Monday, 22 July 2013

A Twist of Lime

Looking down the Main Avenue past the fountain,
with Sequioadendron giganteum, dating from 1855, on either side

Last week, myself and our propagator here at Westonbirt, Penny Jones, had the pleasure of visiting Cambridge University Botanic Garden. The purpose of our visit was to acquire cuttings from some of the Tilia (lime) species growing at the garden to propagate here for the collection Westonbirt.

Whilst we are holders of a Plant Heritage National Collection of hardy Tilia species, we currently do not have representatives of all the species that could grow with us and we are always seeking to improve the range of plants that we are growing here. There is a particularly good representation of the genus at Cambridge, owing in no small part to a former Director at the garden and Tilia specialist, Donald Piggott. His monograph on the genus was recently published, with a number of trees growing in the garden being of rare, wild sourced material, utilised in his study of lime trees.

This propagation work is also of benefit to Cambridge University Botanic Garden as from a conservation perspective it is important for these lesser grown plants to be distributed as widely as possible, while acting as an insurance policy against the loss of genetic material of their plants. We are grateful to those at Cambridge for affording us the opportunity to do this and, as always, it is great to engage with other collections for the benefit of all involved!

We arrived at the garden on Wednesday evening having visited a selection of supermarkets in the city on a quest for ice blocks for the cool bag - extras were required for safe packaging and transportation of the cuttings back to Westonbirt! Having met Tim Upson, the garden's curator, we wandered through the garden to visit some of the trees from which we were to take material from. Our visit coincided with one of the garden's summer concerts - talking trees with a jazz accompaniment on a warm July evening was a most agreeable experience!

Jazz at Cambridge University Botanic Garden
- one of the Sounds Green picnic proms

The first of the limes we were interested in was Tilia endochrysea, a species native to south-eastern China and considered a  primitive member of the genus. Discovered in 1918 but apparently absent from cultivation in western Europe and the USA until Donald and Sheila Piggott introduced it in 1993, the plant we were to obtain material from was derived from scion wood collected on that occasion. Growing well in a sheltered area of the garden, we were informed that it exhibits attractive reddish foliage in spring, a characteristic of this and other lime species (e.g T. henryana, growing with us currently), which will be a most welcome sight with us (we hope!) in due course!

Foliage of Tilia endochrysea

The next species we were keen to obtain material from was Tilia nobilis, another Chinese species, which was introduced from Emei Shan, Sichuan, by Roy Lancaster and Keith Rushforth, who collected scion material in 1980. The tree we were to take material from was derived from this introduction and conveniently for us, grows just next door to the specimen of T. endochrysea! A large leaved species, also with large inflorescence bracts, it would certainly make a welcome addition to the collection at Westonbirt!

Another specimen we were interested in was an example of T. platyphyllos. Native to much of Europe, including Britain, and while we grow a number of examples of this species, the particular  tree we were to take material from was used as the type specimen by Donald Piggott in his monograph on the genus and those at Cambridge are particularly keen to see this one grown more widely. We are grateful to have the chance to do so!

Returning to the garden the following morning, we visited a number of other limes which both parties would like to see propagated. Given the less vigorous growth on a number of these, Penny suggested it would be better to take material for grafting later in the year, as opposed to the cuttings taken of the aforementioned species.

Having a slightly hotter and drier climate than us, a number of tree species are more suited to growing in the conditions they are afforded at Cambridge, whilst some of the limes are less so, requiring damper conditions, as found with us here at Westonbirt! This is also a driver behind the Botanic Garden's desire to see these trees more widely distributed.

Beneath the crown of the champion Juglans major (labelled J. elaeopyron).
A tree appreciative of the Cambridge climate

Following a brief walk of other parts of  the garden, pausing to admire a number of the specimen trees (!), we then met up with Ian Barker, an Arborist at the garden, who was to assist in obtaining material from the trees in question. Using a pole pruner  in order to reach vigorous material up in the outer crown,  the required material was sensitively removed, then carefully packaged in the now adequately chilled cool bag, replete with newly purchased ice blocks!

Ian retrieving material from Tilia nobilis, as Penny packs it up

Having successfully obtained cuttings from each tree, we made our way back to Westonbirt, making full use of the air conditioning in the car (!), and once returned, tucked the cuttings away in the fridge overnight.

So on Friday, Penny and her volunteer assistant Chris, prepared the cuttings further, selecting the most suitable material and dipping them in rooting hormone, before getting them into pots. They were then transferred to space below the misting system, where they will stay for around 6-8 weeks, by which time they should have taken root, we hope! At this point, they will then be potted up and moved elsewhere on the nursery to continue their development.

Back at Westonbirt, Penny pops the cuttings,
dipped in rooting hormone, into pots

Then for the misting system!

It is hoped that in around two years, plants will be ready for planting in the ground, although success rates using these methods can be low so some losses are to be expected at an early stage. However, all being well (!), we should be able to increase the diversity of the collection here and of course, we intend to return some of the plants grown to Cambridge and in doing so, strengthen the collections held at both sites.

I shall endeavour to provide updates on the progress of these plants.... Watch this space!!

Bees enjoying the limes in the garden as much as we were!

