When to plant irises?
- Botanical name
- Iris germanica
- Family
- Iridaceae
Irises are planted from August to September. They flower from May to June.
Irises are perennial plants.
The iris grows from a rhizome that stays at the surface of the soil, with its top in view. In heavy clay a still larger part of the rhizome is left uncovered. Wet ground harms it, so no mulch goes over it, not even for winter.
A crowded iris clump is lifted and divided in late summer. The young rhizomes from the outer edge are used for replanting, and the old middle is thrown away, because it no longer flowers. A rhizome put in then roots before winter.
The rhizome is the most poisonous part of an iris and at the same time the part cut and handled during division. Its sap irritates the skin, so the work is done in gloves.
Irises through the year
- planting
- flowering
In short
Growing conditions
Are irises toxic to cats and dogs?
Yes. Toxic to people and animals, toxic parts: roots, seeds and sap.
Pests and diseases
Listed here is every problem for which the sources name this plant as a host. The problems are not listed in order of how common they are.
- Signs
- Colonies of small aphids sit on the shoot tips and the underside of the leaves. The leaf curls and puckers, and sticky honeydew is left on everything below. The viruses they carry are more dangerous than the feeding itself.
- Prevention
- Go easy on nitrogen, because soft sappy growth is what aphids are looking for. Encourage the predators (ladybirds, lacewings, parasitic wasps). Use a reflective mulch, which puts them off settling, and a strong jet of water to knock the colony off the tips.
- What to do
- Potassium soap works on contact and only while it is wet, so it has to reach the underside of the leaf. On drought-loving plants and in heat it can scorch, so apply it in the evening.
- Signs
- White blotches and streaks show over the leaves and flowers. In a heavy attack the petals turn brown and the buds do not open at all. On stored corms and bulbs there are rough grey brown patches.
- Prevention
- The thrips overwinters on stored corms and bulbs. It is most active from July to September. In a warm room it breeds all year, so keep the store cool.
- What to do
- Put up with light damage, see to a clean lifting and encourage the natural predators.
- Signs
- Brown to greyish spots with a darker edge appear over the leaves, spreading and running together in wet weather. The leaf dies from the tip down, while the rhizome stays sound.
- Prevention
- In autumn clear every leaf and all plant debris off the bed, because the fungi and the insects overwinter on that old foliage. Plant at an airy spacing and water at the base, not over the leaves.
- What to do
- Cut the affected leaves off as they appear and take them out of the garden, not onto the compost.
- Signs
- The rhizome softens into a mushy mass and smells foul. The fan of leaves yellows from the outside in and pulls away from the rhizome at a tug.
- Prevention
- The rhizome has to lie shallow, with its upper side at the surface and not covered by mulch, because buried and wet is what the rot needs. Remove yellow leaves as they appear, clear all foliage and debris in autumn, and keep fertiliser off the rhizome and low in nitrogen.
- What to do
- Cut the affected part of the rhizome back to healthy tissue and take it out of the garden. Clean the knife between cuts. For the home garden there is no product.
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Related plants
The plants below are in the same botanical family (Iridaceae).
Sources about the plant: ASPCA Toxic and Non-Toxic Plants, Clemson Cooperative Extension, GBIF Backbone Taxonomy, NC State Extension Plant Toolbox, Penn State Extension, University of Georgia Extension, University of Illinois Extension, Wikidata. Checked between 14 and 28 August 2026. The problem descriptions also draw on: Royal Horticultural Society, University of Wisconsin-Madison Division of Extension, Utah State University Extension.