How to grow and care for iris flowers

Irises are easy-to-grow perennials with showy flowers in spring and summer. They make great cut flowers and come in any colour combination that suits your fancy. With types that grow in all conditions, from water to dry spots, you’re bound to find one that suits you.

What you need to know about iris

Name: bearded iris, Dutch iris, Japanese iris, Siberian iris, Iris species and varieties

Height: typically 1m, but shorter forms are available

Foliage: evergreen or deciduous

Climate: cold temperate, warm temperate, semi-arid, sub-tropical.

Soil: prefers deep, well-drained soil.

Position: full sun.

Flowering: showy flowers of various colours at the tops of the plant. Flowering time depends on the variety.

Feeding: regular feeding with a balanced, controlled-release fertiliser.

Watering: regular watering for most types. Some need quite wet conditions.

Iris

Appearance and characteristics of iris

The iris has a tuft of sword-like foliage arising from the ground. In many commonly grown varieties, this foliage dies down in winter, and is replaced with fresh leaves in the spring. In other irises, the leaves are evergreen.

The flowers appear on strong stems that arise from the base of the foliage. Usually a sequence of flowers appears on the stems. In some forms, there is only one flower per stem, but many flowers in a season.

Iris flowers have six petals, three that come out vertically or droop, and three that stand up. Blue and purple are common colours, but the colour range of irises is truly amazing, with just about every colour combination imaginable.

Irises generally flower in spring and summer, however there are forms that flower in winter.

There are a number of plants that are referred to as “iris”, and which look very similar, but are not of the Iris genus. These include the wild iris (Dietes); native iris (Patersonia) and New Zealand iris (Lambertia).

Uses for iris

Use irises to bring colour to a mixed garden bed. Some people grow them in a row as a border to a garden. Smaller irises can be grown in containers.

Many are grown for their cut flowers, although the Dutch iris is probably the best for this purpose. Some irises, such as the Louisiana iris, are grown in ponds or bogs.

How to plant iris bulbs

True irises are perennials that have a bulb or rhizome. These can be purchased in pots, but are often sold in bags while the plants are dormant.

  1. If you buy irises in a bag it is important to plant them out as soon as possible.

  2. Choose soil that has been enriched with rotted organic matter and has good water-holding capacity.

  3. Plant iris bulbs while they are dormant, and water in well.

  4. Do not be tempted to plant your iris deep, like a daffodil. Most iris’s rhizomes grow on or near the soil surface.

Of course, if you have purchased a variety of iris that likes water, follow the label to determine whether to plant in or beside the water.

Caring for your iris

Iris doesn’t generally require a lot of work once established. You might need to provide a stake for the flower stems of taller varieties if you are in a windy spot. Water regularly in drier weather to keep the soil damp, but not wet.

You can prune off spent flower stems. This stops the plant putting energy into setting seeds, and should redirect it into producing more flowers.

After a few years irises can become crowded, which reduces flowering and the quality of the flowers’ appearance. See “Iris propagation” for dealing with overcrowding.

Diseases and pests affecting iris

Sometimes aphids will attack young iris growth. These can be wiped away by hand or killed with a garden insecticide. It is important to control aphids, as they can bring diseases to your irises.

A few fungal and viral diseases will occasionally attack irises. They usually show up as brown spots on the foliage. Control with a garden fungicide. 

Iris propagation

Irises are propagated by division. If you have a large clump, dig it up in the cooler months, when it is not in active growth. You can use your hands to prise the clumps apart, but you may need secateurs to cut some of the rhizomes. Trim off dead or damaged roots and trim the foliage by about half before planting the separate portions as soon as possible.

If you like this then try

Clivia: evergreen bulb with showy orange flowers that tolerates even deep shade.

Daffodils: sunny yellow flowers are the hallmark of this favourite spring-flowering bulb.

Alstroemeria: long-lasting flowers for the garden or a vase. 

Start planting today

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