Saturday, 20 July 2013

In Flower Now!! - But you might need binoculars!!

Visiting Cambridge University Botanic Garden earlier this week (more on this soon!), I made sure I passed by their specimen of Carrierea calycina, the Chinese goat horn tree, to check for flowers. I had been keeping an eye on our two specimens and was interested to see how this one was getting on, having first observed the plant growing on the lawn close to the glasshouses some time ago. On inspection, there were some flowers visible but most had gone over although I was assured that it had flowered well.

The Carrierea calycina at Cambridge University Botanic Garden earlier this week

So on my return to Westonbirt I paid a visit to our specimens, (seemingly) a male and a female, and although there was no evidence of any flowers on the male, to my satisfaction, I spotted a little more than half a dozen opening on the female along Morley Ride. However, they are all right at the top of the tree, which stands at around 20 feet tall! I understand that the flowers have a favourable scent, though there seems to be no chance of confirming this with our trees this year!!

The flowers opening at the top of our tree on Morley Ride yesterday

While I say that we have a male and a female, and having observed the flowers of both at close quarters, I am reliably informed that individual trees may possess both male and female flowers or possibly even hemaphrodites, as fruit has been produced on trees where all male flowers have been seen. I shall certainly be keeping a close eye on ours for any such occurrences!!

A female flower on our tree on Morley Ride in 2011

A male flower on our tree close to Savill Glade in 2011

Both our trees were planted in 1997 and flowered with us for the first time in 2011. Having heard, seen and read of more floriferous displays from other specimens in cultivation I am hopeful that we may see more on our trees in the future. But while it may not the most eye-catching of displays, and you might need binoculars to see the flowers, the tree is, of course, still worth seeking out!

Our tree on Morley Ride

Tuesday, 2 July 2013

A New Approach To An Old Favourite

One of my favourite specimens here at Westonbirt is this fantastic oriental plane, Platanus orientalis, photographed below.

It is found alongside Main Drive in the Old Arboretum and following the installation of a new path, linking this ride and Mitchell Drive, it can now be appreciated from a new angle (if you've stuck to the paths in the past, that is!). Growing on the corner of what is now a crossroads, the older routes passing the tree can bring you almost underneath it before you realise quite how magnificent a specimen it is, whereas the new path offers an unimpeded view as you approach, affording a golden opportunity to appreciate the sheer awesomeness of this tree. 

Taken in the sunshine yesterday, the photo does not do the tree justice at all.
You shall have to visit it yourselves!

Native to south eastern Europe, the species has been cultivated here since the 16th century and there are many venerable specimens both in this country and across Europe, with trees being aged at over 1000 years old. Locally, there is one of incredible stature south of Westonbirt at Corsham Court, near Chippenham, which is reputedly the tree with the largest spread in the U.K, averaging around 200 feet. Having been planted in 1757, this tree is a mere youngster and as is characteristic of many specimens, it has layered, rooting down and forming new stems, which have grown up and out, broadening the overall spread considerably (unfortunately I have no photos of this one - I shall have to pay another visit! For interest, there is also a sizeable black walnut, Juglans nigra, just to one side, and is being somewhat consumed by the plane!). Another at Westonbirt has layered similarly, and given the chance (and time!) would no doubt compete for overall spread size!

The specimen photographed above also has the unusual feature of  a 'natural brace' (see photo below). Long ago a branch appears to have grown from one of the major limbs towards another and then fused. It continues to put on secondary growth and provides additional structural support! Unusual but not unheard of, other species seem to have more of a tendency to fuse in the crown, for example the Persian ironwood, Parrotia persica, as can be seen just the other side of the path from this tree!

The 'natural brace', where branches have fused.

One of a few large oriental planes growing with us here, and while this species is the most seen of the Planes at Westonbirt, many people are more familiar with it's hybrid offspring, the London plane, Platanus x hispanica. Adorning many city streets and squares, it's attributes as a tree for the urban environment have long been recognised. Pollution tolerant, its young shoots and leaves are clad with hairs which trap particulates and once mature, these are then washed away by rain, taking any particulates with them. The tree also regularly sheds its bark and in doing so, lenticels that have been blocked by pollution are also shed, exposing fresh ones beneath, allowing continued gas exchange essential to the tree. This flaking bark is another feature and draws particular attention to the form and branching structure of the trees during the winter months. The tree is further suited to urban environments due to its tolerance of poor and compacted soils, and also of severe pruning (an unfortunate yet common occurrence on urban trees).

The form and bark can be strikingly attractive in winter.

However, the tree may not be to everyones taste, as the pollen can cause hay fever (I have seen the air thick with it on days in May in London parks!). Also, the fine hairs of its fruit can cause irritation to the eyes and skin as they disintegrate. Arborists tend not to work on specimens without a dust mask!

The other parent of the hybrid is the western plane or buttonwood, Platanus occidentalis. It is native to Eastern North America, where it is also known as sycamore, which has the potential to cause confusion!!  It doesn't tend to grow well here, with good specimens scarcely seen. There are a further handful of plane species, along with a number of selections of those mentioned above, and all things Platanus can be discovered on this particularly comprehensive website

The view looking back down the new path, towards Mitchell Drive.
Notice the Aesculus indica in flower on the left!