how to plant, grow & care for irises
complete growing guide
We plant lots of iris bulbs at Perch Hill to start off a long bulb flower succession. There are many different types, each with different care requirements (so do check the instructions for the one you buy), but here we focus on bulb irises and bearded irises.
First in the season are the winter-flowering bulb irises – Iris reticulata and Iris histrioides – which I love in pots on the doorstep to cheer me up and remind me spring is coming. Then there are the spring- and summer-flowering Dutch irises (Iris hollandica) and Siberian irises (Iris sibirica), which flower in May and June. And after that come the bearded irises (Iris germanica) and the Japanese water iris (Iris ensata), whose flowers can go on into July.
They are diverse in size and colour: there are tall varieties that are invaluable for providing drifts of colour in spring; there are deeply glamorous types in unusual coppery shades or in sugar-almond-pink; and there are delicate, miniature irises, which are so pretty in pots. And most irises have the added bonus of a delicate perfume.
They are cost-effective, too, because they are true perennials, so won’t need replanting. What’s not to love? Our carefully chosen selection of iris bulbs and rhizomes means you can have beautiful, rich, velvety iris flowers from February to July.
details
- Common name: Iris
- Latin name: Iris
- Type: Perennial Bulb / Rhizome
- Height: 15cm (6in) to 85cm (3ft)
- TLC rating: Easy
- Aspect: Full Sun to Part Shade
- Planting position: Borders, Containers
- Suitable for pots: Yes
- Good for pollinators: Yes
- Good for cut flowers: Yes
calendar
how to grow irises
where to grow irises
Soil type: Well-drained, fertile soil is best for irises. If the soil is unsuitable (such as heavy clay) growing in raised beds may be successful. For bulbs, you could also add grit to the planting hole, and for rhizomes mix grit into the soil you’re planting in.
Aspect & position: Full sun is ideal for most irises (bearded need full sun), though some will tolerate part shade (Iris reticulata and Iris histrioides are fine in part shade). For taller types, a sheltered position works well to minimise the impact of wind damage.
when to plant irises
The best time to plant bulb irises is in September and October, but they can be planted as late as November. Bearded iris rhizomes should be planted in August-October. Beardless pot-grown irises can be planted from spring to autumn.
how to plant irises
planting iris bulbs & rhizomes
If your soil is dry or poor, dig in well-rotted organic matter.
Bearded irises should be planted 30cm (1ft) apart and with the upper part of the rhizome partially exposed to get a late-summer baking. Avoid overcrowding of plants as this shades the rhizomes, meaning fewer flowers. Bare root rhizomes should be soaked briefly before planting.
Iris reticulata and Iris histrioides bulbs can be planted much more closely together at 10cm (4in) apart and 7cm (3in) deep.
You can add a mulch of organic matter each spring (but avoid contact with the exposed rhizomes as it could lead to rot). Remove dying foliage in the autumn.
growing irises in pots
The best irises to grow in pots are Iris reticulata and Iris histrioides.
You need a pot with good drainage filled with peat-free compost. Plant the bulbs at 7cm (3in) apart and 7cm (3in) deep.
Iris reticulata and Iris histrioides are lovely growing in shallow bulb trays topped with foraged moss – a pretty display for the doorstep.
Bulb lasagnes in a deep pot are another excellent way of using Iris reticulata: the iris bulbs make up the top layer, with two or three layers of tulips below.
You can easily lift and store the bulbs at the end of the season, planting them again the following autumn.
If you’d like a display indoors, bring pots inside and place on a sunny windowsill. Forced in this way, they will be in flower in February. Once in flower, it’s essential to keep them cool or they go over in 4 or 5 days. Kept cool, you should triple this flower life.
how to care for irises
watering
Irises don’t like to sit in waterlogged soil so ensure the soil or compost is free-draining and don’t overwater. Water in newly planted bulbs and rhizomes, and then leave them as they will be watered by the rain. Water during a prolonged dry period paying particular attention to pots and newly planted irises.
fertilising
You can add a layer of well-rotted manure or other mulch around the rhizomes and bulbs in early spring, but avoid contact with exposed rhizomes to minimise the risk of rot.
deadheading
Old flower stems can be cut after flowering – cut where the flower meets the foliage at the base. For bulbs, leave the foliage in place, and only remove it once it has fully died back to allow the leaves to photosynthesise and give the plant energy for the following year.
propagating and dividing
Bearded irises can be propagated by division. When clumps become congested, divide every three to five years. Do this six weeks after flowering as this will give the plants a chance to establish before winter.
