Optimum Planting Time: September – November
Flowers: February - March
Height: Up to 90cm for taller varieties, 10-15cm for dwarf varieties
Where to plant
Iris germanica, better known as bearded or border irises, flower in summer and do best in full sun, as do the tall Dutch irises (Iris hollandica). The dwarf irises (Iris reticulata and Iris histrioides) flower in early spring and will grow in sun or partial shade. All irises prefer a well-drained soil.
How to plant in the ground
1. If planting on heavy soil, dig in compost and horticultural grit to improve drainage.
2. Plant Dutch irises and dwarf irises approximately 7cm deep, using a bulb planter or trowel to dig the holes. Space the bulbs 10cm apart.
3. Bearded irises should be planted shallowly, laid flat so that the upper surface of the rhizome is partially exposed and can be baked by the summer sun. Space bearded irises 30cm apart.
4. Water after planting.
How to plant dwarf iris in containers
Dwarf irises are ideal for planting in containers for a burst of early spring colour. They also work well as the top layer of a bulb lasagne, with layers of later-flowering bulbs like daffodils or tulips planted below them. Dutch irises can also be grown in large containers for beautiful summer displays.
1. Water irises during long periods of dry weather but take care not to overwater them.
2. Mulch with well-rotted farmyard manure in spring, but don’t cover exposed rhizomes with mulch as this could cause them to rot.
3. Deadhead flowerstems once the flowers have finished, cutting down to the base of the stem. Leave the foliage of dwarf and Dutch irises to die back naturally before removing it. Remove any yellowed or damaged leaves from bearded irises.
Pests and Diseases
Irises can be prone to various fungal, bacterial and viral diseases. Leaf spot appears as brown spots on leaves and can cause the entire leaf to eventually wither. Ink disease affects mainly the bulbous irises, causing black blotches on leaves and on the bulbs themselves. Rust (small orange-brown pustules on leaves) can affect both rhizomatous and bulbous irises, in severe cases causing leaves to wither. Both bulbs and rhizomes can also be affected by rot.
Removing all dead or damaged leaves at the end of each year can reduce the spread of leaf spot and rust. Bulbs affected by ink disease should also be disposed of. Fungicides approved for the control of rust on ornamental plants may provide some control of the disease on irises too. Avoid spraying fungicides on irises planted near water, as the spray is likely to harm wildlife.