About 18.83 litres, the large format. It's the volume needed for plants that produce for a long time and drink a lot: an indeterminate tomato carried through to frost, a winter squash, a large eggplant, an artichoke, or several lettuce plants at once. Under a 120 × 120 cm grow tent, four of these pots fill the space completely.

The 5-gallon's party trick is potatoes. Roll the pot's walls down to start, put in 15 cm of medium, set the seed potatoes on it, cover. Then, as the stem climbs, unroll the walls a notch and add medium, always leaving the foliage showing. The buried stem produces new stolons at each level, and harvest is a matter of simply tipping the pot onto a tarp. No fork through a tuber, which is more or less impossible to avoid in the garden.

Why fabric rather than plastic: the root that reaches a plastic wall starts to turn and ends up forming a knot where it strangles itself. In a fabric pot it meets air, dries at the tip and stops lengthening. That's air pruning: the plant branches further back and develops a dense mass of fine rootlets instead of a few long coiled roots. Fabric also breathes, so the medium doesn't overheat, and excess water passes through the wall instead of standing.

The trade-off: it dries fast, and at this volume the plant is large and drinks all the more. An indeterminate tomato in a 5-gallon pot in August can need daily watering. Mulching the surface changes a great deal.

• Capacity: 5 gallons, about 18.83 litres.
• Made of non-woven fabric. Built-in handles.
• Promotes air pruning and an aerobic root environment.
• Easier, healthier transplanting, with no root knot.
• Roll-down walls: ideal for growing potatoes by progressive hilling.
• Folds flat for off-season storage.
• Suited for: indeterminate tomatoes, squash, eggplants, artichokes, potatoes.