Rhizomes grow outwards, so discard the centre of the plant to remove the oldest parts, and plant the outer rhizomes in improved ground.
lifting and storing
Bulbous irises are excellent for naturalising and can be left in borders or grass to clump up year after year.
If planting in pots, you can lift bulbs out and store them to plant the following autumn. Do this after the foliage has completely died back. Shake off the soil and leave them to dry before placing in a netted bag. Hang somewhere cool and dry, such as a shed or cellar.
seasonal checklist
spring
- Enjoy the first irises of the year.
summer
- Deadhead spent flower heads.
autumn
- Plant iris rhizomes and bulbs in pots, grass and borders.
winter
- Bring pots indoors to force for an early display.
pests, diseases & common issues
leaf spot
Brown spots and patches on the leaves that merge together is likely a sign of the fungal disease leaf spot. Remove and dispose of any affected leaves and clear away any dead debris below the plants.
rhizome or bulb rot
The fungal disease rhizome rot or bulb rot can affect irises. Before planting you may notice soft spots, slimy bits or a bad smell. If they are already planted, the leaves may yellow or lose their colour from the bottom up and the plant can flop and collapse.
If rhizomes are affected (bearded irises) it is possible to cut away the affected parts of the rhizome and replant in a different spot. But since irises are so cost-effective in the long run (returning year after year), you might decide it’s better to start again with healthy rhizomes. If it’s a bulb, then it should be lifted and disposed of.
why are my irises not flowering?
This could be a number of things. Perhaps overcrowding – bearded irises in particular do not like to be shaded by other plants. Shade in general may impact flowering. It could also be rhizome or bulb rot, or potentially the foliage was removed too early the previous year, weakening the bulb and affecting flowering this year.
do squirrels, deer or rabbits eat iris bulbs?
Squirrels will steal the bulbs. It’s unlikely deer or rabbits would eat the bulbs, but they may nibble on the foliage. Irises are toxic to rabbits.
why are my irises falling over?
Bearded irises can reach sizable heights and may fall over in the wind. Taller types should be planted in a sheltered position and you can even stake irises individually with a cane.
why are my irises drooping?
It could be rhizome rot. But also look out for underwatering during a drought, particularly for irises in pots. And for waterlogged soil or compost – irises will not enjoy soggy conditions.
why are my iris bulbs rotting?
Wet weather or damp and humid conditions can cause rot. When storing bulbs and rhizomes, ensure they are somewhere dark, dry and cool.
frequently asked questions
are irises poisonous to cats and dogs?
Yes, irises are toxic to pets.
are irises perennials?
Irises are perennial and will return year after year, making them excellent value for money.
do irises spread?
Yes, irises spread and can be lifted and divided every three to five years.
do irises need full sun? can irises grow in shade?
Bearded irises in particular needs full sun to flower and do not like to be shaded or crowded by other plants, but some Iris reticulata and Iris histrioides are happy in part shade.
can irises grow in pots?
Yes, it’s possible to grow irises in pots and Iris reticulata and Iris histrioides are perfect for this.
how do I tell if my iris bulbs and rhizomes are good?
Before planting, check for any soft spots, any slimy spots and also give it a sniff to check for a bad smell. If they are hard, dry and smell fine, then all is well.
should I soak iris bulbs before planting?
It’s not necessary to soak iris bulbs before planting, but bare root rhizomes should be soaked briefly before planting.
are iris bulbs edible?
Iris bulbs are toxic to humans and should not be eaten.
can I leave iris bulbs in the ground?
Yes, the bulbs can be left in the ground and will spread with each passing year.
are irises good for bees?
Some irises are more attractive to bees than others, but bees do pollinate irises.
how to cut & arrange irises
Irises are magical when the detail of their flower can be fully appreciated, which is what makes them such brilliant cut flowers. To enjoy them indoors, cut iris stems at their base and stand in deep water after cutting, leaving them somewhere cool for at least a few hours. Once arranged, remove any fading flowers and buds will continue to emerge.
Get more inspiration for displaying your flowers with our flower arranging videos:
