Saturday, 24 August 2013

A Trip to Ness - Birch, Sorbus and Much, Much More!!

Earlier this week I made a trip to the north west, to Ness Botanic Gardens in Cheshire, holders of a Plant Heritage National Collection of Sorbus, a significant collection of birches (Betula), along with numerous other plants of botanical and horticultural significance.

A view across the rock garden at Ness
My particular area of focus on this visit was the aforementioned collections of Betula and Sorbus, and I had arranged to spend the duration of my visit in the company of Dr Hugh McAllister, who co-wrote the recently published Betula monograph (as mentioned previously), along with the Sorbus (rowans) monograph,published in 2005. The gardens botanist, Tim Baxter co-hosted my visit which happily coincided with that of Paul Bartlett, manager of Stone Lane Gardens, which I visited back in May. We had the further pleasure of being joined by the much travelled and esteemed plantsman Chris Sanders. All set for some serious plant study

Among those looked at early on were specimens of B. megrelica and B.medwediewii, two similar shrubby species from Georgia. The former is restricted to Mt. Migaria with little is known of it and Paul was particularly keen to study the Ness specimens in comparison with B. medwediewii, as those growing with him at Stone Lane Gardens are very similar, though growing side by side here the differences in leaf size, shape and texture along with shoot colour were quite apparent. Having studied B. medwedewii in the wild recently (his report is available here!), Paul is keen to return to Georgia shortly in search of B. megrelica.

Hugh and Tim discussing B. megrelica and B. medwediewii...

Paul collects foliage samples for comaprison with the plants at Stone Lane Gardens

Continuing through the garden we observed a fantastic specimen of Populus glauca. One of the large leaved or necklace poplars (section Leucoides), we admired both its foliage and form - a fantastic tree, growing very well!

Populus glauca at Ness. It's glaucous foliage is apparent, even in this photo! 

We then came across another birch I had observed (and been given a specimen of for Westonbirt!) at Stone Lane, B. ashburneri, though this was a larger example than any I had seen there. Not far from this was a seedling grown on from this species, which although of possible hybrid origin (with the closely related B. utilis) is regardless a fantastic tree with great horticultural potential.

A plant grown from a seedling of B. ashburneri, showing good promise

After a brief pit-stop, we began to focus slightly more on some of the pinnate leaved Sorbus, as well as numerous other woody subjects en route. Many of the Sorbus held fruit at various stages of ripening, with some looking simply stunning!

Fruit and foliage of Sorbus aff. vilmorinii

Sorbus sp. KR6918

The distinctive foliage of Sorbus helenae. There was barely any fruit left on this specimen,
with the birds particularly fond of it! 

Eventually moving out of the more formal areas of the garden into meadow, we studied further birch and Sorbus species, observing a particularly fine young specimen of S. aff. wilsoniana that Chris is particularly fond of. With it's glossy foliage and fruit held in large clusters, it really is a great tree with true horticultural value!

The fine young specimen of Sorbus aff. wilsoniana with fruits yet to mature

This part of the garden (down towards the Dee estuary) formed much of the area used by Hugh for the research for the Betula monograph and it is an immensely valuable site to study the different provenances of Betula species. It was great to see far more variation within different species than you often come across in cultivation, as well as being highly educational!

Bordering the site the diversity continued and whilst to the uninformed the boundary may appear to be comprised of more common species of birch and alder (Alnus), it is packed with rarities and recently introduced material! A truly fantastic resource!

No ordinary hedgeline!! 

Moving back towards the more formal areas of the gardens we passed by some old nursery beds, again replete with an array of arboricultural goodness! Passing along the top one of the beds, my eye was caught by a specimen of the Acacia relative Albizia julibrissin, which was an unexpected treat! Having seen this most recently at Cambridge University Botanic Gardens last month, my only experiences of seeing it had been in areas in the eastern United States, where it enjoys the hot summers (and a little too much in some areas further south, where it has become invasive). Neighbouring this tree was what appeared to be a specimen of Eucommia ulmoides. Not entirely sure at a distance of 30 or so feet, myself and Tim ventured through a near impenetrable body of bramble to seek confirmation. On reaching the tree and tearing the leaf in half for evidence of latex (a tell-tale i.d feature of the species), I was delighted to find that it was indeed EucommiaFantastic! Brushing past (or more accurately avoiding being torn by) an Aralia elata on the way out we made our way to a bench where Chris had taken a seat. Informing him that it was indeed E. ulmoides, as he had suggested, he remarked that we could have saved ourselves ten minutes there, but hey, you gotta do what you gotta do!!

Tim amid the trampled undergrowth, in front of the Aralia, Eucommia, Albizia et al

We then worked our way back up towards the nursery, where Chris gratefully received a fine selection of plants to take away with him. All in all, a fantastic day amongst the trees!

