Prefers growing in shallow water or in a very moist loamy soil. Requires a sunny position. Prefers a pH in the range 5.5 to 7.5. Plants are hardy to about -25°c. The sweet flag has a long history of use as a medicinal and culinary plant. It has been cultivated for this purpose but was more commonly allowed to naturalize and was then harvested from the wild. The plant seldom flowers or sets seed in Britain and never does so unless it is growing in water. It can spread quite freely at the roots however and soon becomes established.

The rhizome is candied and made into a sweetmeat. It can be peeled and washed to remove the bitterness and then eaten raw like a fruit. It makes a palatable vegetable when roasted and can also be used as a flavoring. Rich in starch, the root contains about 1% of an essential oil that is used as a food flavoring. The root also contains a bitter glycoside. Some caution is advised, see the notes above on toxicity. The dried and powdered rhizome has a spicy flavor and is used as a substitute for ginger, cinnamon and nutmeg. A pinch of the powdered rhizome is used as a flovouring in tea. The young and tender inflorescence is often eaten by children for its sweetness. Young leaves - cooked. The fresh leaves contain 0.078% oxalic acid. The leaves can be used to flavor custards in the same way as vanilla pods. The inner portion of young stems is eaten raw. It makes a very palatable salad.

Seed - best sown in a cold frame as soon as it is ripe. Stand the pot in about 3cm of water. Pot up young seedlings as soon as they are large enough to handle, keep them wet by standing the pots in shallow water and overwinter for the first year in a greenhouse or cold frame. Seed is rarely produced in Britain. Division in spring just before growth starts. Very easy, it can be carried out successfully at any time in the growing season and can be planted direct into its permanent positions.

Found in moist soils and shallow water in ditches, marshes, river edges and ponds.