Water-loving iris adds splash
While all irises are beautiful flowers, there are some kinds that have a special affinity with water. The water irises have an attractive lushness of flowers and foliage, as might be expected of plants that have a plentiful supply of water. These species have long been cultivated in Japan, where some kinds are native. Their flowers are large and flattened in shape, unlike most irises, which have upright and drooping petals of a similar size. Their shape gives the impression they are floating when seen against a water surface.
The most spectacular kinds are not all that well known here and are only grown by enthusiasts. The Japanese water iris is Iris ensata, with flower stems to about 90cm, the flowers held above the foliage at the top of the flower stems. A related species, Iris laevigata, is also from Japan and both species are found in China, Korea and Siberia too. They have similar broad, flat flowers in shades of white, lilac, blue, violet and dark purple. A few selections have pinkish, or pale purple, shades.
The lighter-coloured kinds can be spectacular in the evening light, while the darker kinds are better by day when their dark shades add depth to their surroundings.
The most widely grown in gardens is the Siberian iris, which likes moist, humusy soil, though not wet or with free water. It has smaller flowers with narrower petals and is robust and easy to grow, spreading slowly to make a good clump. The flowers are carried in large numbers in a clump of flower stems over narrow, upright, grassy leaves. It is usually blue but there are lovely purple-shaded kinds, such as 'Sparkling Rose'. The flowers are produced in June, sometimes earlier.
The yellow flag iris is a native species with tall stems and bright yellow flowers. It is widely seen in the countryside growing in marshy areas and the low-lying parts of wet fields.
It can be a bit too big for garden use but it is very pretty if it can be accommodated in a wild garden or a semi-wild, wet corner. It flowers in early summer.
Any of these irises can be grown in moist soil with plenty of humus, but only Iris laevigata thrives in free water more than a few centimetres deep.
Even one clump of any of these irises is spectacular, especially the large-flowered kinds. They look even better when clumps are placed where they play off each other.
Water iris can also be grown in a large pot, with the drainage hole partly or fully blocked to maintain damp soil.
Caterpillars are eating my birch
Q I've a beautiful white birch tree that has recently become infested by miniature green caterpillars and they are chewing the leaf edges and arch upwards. Can you please advise how I can remove them before my poor tree ends up leafless?
G Smith, Dublin
A The caterpillars along the edge of the leaves are sawfly caterpillars. They feed for a couple of weeks, then pupate and turn into adults. Although the feeding can look quite dramatic, the damage to the tree is minimal and the tree will re-grow leaves. You are unlikely to see these caterpillars again.
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