23: Spring 2009

Author: Brita Carson

Pacific Coast Irises

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Pacific Coast IrisesBrita Carson

Pacific Coast Irises (PCIs), also called Pacific Coast Native Iris, are spring flowering plants decorating borders in April and May. The species of the series Californicae come from the Pacific coast area of western America which includes the states of Washington, Oregon and California. They make large, splaying clumps often placed near the front of the border because most of them are only between one and two feet high. Intensive breeding by American hybridisers over recent years has given us beautifully coloured standards and falls, all with striking flower patterns. Many of the species are found at the edge of pine forests, high in the mountains, and hybridisers are trying to stretch the boundaries to grow them successfully in areas both to the north and south. The resulting cultivars can cope with maritime climates and with careful positioning a good situation can be found to get the best from these very special flowers. Good news for gardeners in Scotland with mild wet winters.
PCIs are noted for being difficult, sometimes dying after a few years.
The following are their optimum growing conditions:
Sharp drainage in a rich but gravely soil full of grit and stones.
A soil which is neutral to acid (pH between 5 and 7).
They grow best in filtered shade or morning sun.
Suitable positions could be: a sloping sunny bank especially east facing; a raised bed, trough or large shallow pots with lime free soil; a south-west facing rock garden; or south facing site with some midday shading from over-hanging plants; or under hedges either deciduous or evergreen to keep the ground dry so that the rhizome can have a rest period after flowering.
To plant out in spring or autumn is a subject of debate. One thing they don’t like is transplanting so grow from seed for new exciting results.
Seed Germination: Plant seeds in a good, moist potting mix which should be fast draining with a pH of 6.5-7. Plant so that you can separate and easily remove individually. Keep in a cool area at 50° F (10°C). Seed will not germinate at temperatures above 70° F (21°C). No freezing is necessary but give outdoor temperatures for 3 weeks. Germination should take about 2 months. Transplant when the seedlings are 3-6 inches tall. They transplant well as seedlings, but only when actively growing as mature plants. Most hybrid seedlings will bloom in the second spring. Species can sometimes take longer. Seeds have an inhibitor so they won’t all germinate at once.
Irises generally don’t suffer too much from pests and diseases. Cut off old leaves before spring growth starts. Give them an annual application of low nitrogen fertiliser in early spring and enjoy the show that follows. As a special gift, give them the pine needles from the Christmas tree as a mulch.

First published in the Scottish & Northern Borders Group Newsletter, Spring 2007
and subsequently in Cornucopia Issue 23
© Copyright for this article: Brita Carson

This article was taken from a copy of Cornucopia that was published in 2009. You could be reading these articles as they are published to a national audience, by subscribing to Cornucopia.

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