One of the most successful plants in my bog garden is yellow flag, a rhizomatous, beardless iris. It’s long narrow sword-like leaves give a strong vertical accent to the garden and the bright yellow flowers in provide a splash of color in mid-spring. Yellow flag thrives in wet lands but also does well in a border with moist soils where it is less vigorous and, therefore, less likely to become invasive. It spreads by seeds and rhizomes and can form large dense colonies that are difficult to remove once established. Yellow flag has been used in sewage treatment because it can remove heavy metals from the soil. Historically, preparations from the roots have been used as snuff, the flowers for dye, and the rhizomes as a laxative. The flowers are lovely in bouquets and were probably the model for the fleur de lis, the heraldic emblem of French kings in the 12th century.
Type: Herbaceous perennial
Bloom: Yellow to cream flowers 3-4” across in mid-spring
Foliage: Long, narrow, sword-like leaves
Size: 3-5’ H x 2-3’ W
Light: Full sun to partial shade
Soil: Rich, wet to moist
Hardiness: Zones 4-9
Care: Control size if plant becomes invasive
Pests and Diseases: None of significance
Propagation: Seed, division in late summer to fall
Companion plants: Bog plants such as Venus fly trap, pitcher plant, sundew.
‘Berlin Tiger’ (yellow flowers with brown veining)
‘Crème de la Crème’ (white flowers)
variegate (variegated foliage)