Bulb · Iridaceae
Bearded Iris
Iris germanica
Plant the rhizome shallow in full sun, leave it lean and dry, and the bearded iris returns every spring for years.
Full sun
Every 7–14 days
USDA 3–10
1–3 ft · 0.2–1 m
Overview
The bearded iris is one of the toughest flowers you can put in a garden. It grows from a fat surface rhizome rather than a buried bulb, and from that root it throws up sword-shaped leaves and tall stalks topped with ruffled blooms in late spring. The fuzzy strip on each lower petal is the beard that gives the plant its name.
Few perennials are this forgiving. Bearded iris shrugs off cold down to -40°F (-40°C) and heat past 100°F (38°C), handles drought once it has rooted in, and asks almost nothing in return. What it cannot stand is wet feet and being buried too deep, the two mistakes that rot the rhizome and stop the flowers.
Give it a sunny spot with soil that drains, set the rhizome shallow, and step back. Every few years you lift the clump and pull it apart, which keeps it blooming and hands you free plants to spread around or pass along.
Care
The short version: full sun and free-draining soil, the rhizome planted shallow with its back near the surface, watered sparingly once established, and fed lean. Divide the clump every few years to keep the blooms coming.
Light
Bearded iris wants full sun, ideally six or more hours a day, to bloom well. It will take a little afternoon shade, but too much shade trades flowers for floppy leaves.
Water
Once it has rooted in, this is a drought-tolerant plant that prefers things on the dry side. Let the top half of the soil dry out between waterings, roughly every 7 to 14 days, and skip overhead watering, which invites rhizome rot.
Soil
The one thing that matters most is drainage. A well-drained loam with some organic matter is ideal, sand is fine, and heavy clay needs sand or compost worked in. Keep the pH between 6.0 and 7.0.
Temperature
This is an exceptionally hardy perennial, comfortable from -40°F to 100°F (-40°C to 38°C), which covers USDA zones 3 through 10. Cold winters are no threat and most summers pose no problem.
Humidity
Ordinary outdoor humidity suits it, so there is no number to hit. Air movement counts far more than moisture in the air, since still, damp conditions around crowded clumps are what breed leaf spot.
Feeding
Feed lightly with a low-nitrogen fertilizer such as 5-10-10, once after bloom and again in early spring. Scatter it around the clump rather than on the rhizomes, because too much nitrogen feeds soft rot instead of flowers.
Pruning
Cut off the spent flower stalks after bloom so the plant doesn't waste energy setting seed. In late fall, trim the foliage back to 3 to 6 inches (8 to 15 cm) to clear out leaf spot and any borer eggs hiding in the leaves.
Repotting
Iris is not a houseplant, but the clumps do need lifting every 3 to 5 years in late summer once they crowd. Reduced flowering, packed clumps, and dead old centers that no longer bloom are the signs it's time to divide.
Size & spacing
Plants range from about 9 to 39 inches (23 to 100 cm) tall depending on the class. Set them 12 to 24 inches (30 to 61 cm) apart so air moves between the fans and leaf spot stays away.
When to plant
Bearded iris is planted as a rhizome in late summer to early fall, which gives the roots time to grab hold before winter. The reward arrives the following spring to early summer, when the stalks bloom around May, and a few cultivars send up a second flush later in the season.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Plant rhizomes in late summer to early fall
- Harvest: Spring to early summer (May), some cultivars rebloom
Hardiness
USDA hardiness zones: 3–10
Temperature: down to -40°C
Troubleshooting
Most iris trouble starts underground or at the base of the leaves, where you won't see it until something looks off. Catch the borer and the rot early and you can save the clump. Match what you find below, then act before it spreads through the rest.
Dying leaf tips with sawdust-like grains at the base
This is the iris borer, a caterpillar that hatches in spring, chews down the leaves, and tunnels into the rhizome below. Watch for the gritty frass near the leaf bases and crush the young larvae inside the foliage while they are still small. Once they reach the rhizome the damage is done, so dig out and destroy anything that has gone soft and tunneled.
Fix:
- Crush infected leaves early in the season
- Dig up and destroy affected rhizomes
Soft, foul-smelling rhizomes that collapse
A wet, mushy rhizome that reeks is bacterial soft rot, and it takes hold when plants sit in soggy ground, get buried too deep, or are smothered by mulch and rich feeding. There is no saving a rotted rhizome. Cut out and bin the affected plants, then fix the drainage and replant the firm pieces shallow, with their tops riding at or just above the soil.
