Saturday, 20 August 2016

the beauty of the Persian silk tree

My Albizia julibrissin f. rosea is flowering for the first time this year.  I am rather excited about this, since it is a very attractive thing, and I grew it from seed.  I don't know why, but seeing woody plants flower that you've raised yourself from seed has an additional frisson, over and above the pleasure to be had from herbaceous perennials, or annuals.  What started off as a parcel of seed packets dropping on to the doormat is on the way to being a tree.

Albizia julibrissin came originally from the near East, where it grows from Afghanistan to Korea, and has a distinctly exotic vibe.  It is a member of the pea family, and looks not unlike some kind of mimosa, except that it has pink flowers.  The leaves are large but airy and graceful, being divided into many sub-leaves which in turn are divided again into smaller leaflets.  The full botanical description as given in W J Bean puts it thus: Leaves doubly pinnate, with from six to twelve pairs of main divisions (pinnae), each of which consists of twenty to thirty pairs of leaflets, the entire leaf being 9 to 18 inches long, half as wide.  Each leaflet is 1/3 to 1/2 in. long, 1/8 in. wide, oblong, oblique due to the blade developing only on the side of the midrib towards the base of the pinna.  Who knew leaves could be so complicated?

They are a middling shade of greyish green, and have developed an attractive bronze sheen in the sun.  Garden centres offer named selections that have been picked out for their chocolate leaves, but I think the shading is prettier than all-over dark chocolate foliage would be.  The pink flowers consist mainly of tufts of long stamens, and have been gradually opening over the past week, with plenty more still to come.

The original species, Albizia julibrissin, is included in Bean but with the proviso that it is not hardy at Kew in the open, though he mentions that a form introduced from Korea in 1918 is quite hardy in the open at the Arnold Arboretum, and is of a smaller, more spreading habit than the common form.  I presume this is what has been dubbed A. julibrissin f. roseum, which has been awarded the RHS Award of Garden Merit.  AGMs are only dished out to plants judged in trials to be reliable in a range of garden conditions, and when I ordered my seed the comment in the catalogue (probably Chiltern) was that it was hardier than the plain form.

Certainly my plant wants to spread.  I first saw Albizia for sale at the plant centre, imported from an Italian nursery and a good ten feet tall with clean standard stems, and imagined my seedling would do that, but it is reluctant to make a main trunk.  I chose the likeliest one and tied it to a stake, then pruned the others last summer, but they have defiantly grown again and apart from the stake you couldn't honestly tell which is supposed to be the leader.  Last year when we visited the Hillier Arboretum I noticed a young Albizia in a bed near the house, a year or two ahead of mine and equally spreading.  Maybe that goes with the type, along with the increased hardiness and pinker flowers.  But, and here's a thought, it could be something to do with how the plants were raised.  The self sown Genista aetnensis now growing in the gravel are making much less branched and more tree like shrubs than their parent, which I grew from seed and planted out.  It was still quite small when I planted it, but started life in a pot, and through its life it insisted on making many more stems from low down than I wanted it to.  And I have read that Zelkova in the wild make tall trees when in cultivation they generally make multi-branched specimens like gigantic besom brooms, which is just what mine (also grown from seed and planted out while still small) is doing.

According to the RHS sapling Albizia should flower in three years, so mine has been a touch slow, unless last year's pruning inadvertently removed what would have been the flowering wood.  But it is to be flowering now on this year's growth, so I don't think that was the issue.  Architectural Plants offer some cultivation advice on their website, and explain that in the wild it experiences hotter summers and colder winters than we do here.  British summers may not be warm enough to ripen its wood, or to coax it into leaf before June, which can lead to problems with die back in the winter when the inadequately hardened growth is hit by frost.  My plant went into the ground in May 2011, and I haven't noticed it being desperately late into leaf, nor has it suffered from die back to date.  As I recall 2010-11 was the second of the recent hard winters, while 2011-12 was horribly wet, so it hasn't yet been tested in a really cold year.  Architectural Plants do reassuringly promise that I can prune it as much as I like in spring and summer.

I don't have a spare wall I could grow the Albizia against as Architectural Plants suggest, but our garden would probably count as very sunny, which is one of the situations in which they suggest it should be OK in the open.  The high light level was one of the factors cited by the lettuce farm in their decision to locate here.  And areas mulched with gravel get hotter than the equivalent space covered in an organic mulch or grass (I know I've read articles on that, but can't lay my hands on one to refer you to at this moment).  At any rate, after five years out in the garden the Albizia is coping nicely so far.  I have a second, since two germinated, and that lives in a pot in the conservatory, is a fraction of the size of the one planted out, and shows no signs of flowering. True, members of the pea family can be funny in pots.  An Acacia dealbata seedling given to me by a friend who germinated it from seed from her own tree (before the two successive hard winters killed it) never thrived, and eventually petered out and died, despite my very best efforts to care for it, and a Sutherlandia frutescens and several Lupinus 'Silver Fleece' raised from seed went the same way.  Yet again it has proved easier to keep something in the ground than in a pot.

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