About 11.36 litres, the do-everything size of the container garden. It's the serious minimum volume for a determinate tomato like Roma or Tiny Tim, and it's the right size for a trellised cucumber, a compact zucchini, a cabbage, a broccoli plant, or a good clump of perennial herbs. If you were to own only one size of fabric pot, this would probably be it.

Why fabric rather than plastic: in a plastic pot the root hits the wall and starts to turn, over time forming a knot where the roots end up strangling one another. In a fabric pot the root meets air at the wall, dries at its tip and stops lengthening. That's air pruning, and the plant answers by branching further back: you get a dense mass of fine rootlets rather than a few long coiled roots. At equal volume, the plant makes better use of its medium, and transplanting happens without shock.

Two other advantages: fabric breathes, the medium doesn't cook in July sun, and excess water passes through the wall instead of stagnating. Root rot from over-watering — the number one problem of container growing — practically disappears.

The trade-off: it dries faster. A tomato in a 3-gallon pot in full August sun drinks a lot, and repeated drying triggers blossom-end rot, the famous black bottom. Mulch the surface and water regularly rather than heavily.

• Capacity: 3 gallons, about 11.36 litres.
• Made of non-woven fabric. Built-in handles.
• Promotes air pruning and an aerobic root environment.
• Easier, healthier transplanting, with no root knot.
• Folds flat for off-season storage.
• Suited for: determinate tomatoes, trellised cucumbers, compact zucchini, cabbages, perennial herbs.