The Ultimate Iris Growing Guide
Irises are easy to grow, showy and elegant with an unmistakable spectrum of flowers.
Grow in pots or in borders where they compliment late tulips, daylilies, alliums and other spring-flowering plants.
Irises are true perennials, meaning they come back year after year reliably with little intervention by the gardener.
Key plant details:
- Choose from several varieties with Iris Reticulata the best choice for spring colour.
- Grow from bulbs, rhizomes/bare roots.
- Minimal water, feed and maintenance.
- Perfect for sunny spots and slight shade with good drainage.
Height: Up to 120cm (4′)
Spread: 30cm (1′)
Borders, beds and containers
Full sun or partial shade
US zone 5-9 and hardy in all parts of the UK. Irises are evergreen in mild climates but will shed their leaves during a UK winter
Water & Feed
Once established, only water during droughts. Apply manure, leafmould or similar once a year in spring
Tulips, late daffodils, daylilies, alliums and other late spring-flowering plants
Plant bulbs up to 15cm deep while rhizomes should be planted with the tip at ground level
Late spring into summer
The Best Irises For Spring
There are several irises that perform well in spring:
Iris reticulata – A popular choice for late winter and early spring colour. Each stem on this dwarf (15cm/6″) iris contains 6 deep purple flower petals, with one displaying a yellow and white ridge. Locate in pots, window boxes and rockeries.
Dutch irises – These grow from teardrop bulbs and rise 45cm to 60cm (18″-24″) tall, making them perfect for mid-border. Foliage may appear in winter with flowers on display in early to mid-spring.
Siberian irises – The tallest iris for spring and perfect for making a statement, expect growth of up to 1.2m (4′) and 5 violet-blue, veined petals per stem.
How to Grow Irises in the UK
How Do Irises Arrive?
Irises are sold as either bulbs or as rhizomes (root stalk) and are planted in autumn.
Where is the best location to plant irises?
Irises prefer full sun but some varieties such as the shorter Iris reticulata will cope with some shade.
Taller varieties should be grown in a sheltered location to protect them from the wind.
All irises prefer well-drained, fertile soil. If the soil is unsuitable, grit and organic matter can be added to improve drainage.
Iris reticulata and Iris histrioides are the most suitable varieties for pots.
Will irises survive the winter?
Irises are winter hardy in the UK and will survive the cold winter months.
Are irises evergreen?
In the UK, irises will lose their leaves and fully die back in the summer and autumn but in warmer climates or during mild winters, they may retain their leaves throughout the winter.
What soil conditions are best for irises?
Well-drained, fertile soil is best for irises.
When and how should irises be planted?
The ideal planting depth will depend on whether you’re planting a bulb or a rhizome.
Bulbs should be planted relatively deep, around 15cm (6″), while the rhizomes should be planted horizontally with the tip of the root just at ground level and not covered by soil.
Taller varieties should be given some space and planted around 30cm (1ft) apart.
Potted irises should be grown 10cm (4″) deep and about 7cm (3″) apart. They can also be layered with other bulbs (bulb lasagne).
The best time to plant most irises is in September and October, and in November at the latest.
Which pests and diseases affect irises?
Squirrels may dig up and steal the bulbs.
Leaf spot is a common disease and is spread by overhead watering.
Bulb and rhizome rot is a fungal disease that can lead to yellow leaves, discolouration, and collapse of the stems. The best treatment is to remove and dispose of affected plants as soon as the disease is discovered.
When do irises flower and how long for?
Irises will flower from early spring to mid-summer and each variety should put on a good show for a couple of weeks.
Are there any special water and fertiliser requirements?
Irises only need extra water during dry spells as they prefer slightly moist but never waterlogged soil.
They prefer nutrient-rich soil, so well-rotted manure or another type of mulch, applied in the spring, would be of benefit.
Are irises toxic or harmful to humans and pets?
All parts of the iris plant are poisonous top pets while the bulbs are poisonous to humans if consumed.
More information about the adverse effects of consuming irises can be found here.
How to Care For Irises After They’ve Finished Flowering
The flowerhead can be removed once the show is over by cutting it where it meets the foliage. The remainder of the plant should be left to die back naturally to continue to photosynthesize and send energy to the bulb or rhizome for next year’s growth.
If the irises have become congested, they can be lifted, divided, and replanted about two months after flowering; this should give them enough time to recover before winter.
Potted irises won’t last more than a year or two if left in place over winter, but they can be lifted after flowering, dried and stored in a garage or shed.
Iris Companion Plants
These six spring-flowering plants go well with irises:
A far more in-depth guide to iris companion planting can be found at the English Iris Company’s website.
Here are some solutions to common iris problems:
Irises Not Flowering
There are several reasons why irises may stop flowering:
- Overcrowding, often due to naturalisation and the irises spreading in the same spot for several years.
- Lack of sunlight is a common reason why irises may refuse to flower.
- The foliage was removed or tied in a knot the previous year – this stops photosynthesis and leads to a weak bulb.
- Bulb or rhizome rot.
- The rhizome should never be buried under the soil or foliage of other plants.
This is often because of:
- Squirrel theft.
- Bulb rot/disease.
Irises Flopping Over
Some irises may flop over and the stems may break:
- The bulb was planted too shallow.
- The location is too exposed to the wind.
- Taller types may need staking.
10 Quick Tips For Growing Irises
Daniel, our resident author, has ten quick tips for anyone wishing to grow irises for the first time:
- Get the bulbs or rhizomes planted in autumn but pay attention to the planting depth as rhizomes need to be planted shallow or they will rot.
- Not all irises are suitable for pots, go with Iris reticulata or Iris histrioides, both of which are easy to grow in containers.
- Potted irises should be grown in bulb fibre compost or similar.
- Don’t worry if the plants start growing early; it’s not uncommon for bulbs to put up shoots during mild winters. In fact, it’s becoming the norm.
- Taller types are prone to wind damage, so locate in a sheltered spot and consider need staking.
- There’s no need to overdo it with water and fertiliser. Instead, only water during dry spells and just apply organic mulch once a year in the spring.
- Don’t prune off the foliage until at least six weeks after flowering so it can send energy back to the bulb.
- Consider lifting and dividing irises if they become congested; you’ll get more blooms if they are given extra space.
- Pay close attention to the flowering time of the irises, so the blooms coincide with that of companion plants.
- Sunny spots are best, but some will perform well in the shade, too; just keep them away from full shade or soggy parts of the garden.
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More From Daniel Woodley:
This guide to growing irises in the UK was created by Daniel Woodley here at DIY Gardening and was last updated in January 2022.
Daniel is a keen amateur gardener who also manages a large residential landscape in addition to his own mid-size garden.
He also enjoys growing vegetables and fruits as well as his herbaceous border and container garden.
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