Iris Gerald Darby
Notify MeMost iris are bought for the flower. 'Gerald Darby' is worth having for its stems, which push out of the ground in spring a deep purple-black and hold that colour up the flower stalk and into the leaf bases for weeks. The flowers, when they come, are violet-purple with paler falls marked by a yellow flash and dark veining. This is a hybrid of two American blue flag species, Iris x robusta.
Its height and its love of water make it a natural for a pond or stream margin, where it can stand in shallow water or in the wet ground alongside. It also works at the back of a damp border, and in a large container kept permanently moist. The dark spring stems read strongly against fresh green growth.
Give it a position in sun or light shade in humus-rich soil that stays moist to wet, slightly acid rather than limey. It will grow in up to 10 cm of standing water at the edge of a pond, which is unusual among garden iris. The clump thickens steadily and can be divided from midsummer to early autumn. Foliage dies away over winter.
Reaches 1 to 1.8 m in flower, making it one of the tallest iris available.
Trimming: Take the flower stems down after flowering, and cut the foliage back in late autumn once it yellows. Divide congested clumps between midsummer and early autumn, replanting the rhizomes just below the surface.
Deadheading: Not much needed, as the flowers are short lived and drop cleanly. Cutting the whole stem out once the last bud opens keeps the plant looking deliberate.
Fertilising: A general feed as the first shoots show, under a compost mulch, supports the tall stems. Feeding matters most on lighter soil, and less so in silty ground beside water.
Watering: This iris cannot be allowed to dry out. Away from a pond edge it needs deep, frequent watering all the way from September to March, with a heavy mulch to hold moisture at the root.
Pest Control: Slugs and snails are the main problem and hide among the leaf bases in damp ground. Check the crowns in spring. Aphids may cluster on the flowering stems.
Disease Management: Iris leaf spot causes brown patches ringed with yellow, worse in a wet season, and is managed by removing affected leaves and clearing old foliage in autumn. Rust can also appear in humid weather.
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- Urban delivery within mainland New Zealand: $19.95
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