Perhaps we should rename November and call it Iris Month – at least in Central Otago. This is the month when bearded irises reach their full glory and various irises of a more slender build are in show-off mood. We’ve had more rain than usual this spring and irises have loved it – as have the weeds!
Last weekend I went on a tour of gardens in Alexandra and drooled over the huge clumps of beautiful blue, gold, and purple tall-beardeds planted against a backdrop of the wonderful schist rocks that are so characteristic of the town and its surroundings. We lived there once, and I wanted to move back again, immediately – with the right kind of garden naturally. Tall bearded, often mistakenly called flag irises are probably the most widely grown and easily recognised of all irises with their frequently brilliant colour combinations and their distinctive form, consisting of three upright standards, three falls, (the drooping petals or sepals) and three style arms which usually sit upright within the heart of the flower. Their name comes from the furry ‘caterpillar’ sitting on the haft of the falls and while the flowers of modern Siberian irises or Louisianas may look similar, a bright flash of colour known as a signal takes the place of the beard.
If you’re looking for stately flowers and emphatic foliage then bearded irises have both. If you want gorgeous hues and wild colour combinations, if you can’t stand fluffy, cottage-style planting, if you’re seeking a sleek tailored appearance in your garden, then go for bearded irises.
Essentials for bearded irises
- Rhizomes must be planted in full sun for at least half a day with the top of the rhizome, level with the top of the soil
- They need free-draining, humus-rich soil
- They don’t like clay or soil that is too acidic
- Ideal climate is a warm dry summer, followed by autumn rains, a cool winter and plenty of moisture in early spring
- They are heavy feeders. A mixture of 3 parts super phosphate to 1 part potash in spring and again after flowering works well though I find sheep pellets are a good all-round fertiliser.
- Rhizomes need to be divided every 3-4 years. Discard withered, non-productive rhizomes at the centre of the clump and replant the plump young rhizomes with a heaping of new soil. This is best done about one month after flowering to give the rhizomes a chance to develop good roots before winter.
Siberian irises are probably my favourites, though when it comes to irises, it’s bit like saying you have a favourite child. Graceful, elegant plants, they have flowers that rise above the foliage like delicate butterflies on long stems. Some of the newer hybrids have luxuriously wide, flatter flowers that are sometimes hard to distinguish from Japanese irises.
Unlike their rather stiff, bearded cousins, they grow in graceful clumps with fine fountains of slender leaves that are a stylish addition to a perennial garden right through summer and into late autumn when they turn brown and need to be removed. Their rhizomes, which store food for the plant and support the roots, are also much slimmer than the fat chunky structures that bearded varieties grow from.
Siberian iris species in their native habitat naturalise in damp meadows and reed swamps so, as you would expect, Siberians like rich, moist soil though reasonably good drainage is necessary. Well-established clumps will put up with periods of drought in late summer or autumn.
Siberians also like full sun. I have one in my garden which is a miracle of blue at present though it sulked in a shady corner for several years.
Early autumn is the traditional time to plant, especially where you can expect winter rain, but in reality Siberian irises can be planted, or divided and re-planted at any time. It’s often more satisfying to buy a plant in flower and if this is you, remember to water your new acquisition frequently once it is in the ground. Make sure the roots are never allowed to dry out until the plant is well established.
Dividing established clumps is not difficult so long as you have a sharp spade. Once the clump is dug out, split it and get rid of the spent rhizomes, old roots and the central part of the clump. Enrich the planting hole with composted manure mixed into the soil. Sit the new plant or division on a mound, spread out the roots and fill the hole, making sure the crown is 2-4 cm below the surface of the soil once the planting is completed. Another feed after flowering will make the plant feel cherished.
Mulching in summer, an absolute no-no for bearded irises, helps to retain moisture.
In the garden
Siberians are an asset in small gardens, because each plant forms a substantial enough clump to make a statement on its own and there is no need to plant them in groups. They come in a range of heights and because of their tall slender flower stems and clumping foliage, they add definition among fuzzier plants such as aquilegias or lavender.
Because they start blooming at the beginning of summer, they fit into the same season as roses and given that they like moisture they are also a good plant to situate near water. Rodgersias, hostas, filipendula and gunnera all like similar conditions and provide a contrast planted alongside narrow-leafed irises.
I hate to say it to Aucklanders but bearded irises are not the easiest plants to cultivate in the north but if you can provide the conditions they like you will succeed. For gardeners in the south, there is no more spectacular event in the garden in November than the flowers of the rainbow goddess.