After 13 years as head gardener of England’s world-famous gardens at Sissinghurst Castle, Sarah Cook may have been forgiven for putting her feet up when she retired to the beautiful Suffolk countryside. But instead of twiddling her thumbs, she has been on a 14-year odyssey to rediscover and collect Cedric Morris’s bearded iris. The Suffolk-based artist and plantsman introduced and named around 90 varieties during the 1940s and 50s that caused a stir at Chelsea and have a painterly beauty all their own.
In her idyllic garden, the Cedric Morris blooms have their own patch while in another vast bed there are hundreds of other bearded iris all being carefully watched over. She shared her top five expert tips on how to nurture these elegant and statuesque beauties.
Photography by Clare Coulson.
1. Lighten up your soil.
Irises need to be grown on well-drained soil and tend to flourish in areas with lower rainfall. But if you have heavier soil, all is not lost. Sarah makes her beds slightly mounded to help drainage and also adds some grit. Most important, make sure that the rhizome is at ground level (often you may even see a happy rhizome above the soil). If this part of the plant is submerged and sitting in damp soil in winter, it may rot.
2. Choose good neighbors (or preferably none at all)
Irises do not like competition, which is why they are often grown in a separate beds or up against a sunny wall. They will not flourish in crowded herbaceous borders where neighboring plants will shade the sun. “They won’t flower if they are in a poor position and eventually they will die from the competition,” adds Sarah.
3. Divide every four or five years.
As a plant’s rhizomes multiply and form congested clumps, an iris eventually will stop producing flowers. Carefully dig up the whole plant and break up each chunk of the rhizome. These can then be replanted (each rhizome creates a new plant) and the leaves can then be trimmed back to a neat fan shape. This is best done in July. Some smaller rhizomes may not form new plants in the following year; they may need longer to settle in. For this reason, Sarah advises planting some of the chunkier rhizomes close to some smaller divisions to ensure you always have flowers.
4. Don’t forget to feed.
Irises may be happy on light sun-baked soils, but don’t neglect them. “They are quite hungry. They like being fed,” says Cook, who gives them her own custom mix of Grow More with extra sulphate of potash and some kieserite for extra magnesium (a mix she used on the roses in her time at Sissinghurst) around March and then again in July when they are putting on their root growth. And water in irises that have just been planted or newly established plants if there’s no rain.
5. Keep them tidy.
When a plant has entirely finished flowering, Sarah advises neatly snapping off the entire stem directly from the rhizome—pull the stem forward to make a neat cut that will help prevent rot or virus. If the leaves look unsightly, then cut them back to a short fan and the plant will quickly make new foliage.