The Plantsman’s Nursery

Bearded Iris Care Notes

August 29th, 2023

 Bearded Iris Care

Bearded Irises dislike being crowded in with other plants. They need an open position where they can feel the breeze. Poor air circulation, like sticky soil, leads to bacterial problems. To flower well, Bearded Irises need full sun for at least six hours a day. Gertrude Jekyll liked to grow Bearded Iris in rectangular beds set in stone paving. Plenty of air and sun, and easy to keep weeded. Plant irises in large masses, and experience the ultimate in nasal ecstasy.

Bearded Irises are easy plants in well-drained soil. They dislike sticky clay soils, which greatly increase the likelihood of bacterial problems. They prefer the soil to be alkaline or neutral. Acid soil should be limed. If the soil is heavy and needs breaking up, dig in quantities of spent mushroom compost or garden compost. If drainage is very poor, raised beds may be worth consideration. Iris beds need careful preparation to ensure you have a weed free start. Perennial weeds such as creeping thistle, nettle or ground elder are extremely difficult to weed from between established Iris rhizomes. Irises do not like excessive nitrogen; never incorporate animal manure into a new bed. Make sure any preparation work is completed a month before planting, so the soil can settle.

Irises should be planted between July and October as all their new root development is done in late autumn and early winter. Never transplant Bearded Irises in spring. Bearded Irises do vary in height and when planting an Iris border, try to grade the plants. In an island bed the taller plants should go in the middle, for a bed against a wall at the back. Bearded Irises, like many plants, look best planted in threes. If you plant just one rhizome of each variety the effect will be spotty. Planting distances is, as usual, according to impatience. But remember Iris rhizomes increase rapidly and close planting will necessitate frequent division. I plant Tall Bearded Irises 60cm. apart, Intermediate Bearded Iris 40cm. apart, and Dwarf Bearded Iris 30cm. apart. In the planting hole with each rhizome incorporate a tablespoon of slow release fertilizer. Never use an instant high nitrogen fertilizer. Bearded Irises hate a nitrogen rush, which leads to sappy growth and bacterial problems. Plant the irises with the top of the rhizome showing. Burying the rhizome can cause bacterial problems and may result in the Iris not flowering, as the rhizome will get insufficiently baked. Don’t worry if the Iris rhizomes seem rather insecure after planting. Within a month they will be strongly rooted. Water the Iris bed thoroughly after planting and water thereafter weekly until the end of October

During the winter, the irises’ leaves will die back. Dead leaves should be removed
Continue to remove any old foliage and weed carefully. When the Iris leaves are about 15cm. tall, sprinkle the Iris bed with a natural phosphate feed. As Irises approach flowering time, the mature fans, which will produce flowering stems, become swollen. Flowering for the dwarf varieties begins in mid-April, closely followed by the Intermediates. The Tall Bearded flower in late May and early June. During flowering time, spent flowers should be removed daily. Irises, once they have paraded their perfections, embrace putrefaction with shameful haste.
After flowering, break off all the old flowering stems. Do not cut back the leaves in summer, as these are essential for the development of the new rhizomes. On month after flowering feed with a natural feed high is phosphate not nitrogen. This will encourage the formation of new rhizomes.

Irises often need watering in dry periods in spring before blooming or after division and replanting. During hot dry summers, occasional watering may be necessary to ensure the new rhizomes continue to develop.

Bearded Irises also need to be lifted and broken up at least once every three years. If they are left longer the rhizomes tend to become congested and shade each other. Rhizomes should be lifted and replanted in late summer as new roots are made during the autumn rains. When lifting Bearded Irises, you can break off and discard old rhizomes, which have flowered, unless these are firm and will help anchor the plant when replanting. These will not flower again and they are worthless. Only trim leaves if you are replanting to reduced ‘wind rock’ and reduced transpiration this is not required if you are not moving the plant. Irises need their leaves to photosynthesise and produce food for next year’s flowering. Only remove brown leaves as they die back in the autumn/winter

Bearded Irises are troubled by few pests. Rabbits and caterpillars shun them. Slugs show only a mild interest. The biggest problem is bacterial infection. In our experience sprays and the like are not necessary. Good preventative hygiene is sufficient. A few basic rules. 1. When replanting irises, always replant into fresh soil. This will mean, if you wish to reuse an old bed, digging it out to a depth of 30cm. and refurnishing it with fresh soil. 2. Always plant Bearded Irises in an airy spot; good air circulation is essential. 3. Always plant Bearded Irises in well-drained soil. 4. Never plant Bearded Irises deep. 5. Always remove dead iris leaves. 6. Dig up and divide Bearded Irises before they become congested. 7. Do not water Bearded Iris with overhead sprinklers. 8. Never feed Bearded Iris with high nitrogen fertilizers. If you follow these rules, any losses suffered will marginal and the application of chemicals will be needless.

By Gillian Morris

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