The Ultimate Iris Growing Guide

Written by Hannah Miller. Reviewed and Fact Checked by Elizabeth Smith. Published to Spring Plants. Updated: 18th February 2023.

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I’ve always found irises easy to grow, showy and elegant, with an unmistakable spectrum of flowers.

They are a versatile spring plant that I’ve grown in pots and in borders where they’ve complimented my late tulips, daylilies, alliums and other mid-to-late spring-flowering plants.

Irises are true perennials, meaning they come back year after year reliably, and I’ve never had any notable issues with them.

Key plant details:

  • Choose from several varieties – I’ve found the Iris reticulata the best choice for spring colour.
  • Grow from bulbs, rhizomes/bare roots.
  • I’ve never had issues with water, feed or maintenance, as they’re mostly carefree.
  • I’ve grown them in sunny spots and slight shade with good drainage.

Size

Height: Up to 120cm (4′)

Spread: 30cm (1′)

Location

Borders, beds and containers

Sunlight

Full sun or partial shade

Hardiness

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

Companions

Tulips, late daffodils, daylilies, alliums and other late spring-flowering plants

Planting

Plant bulbs up to 15cm deep while rhizomes should be planted with the tip at ground level

Flowering

Late spring into summer

Purple iris flowers in field
Lilac iris closeup

The Best Irises For Spring

I’ve experimented with different irises over the years and I feel these ones will perform well in the spring here in the UK:

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. I’ve grown these exclusively in pots and they’re proven reliable.

Dutch irises – These grow from teardrop bulbs and rise 45cm to 60cm (18″-24″) tall, making them perfect for mid-border. I’ve noticed that the foliage and stem 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, mine grew up to 1.2m (4′) and produced 5 violet-blue, veined petals per stem. In my garden, they bloomed late in spring, around mid May.

How to Grow Irises in the UK

How Do Irises Arrive?

Irises are sold as either bulbs or as rhizomes (root stalk) and I’ve only ever 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.

I’ve previously struggled with the taller varieties in my windyswept garden, so in the future I will only grow them in a sheltered location.

From experience, I know that all irises prefer well-drained, fertile soil. I’ve previously added some grit to improve drainage, but my soil here is very compact and heavy.

I’ve grown both Iris reticulata and Iris histrioides in pots without any issues.

Will irises survive the winter?

Irises are winter hardy in the UK, and I haven’t had any issues with losses over the winter period here in my Surrey garden.

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, I’ve noticed that they sometimes 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.

I’ve always planted the bulbs relatively deep, around 15cm (6″), while the rhizomes horizontally with the tip of the root just at ground level and not covered by too much soil, no more than a sprinkling.

I believe that the taller varieties should be given some space and planted around 30cm (1ft) apart.

In my pots, I bedded the bulbs around 10cm (4″) deep and about 7cm (3″) apart. I’ve also had good results layering them with other bulbs (bulb lasagne).

I’ve found that the best time to plant irises in the UK is in September and October, and in November at the latest.

Which pests and diseases affect irises?

I’ve had problems with squirrels digging up bulbs in my garden, and they seem to love the iris bulbs, even more so than the crocus bulbs. In my pots, I’ve resorted to using chicken wire or mesh a few inches deep to stop the squirrels, and it’s been very effective so far.

Leaf spot is a common disease and is spread by overhead watering, but I’ve never had any issues.

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 but again, I’ve had these issues.

When do irises flower and how long for?

In my garden, the irises flower from early spring to mid-summer and most put on a good show for a few weeks.

Are there any special water and fertiliser requirements?

I’ve found that irises only need extra water during dry spells as they prefer slightly moist but never waterlogged soil.

My irises have always responded well to nutrient-rich soil, and I usually add well-rotted manure and compost in early spring to give them a boost.

Are irises toxic or harmful to humans and pets?

All parts of the iris plant are poisonous to pets, while the bulbs are poisonous to humans if consumed.

My dog has never been attracted to the bulbs and has never dug them up, either.

More information about the adverse effects of consuming irises can be found here.

