The much-vaunted hot weather predicted to be associated with this season’s El Nino weather pattern has certainly arrived, and our gardens are showing the effects. Many plants are showing signs of water distress, and our lawn, which was still green a couple of weeks ago, has reverted to its usual summer brown.
It is at times like this that you appreciate a nice shade tree. You can pull out your favourite chair or lounger, fill up a container with liquid refreshment of your choice, grab the book you were given from Christmas and just chill out for an hour or two.
Last week, we took the head gardener’s 99-year-old aunt out for a drive around the back country roads behind Carterton, and to pick up some summer fruit – it was just a coincidence that the orchard shop also sells ice cream.
On the way home, she commented on the number of silk trees that were in flower, saying she thought they were beautiful trees.
It certainly is the right time for these trees to be flowering, as they make one of the best shade trees for summer. Botanically, they are called Albizia julibrissin, and almost all trees in New Zealand are the pink flowering variety called ‘Rosea’.
In the wild, this form grows mainly in northern China and Korea and is hardier than the usual type, which is generally found in warmer parts of Asia. A member of the mimosa family, it forms a lovely small deciduous tree with a generous spreading crown of branches covered with very fine leaves.
In common with other related plants, these leaves are photosensitive – they close up at night and during rainy periods. The effect is not quite as dramatic as in the Sensitive Plant, Mimosa pudica, whose leaves close and droop whenever they are touched, only to spring back to their original state minutes later, but it is still noticeable.
At this time of the year, the silk tree produces masses of lovely pink flowers, well described as “starbursts of pink silky threads”. They form upright cones of stamen, fully pink in some forms but neutrally toned with pink tips in other types. Either way, the flowers look not unlike those of pohutukawas, that have undergone a Barbie-like transformation.
One of the great advantages of this tree as a shade tree is the way it grows.
It forms a broad crown with many arching branches, making it easy to access, and the slender foliage casts a dappled shade, making it perfect to sit under, and possible to grow other plants underneath it if needed.
It is quick growing and is well adapted to coping with dry conditions. During its establishment, it may need a deep watering or two over the summer, but it will cope with most Wairarapa summers without any problem.
However, there is a slight concern about this plant. As a member of the wider legume family, it will sometimes set seeds carried in long, broad pods about 20 cm long. In some parts of New Zealand, especially northern areas and around Nelson, this plant has jumped the fence and naturalised out into the wild. Warmer temperatures could make this lovely tree become more of a threat.
Another member of the legume family makes a great summer shade alternative – the honey locust, Gleditsia triancanthos. This is another tree with delicate, fern-like foliage – although the leaves are larger than the silk tree’s, they will still provide a charmingly dappled shade.
The most common of these trees is probably the golden form, ‘Sunburst’, which was a great favourite in the 1980s. This form had bright golden leaves in summer, but they fade a little over the summer, ending up lime green. Like all its siblings, it copes well with dry conditions and does not worry about soil fertility at all. Its graceful, pendulous style of growth makes it perfect for a shade tree on a lawn.
This has a few flowers in spring – creamy coloured, they are quite scented and are followed by large seed pods.
There’s a little twist in the botanical name of this plant. The “triacanthos” part refers to the thorns that Gleditsias typically carry – they are fierce and well-avoided. Fortunately, this is a variety of the form called ‘inermis’ – literally “without a sting, referring to the fact that this variety is [thankfully] thornless.
There are a couple of other forms for the garden if golden-yellow is a bit too bright for you. ‘Ruby Lace’ is – well, I think you can work out what colour it is. The colour is deeper in the spring – over the summer, it changes to bronze.
‘Limelight’ is a toned-down version of ‘Sunburst’, bred in New Zealand, while ‘Emerald Cascade’ is bright green with a pendulous habit.