Pontederia cordata, Pickerel Weed is a vigourous aquatic marginal with upright blue flowers and attractive glossy arrowhead-shaped foliage. It forms large stands, spreading by rhizomatous growth from the boggy water's edge to about 30cm below the surface. Thought should be given to the particular location where it will be planted and whether or not it should be grown in a submerged container to restrict its growth. As always - and particularly with aquatic plants - care should be taken to ensure it does not escape the garden and become naturalised in the surrounding countryside where it can potentially invade streams and waterways. Despite these important common-sense caveats, Pontedaria cordata is an attractive water marginal with its distinctive blue flowers and lush, near-vertical foliage and creates an impressive pondside colony.