Iris Hardy Summer-Flowering Bulbs, Ideal for Garden Borders, Mixed Colours Easy to Grow, Flowers Twice Each Year, 5 x Bearded Iris Re-Blooming Collection Bulbs by Thompson & Morgan
Bearded Iris Collection Garden Plant Hardy Perennial Flowering Garden Plants Easy to Grow Your Own 6X Bare Root by Thompson and Morgan (6)
Iris Hardy Summer-Flowering Bulbs, Ideal for Garden Borders, Mixed Colours Easy to Grow, Flowers Twice Each Year, 5 x Bearded Iris Re-Blooming Collection Bulbs by Thompson & Morgan
Bearded Iris Collection Garden Plant Hardy Perennial Flowering Garden Plants Easy to Grow Your Own 6X Bare Root by Thompson and Morgan (6)
Iris Hardy Summer-Flowering Bulbs, Ideal for Garden Borders, Mixed Colours Easy to Grow, Flowers Twice Each Year, 5 x Bearded Iris Re-Blooming Collection Bulbs by Thompson & Morgan
Iris Hardy Summer-Flowering Bulbs, Ideal for Garden Borders, Mixed Colours Easy to Grow, Flowers Twice Each Year, 5 x Bearded Iris Re-Blooming Collection Bulbs by Thompson & Morgan
Bearded Iris Collection Garden Plant Hardy Perennial Flowering Garden Plants Easy to Grow Your Own 6X Bare Root by Thompson and Morgan (6)
Bearded Iris Collection Garden Plant Hardy Perennial Flowering Garden Plants Easy to Grow Your Own 6X Bare Root by Thompson and Morgan (6)

How to Care For Irises After They’ve Finished Flowering

When I grow bulb plants, I always leave the foliage in place after the flowers have faded so the nutrients can be sent into the bulb, strengthening it for the next year.

Irises are no different but I usually nip off the stem after flowering and leave the foliage to fade naturally.

Irises can become congested, and I’ve previously lifted them about 2 months after flowering, divided them and then replanted them. They’ve recovered well and most of them bounced back the following year.

During my testing and experimenting, I’ve found that my potted irises rarely last more than a year or two if left in the pot for too long, but I’ve had better luck by lifting, drying and storing the bulbs until the autumn.

Iris Companion Plants

I’ve found that irises are versatile enough to mix with many other spring plants, but you may want to try these:

Also Consider

I’ve found a far more in-depth guide to iris companion planting at the English Iris Company’s website.

Problem Solving:

I’ve found irises easy and low maintenance, but here some solutions to problems I’ve come across:

Irises Not Flowering

My irises have been very reliable in my Surrey garden, but here 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, I’ve seen this in boggy gardens before.
  • The rhizome should never be buried under the soil or foliage of other plants. I always leave it on the surface or press it in by no more than a few millimetres.

Missing Bulbs

This is often because of:

  • Squirrel theft – an issue I have here.
  • 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, but I’ve found that hard work, and I’m trying to cut down on the number of plants I grow that require staking.

10 Quick Tips For Growing Irises

Daniel Woodley, our co-owner, has been growing irises for over ten years and has ten quick tips for anyone wishing to grow them for the first time:

  1. 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.
  2. Not all irises are suitable for pots, go with Iris reticulata or Iris histrioides, both of which are easy to grow in containers.
  3. Potted irises should be grown in bulb fibre compost or similar, add drainage material if you can.
  4. 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.
  5. Taller types are prone to wind damage, so locate in a sheltered spot and consider staking.
  6. 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.
  7. Don’t prune off the foliage until at least six weeks after flowering so it can send energy back to the bulb.
  8. Consider lifting and dividing irises if they become congested; you’ll get more blooms if given extra space.
  9. Pay close attention to the flowering time of the irises, so the blooms coincide with that of companion plants.
  10. 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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This guide was reviewed and fact-checked by qualified horticulturist Elizabeth Smith.

Explore: Elizabeth's profile and qualifications.

Meet The Author: Hannah Miller

Hannah is a keen gardener who grows organic fruit and vegetables in her Surrey garden and is moving towards a more sustainable lifestyle. 

She is also the proud grower of a dahlia and herb garden.

Hannah worked for the NHS for 12 years but also has a level 3 qualification in horticulture and is currently studying for her level 4.

More About Hannah Miller

Hannah Miller

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This iris growing guide was published by DIY Gardening

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