Large round Corten steel pots for an olive or another tree

We call a pot large when it measures at least 800 mm across the opening. Three of our round models reach that size, all in 2 mm Corten steel: Callisto, a straight cylinder, from 800 to 1400 mm; Clio, a tapered pot with no rim, whose size reads top then bottom (800/600 means 800 mm at the top and 600 mm at the base), up to 1000 mm; and Calypso, a conical pot with a rim, up to 1000 mm. Each one comes 400, 600, 800 or 1000 mm high.

The soil volume is worked out from the outside dimensions, so it is a maximum: take off the drainage layer and the gap you leave below the rim for watering. For Calypso, whose narrower base is not given, we quote the volume of a cylinder of the same diameter, which the pot does not reach. Prices are UK prices in the base finish, our signature patina.

Choose the diameter for the plant it will become, not for the root ball you take home from the nursery. Repotting out of a 1000 mm pot means lifting several hundred kilos of soil and roots, so it pays to size up from the start. The figures below are a guide only: check the needs of a particular species with your nursery.

Height matters as much as width. A tree anchors itself better and stands up to the wind better in 800 to 1000 mm of soil; the 400 mm formats suit shallow-rooted shrubs and wide, low plantings. For bamboo, pick a clump-forming variety rather than a running one.

• Ø 800 mm, 600 to 800 mm high (300 to 400 L): a young olive, a citrus, a Japanese maple, tall ornamental grasses.
• Ø 1000 mm, 800 to 1000 mm high (500 to 785 L): an established olive, a more mature maple, a small multi-stemmed tree, a clump of bamboo.
• Ø 1200 to 1400 mm (up to 1540 L): a tree that is meant to stay put for years, or a specimen underplanted with ground cover.

Empty, a large pot weighs from 22.9 kg (Clio 800/700 × 400 mm) to 96.7 kg (Callisto 1400 × 1000 mm); it is the soil that changes everything. Depending on the mix and how wet it is, moist compost weighs roughly 1 to 1.8 kg per litre, and your soil supplier can give you the exact figure. A planted Callisto 1000 × 800 mm therefore weighs well over half a tonne, and a 1400 × 1000 mm comes to roughly 1.6 to 2.9 tonnes, pot included. On a balcony, a roof terrace or a suspended floor, have a structural engineer or builder check the load before you order.

Set the pot down empty and level, and only fill it once it is in its final spot: once planted, it will not be moved by hand again. Check the route to the garden in advance, as a 1200 or 1400 mm pot will not go through an ordinary front door, and in a terraced house the hallway is often the narrowest point. For a citrus that comes indoors for the winter, choose a smaller size or a wheeled plant caddy rated for the load.

Before filling, find out where the water will leave the base: without a free outlet, hundreds of litres of soil stay waterlogged and the roots suffocate, which matters all the more in a wet British winter. Our product pages do not describe the base of every format, so ask us before you plant, and do not drill the steel without checking with us first. Our guide on how to choose a Corten steel planter covers the other points to settle before you buy.

A 2 mm steel wall does not insulate: in winter, the mass of soil is what protects the roots, and the wider the pot, the longer the heart of the root ball stays frost-free. In colder parts of the country, choose hardy species, line the inside of the wall with a damp-tolerant insulation before you fill, and mulch the surface.

Every pot arrives with the signature Cortenys patina, applied in our workshop. A large pot takes a lot of water, and the excess that runs down the outside carries oxide with it: plan a bed of gravel, dark paving or pot feet around and under it so that the water can drain away. Our Corten care and rust stain guide explains how to deal with a mark.

The protective varnish offered as an option on Callisto, Clio and Calypso greatly reduces this run-off but does not rule it out: even varnished, a Corten steel pot can still mark the paving or patio beneath it, so protect the ground in every case. On the large formats it adds a little to the price, for example £1,440 instead of £1,340 for Callisto 1000 × 800 mm.

For a medium-sized plant or a pair of pots by the front door, diameters of 350 to 600 mm are enough: see our full range of round Corten steel planters.

If your space calls for a rectangular or square shape rather than a round one, our large Corten steel planters page covers the big boxes: troughs up to 2000 mm long and squares such as Cybèle 2 mm, up to 1400 × 1400 mm. To ring a tree planted in open ground with steel, see our bottomless Corten steel planters. Near the sea, our aluminium planters are the better choice, as our guide to Corten steel near the sea explains.