getting through the summer

The biggest mistake people make with corten planters is overwatering them. The second biggest is underwatering during heatwaves. These sound contradictory but aren't — the trick is watering deeply and less often, rather than sprinkling a bit every day.

In most UK summers, two or three proper soakings a week will do it — soak until water runs clearly out of the drainage holes, then stop. That kind of watering encourages roots to grow downwards, where the compost is cooler. Daily light watering keeps the roots at the hot surface, where they'll be the first things to stress when the temperature spikes. Water in the early morning or after seven in the evening; midday watering is largely wasted to evaporation.

During a proper heatwave — the kind where it's 28+ for several days running — you may need to water daily, and it's worth moving smaller planters into partial shade if you can. A mulch layer, as mentioned earlier, buys you an enormous amount of forgiveness here.

On feeding: container plants get through their nutrients faster than anything in open ground. A liquid seaweed or tomato feed every two or three weeks from May through August keeps flowering plants going. For structural things like olives and bay, a slow-release granular feed once in April is usually enough for the whole season.

The mistakes we see most

We get emails about sad-looking corten plantings regularly enough that the causes are pretty predictable. Overwatering is top of the list — metal planters look like they'd dry out fast, and some of the smaller ones do, but a larger trough in a shaded position can stay wet for surprisingly long. Check the compost five centimetres down before you water anything.

Planting too densely is the next one. The instinct is to fill the planter so it looks generous on day one, but corten amplifies competition for water, and by August everything is fighting. Leave room.

Choosing plants for looks rather than conditions is the third, and the one we'd most like to stop people doing. A hydrangea in a south-facing corten planter will look beautiful for about two weeks in June and exhausted for the rest of the year. Pick plants that actively want what corten offers, not plants you're trying to force into conditions they'd rather not have.

A few things people ask us

Do corten planters get too hot for plants in summer? The outer surface can hit 40 to 50 degrees in strong sun, but the compost in the middle of any reasonably sized planter stays a lot cooler. Mediterranean and drought-tolerant plants don't notice. For anything more sensitive, use a deeper planter and line the sides with hessian.

How long do they actually last? Quality corten planters made from 2 to 3mm steel will last 25 years outdoors without any painting, sealing or annual treatment. The patina does the protective work.

Will the rust harm my plants or soil? No. It's stable iron oxide and entirely inert once the patina has formed. Trace iron in the runoff is harmless to plants and potentially mildly beneficial to soil. It's only a problem for pale paving underneath during the first year.

Can I grow vegetables in one? Tomatoes, peppers, chillies and courgettes do brilliantly — the warm root zone is a real advantage for fruiting crops. Salad leaves and spinach prefer cooler conditions and are better off in ceramic or wood.

Do they need protecting in winter? The planter itself doesn't — corten is entirely winter-proof. The plants inside might, depending on what you've chosen. Wrapping the outside with hessian during a hard frost reduces root freezing for evergreen planting.

If you're planning something bigger

Most of the planter schemes we're asked to quote for are either a row of matched planters along a boundary, or planters paired with metal garden screens to create a fully coordinated design. We make both to order in any size, and the design team runs a free consultation on every project — there's more about that on our design consultation page, or you can just have a look through the current range of outdoor metal planters and get in touch if you want something modified.

Get the plants right and a corten planter is one of the lowest-maintenance things in the garden. Get them wrong and it's a summer of disappointed watering. The difference is mostly in the first ten minutes of choosing what to put in it.

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Written by the design and installation team at Metal Garden Screen Ltd. We've been making corten steel planters, screens and garden pieces to order from our Nottingham workshop since 2019.