Fix:
- Remove and destroy infected plants entirely
- Improve drainage and replant healthy rhizomes shallowly
Spotted leaves on a clump that is fading
Spots on the foliage point to fungal leaf spot, which spreads fast through a crowded clump where the air can't move. Strip off and destroy the marked leaves as you see them. If the planting has grown thick and tangled, lift and divide it so every fan gets light and a breeze.
Fix:
- Remove and destroy affected foliage
- Divide overcrowded clumps to improve air circulation
Toxicity
Bearded iris is not a plant to eat. The whole thing is mildly toxic and the rhizome is the worst of it, packed with irritant terpenoids that upset the stomach if swallowed and can leave skin red and itchy on contact. Keep the rhizomes away from pets and children, and pull on gloves before you dig or divide.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
A cat that nibbles the leaves or digs at a rhizome usually drools, throws up, and turns quiet and off its food for a while. The runs can follow. The rhizome is the part to keep well out of reach.
Dogs Mild
Dogs tend to chew the rhizome, the most irritating part of the plant, and the result is drooling, an upset stomach, and a dog that mopes around with no appetite. Loose stools are common too.
Horses Moderate
The same irritant compounds upset a horse's gut, bringing on drooling and diarrhea. Horses rarely seek iris out, but keep clumps away from paddock edges where a bored animal might browse them.
Rabbits Moderate
Iris is not rabbit food. The terpenoids that line the rhizome and leaves irritate a rabbit's digestive tract, so fence the plants off and never offer trimmings as a treat.
Livestock Moderate
Cattle, sheep, and goats can get a sore mouth and a churning stomach if they graze the foliage or turn up a rhizome. Most leave it alone unless pasture runs short.
Birds Caution
There is little to say one way or the other for birds, and the rhizome is an irritant, so treat iris as off-limits. Keep poultry and pet birds from pecking at the roots or foliage.
People Caution
No part of a bearded iris is meant for the table, and the rhizome is the most irritating piece if swallowed. Handling it can leave the skin red or itchy, so wear gloves when you dig or divide and keep children from chewing the leaves.
Wear gloves when handling rhizomes, as the sap can cause minor skin irritation or contact dermatitis.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Bearded iris is sorted into classes by height, from ankle-high dwarfs to stalks that reach past your knee. Picking the right class is mostly about how tall you want the flowers to stand.
Tall Bearded
The tallest and most widely grown class, standing 2.5 to 3 feet (71 to 97 cm) and carrying the big, ruffled flowers most people picture when they think of bearded iris.
Intermediate Bearded
A mid-height group at 16 to 27 inches (41 to 69 cm) that bridges the gap between the dwarfs and the tall types and often blooms a touch earlier.
Standard Dwarf Bearded
A compact class at 8 to 15 inches (20 to 38 cm) that suits the front of a border or a rock garden.
Miniature Dwarf Bearded
The smallest class, topping out around 8 inches (20 cm) and the first to flower each spring.
How to propagate
Bearded iris all but propagates itself, since a healthy clump outgrows its space and begs to be split. Division is the easy, reliable route, while seed is a slow path best left to breeders.
DivisionEasy
Mid to late summer, after flowering · Blooms typically resume the following season
Division is how almost everyone multiplies bearded iris, and the time to do it is mid to late summer once the flowers have faded. Lift the clump and break the rhizomes apart with your hands, keeping the young, firm pieces from the outside and throwing away the tired old centers that no longer bloom. Trim each fan of leaves down and replant shallow with the top exposed, and the divisions settle in to flower again the next season.
SeedModerate
Sow after seed ripens; named cultivars do not come true from seed · Several years to flowering
Growing from seed is really a breeder's game, since a named cultivar will not come true from its own seed. Sow the seed once it ripens and be patient, because a seedling can take several years to reach its first bloom. If you are not breeding, just cut off the spent flower stalks to stop the plant setting seed at all.
Myths
Bearded iris should be planted deep like a tulip or daffodil bulb.
Bearded iris grows from a rhizome, not a true bulb, and it wants to sit shallow with its back at or just below the surface. Bury it like a tulip and it rots and sulks instead of flowering. Plant it shallow and let the top catch the sun.