Rhizome
How to grow bearded irises
Iris germanica hybrids
Bearded irises need full sun and free-draining, neutral to alkaline soil, with the rhizome sitting on the surface where the sun can bake it. Plant or divide them from July to September, about six weeks after flowering, and they bloom in May and June. Most failures come from shade over the rhizome, planting too deep or rich feeding. Divide every three to four years to keep them flowering.
- Hardiness
- Fully hardy
- Position
- Full sun
- Soil
- Free-draining, neutral to alkaline
- Ideal pH
- 6.5 to 7.5
- Water
- Low
- Feeding
- Light feeder
Sowing and planting bearded irises
WhenPlant or divide Jul to Sep; flowers May to Jun
Starting off
Plant or divide Jul to Sep, 6 weeks after flowering, cutting young outer rhizome pieces 10 cm long with a fan of leaves, trimming the leaves to 15 cm and discarding the old centre; replant with the rhizome top in sun. Division every 3 to 4 years is the only practical method; seed takes 2 to 3 years and varies.
Spacing and planting
Plant 30 to 45 cm apart in groups of three with rhizomes pointing the same way; set the rhizome half-exposed on a ridge with roots spread down. Dwarf bearded types are fine in a 30 cm pot of gritty compost; tall types are not container plants.
Varieties worth growing
- 'Jane Phillips'
- Tall bearded, pale blue and scented. Old, vigorous and forgiving, which makes it the one to start with.
- 'Kent Pride'
- Tall bearded in chestnut brown with yellow and white markings; a reliable British-bred variety for a hot border.
- 'Sable'
- Deep violet-black tall bearded, strong against silver foliage and pale walls.
- 'Langport Wren'
- Intermediate bearded at about 60 cm in dark maroon. Flowers in May before the talls and stands up to wind without staking.
- 'Cherry Garden'
- Standard dwarf bearded, about 30 cm, plum purple in April and May. The size for a pot, a gravel bed or the front of a border.
Bearded irises month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing to do beyond firming back any rhizome lifted by frost.
- February
Pull away dead leaves and winter debris so the rhizomes are exposed to the light.
- March
First light feed, scattered around and not on the rhizomes. Hand weed; a hoe damages the surface roots.
- April
Dwarf bearded irises flower. Watch for slugs and snails in the fans.
- May
Intermediates, then tall bearded irises, come into flower. Snap off individual spent flowers.
- June
Cut each finished flower stem to the base. Second light feed.
- July
Start lifting and dividing congested clumps, six weeks after flowering.
- August
Main month to divide and to plant new rhizomes. Trim fans to 15 cm.
- September
Finish planting by the middle of the month. Water new plants in dry weather.
- October
Remove spotted and dying leaves.
- November
Clear all dead leaves from around the rhizomes. No mulch.
- December
Nothing to do.
Feeding bearded irises
A light feeder that wants phosphorus and potassium but very little nitrogen, which softens the rhizome and invites rot. Two small feeds a year at most, and none of it on top of the rhizome.
Low nitrogen, a little potassium, too much N causes soft rhizomes and rot. Let the rhizomes bake in the sun.
Feeding plan
Late winter before planting, only if a pH test reads below 6.5
Garden Lime (calcium carbonate)
About 0.5 kg/m², worked into the top 15 cm. Do not lime without a test; most garden soils do not need it.
March
100 g/m², the bottom of the label range, scattered on the soil between the rhizomes and watered in. A group of three plants covers roughly half a square metre, so 50 g.
June, straight after flowering
The same again, 100 g/m², to build next year's flower buds. Nothing after July.
March, dwarf types in pots
3 g per litre of compost on the surface, once: 36 g for a 30 cm pot holding about 12 litres. The label allows fortnightly feeding from first flowers, which is more than an iris wants.
After dividing, July to September
1 g per litre of water as a drench at replanting and again 2 to 3 weeks later to help new roots.
Signs to watch
Lush leaves and few flowers
Shaded rhizomes, buried too deep, or a nitrogen feed
Lift and replant exposed in sun; bone meal and sulphate of potash in Mar, never manure
Rhizome soft and smelly
Rot from wet
Cut back and dry
Pests, diseases and problems
A fan of leaves yellows and falls over; the rhizome at its base is soft, wet and foul-smelling
Bacterial soft rot, entering through slug or tool wounds and encouraged by wet soil, shade and nitrogen
Lift the clump in dry weather, cut back to firm, clean, white tissue with a knife wiped between cuts, and leave the cut faces to dry in the sun for a day before replanting in a fresh, better-drained spot. Bin the rotten pieces.
Oval brown spots with a yellow edge on the leaves, joining up after flowering until the leaves die back from the tip
Iris leaf spot, a fungus that thrives in wet summers and overwinters on old leaves
Cut off affected leaves below the spots and bin them, and clear every dead leaf in November. Plants in sun with space round them suffer least.
Leaves rasped into ragged strips, holes gnawed in the rhizome, petals shredded
Slugs and snails sheltering in the fans and old leaf bases
Pull off dead leaves so there is nowhere to hide, hand-pick at dusk and keep neighbouring plants from flopping over the rhizomes.
Small rusty-orange to dark brown raised pustules on the leaves in late summer
Iris rust
Remove and bin affected leaves and avoid nitrogen feeds, which produce soft growth. It rarely harms flowering.
Newly planted rhizomes rock loose or lift out of the soil over winter
Wind-rock and frost heave before the roots have anchored
Trim the leaves to a 15 cm fan at planting, plant by mid September so roots form in warm soil, and firm lifted rhizomes back with your hand after frost.
Pruning
Pruning and care
Cut flower stems to the base after flowering in Jun and trim leaves to 15 cm fans in Aug to reduce wind-rock. Divide every 3 to 4 years in Jul to Sep, replanting the youngest rhizomes. Never mulch over the rhizome and keep neighbours from shading it. No staking for most; fully hardy, no protection. Remove dead leaves in Nov.
Good to knowPlant rhizomes shallow, half-exposed to the sun; divide every 3 to 4 years after flowering.
Growing bearded irises in pots
Only the dwarf and smaller intermediate bearded irises suit pots; tall ones are top-heavy and outgrow a container in a season. Use a wide, shallow pot of about 30 cm with large drainage holes and a loam-based compost mixed with a third grit. Set one to three rhizomes on the surface with the tops exposed and the fans pointing outwards so the new growth heads for the middle. Stand the pot in the sunniest place you have, water when the top few centimetres are dry from March to July, and keep it out of saucers. Divide and repot every two years in August.
Bearded irises: common questions
Why are my bearded irises not flowering?
The usual cause is a rhizome that is shaded, buried or overcrowded. Bearded irises set their flower buds in summer when sun warms the top of the rhizome, so neighbouring plants flopping over them, a mulch, or planting too deep all stop flowering. Clumps older than four years flower only at the edges and need dividing. Newly divided plants often miss a year, and nitrogen-rich feeds give leaves instead of flowers.
Can I move bearded irises in spring?
You can, and the plant will survive, but you will probably lose that year's flowers. The best time is July to September, about six weeks after flowering, when the plant makes new roots quickly in warm soil. If a spring move cannot wait, lift a large clump with as much soil as possible and do not divide it until summer.
Can bearded irises grow in clay soil?
Yes, if you lift them out of the wet. Plant on a ridge or low mound 10 to 15 cm above the surrounding soil, with grit worked into the planting area, on a slope or raised bed if you have one. Clay that sits wet round the rhizome in winter leads to soft rot. On improved clay in full sun they flower very well, because the soil is fertile and usually close to neutral.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.