Aside from studying the plants growing in the collection, I had brought with me from Westonbirt a number of specimens (both birch and Sorbus!) for identification/verification and Hugh, Tim and I spent a few hours around a table in the library at Ness on Wednesday morning observing the finer characteristics of these, making more than a few re-identifications of specimens along the way! The pinnate-leaved Sorbus can be a particularly confusing group and like many collections Westonbirt has (or had!) it's fair share mis-identified plants, owing to a combination of factors, including having specimens of unknown and hybrid origin as well as cases of perpetuation of names mis-used in the trade, to add to the confusion!

Having dealt with the Sorbus specimens,
Hugh studies one of the trickier birch, as Tim refers to the book

Among the specimens for identification were those that had only been identified to genus level and among these there certainly some of particular interest. Along with wild sourced S. pseudovilmorinii were three that proved to be S. munda. Hugh informed me that this has been collected only once, and though we have no accession details of these particular plants, we now know we hold some of the original material! Such occurrences highlight the value of the verification work we are undertaking and helps increase the value of the collection whilst informing us as to our future management plans.(More on our Sorbus later!).

So having had a fantastic time out in the gardens (I have given only a mere snippet here!) and studying leaf and fruit samples, I now have myself quite some work to do in amending and updating the all-important database here at Westonbirt. And oh yes, keep a look out for a few label changes!!

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!

Friday, 14 June 2013

An East Coast Favourite at Westonbirt - The Tulip Tree

For some visitors to Westonbirt, the tulip tree (Liriodendron tulipifera) is among the first trees they come across, with a maturing specimen growing on the borders of the current main car park. Others may notice a young specimen growing close to where a large Norway maple (Acer platanoides) once stood near Waste Gate at the entrance to Silk Wood, whilst those who make it as far as Jackson Avenue in the Old Arboretum will see the examples that make up part of the unique species combination of this avenue (the others are lime Tilia x europaea and cedar Cedrus atlantica, flanked by beech Fagus sylvatica and yew Taxus baccata). Numerous specimens are dotted around the collection, including a number of recent plantings from wild sourced seed.  

Liriodendron tulipifera is a member of the primitive Magnoliaceae and has just one other member of the genus for company, L. chinense (from China, as the name suggests!). The latter is more of a rarity at Westonbirt, with rabbits (who seem to be particularly fond of species in the Magnoliaceae) playing no small part in the demise of our mature specimens in recent years. We currently have just one specimen, located not far from Loop Walk in the Old Arboretum, but rest assured, new plants are on the way!

Introduced at some point in the mid to late 17th century, there are a number of venerable specimens of L. tuipifera around the country, but none have quite achieved the stature of those in the surviving old growth forests in its native range on the east coast of the United States, which I was privileged to see back in 2010 (courtesy of the Friends Of Westonbirt Arboretum). There, they attain heights of 120 feet and equally impressive girth (see photo below!) and are every bit as impressive as they sound.

A monumental wild specimen of L. tulipifera

Both species of Liriodendron are notable for their unusual leaf shape, which are four lobed with a broadly notched apex, appearing almost to have been cut. The leaves of L. chinense are ‘narrower waisted’ than those of L. tulipifera, offering a useful characteristic when distinguishing between the two. Both are also known for their tulip-like flowers, hence the specific epithet tulipifera of the American species. Our L. tulipifera aren't in flower just yet this year, but should be soon, so time keep a close eye on them! 

Slightly dull in colour, the flowers of the two species differ in size, with those of L. chinense being smaller, whilst also lacking the orange pigmentation present in L. tulipifera (see photo below). Our sole L. chinense is still a bit on the young side to be flowering quite yet. As well as flower and leaf characteristics, the Chinese tree also tends to attain a smaller size than its American counterpart, at least in cultivation. 

L.tulipifera flower

There is also a hybrid of the two found in cultivation, of which we have a fine example on Broad Drive in Silk Wood. Planted in 2002, it is intermediate in leaf characteristics of both parents and though again yet to reach the age where we would expect to see flowers, it is certainly showing plenty of hybrid vigour, so we shall eagerly watch this space!!

Liriodendron tulipifera x chinense leaf

Tuesday, 4 June 2013

A Rare Birch for Westonbirt

Returning from my recent visit to Stone Lane Gardens I was accompanied by a specimen of a rather rare birch – Betula ashburneri. The plant was a gift from Paul Bartlett, the Garden Manager at Stone Lane, for the collection at Westonbirt.

As described in the new Betula monograph, the species was ‘discovered’ in 1997 when on an expedition in south east Tibet, morphological differences were observed between the B. utilis at lower altitudes and those growing around the tree-line, by plant hunters Hugh McAllister and Keith Rushforth. Whereas lower altitude B. utilis tend to be single stemmed trees, those observed higher up were multi-stemmed bushes. Along with this difference in form, these high altitude specimens had smaller leaves with fewer veins than B. utilis as well as small, erect fruiting catkins. Whilst these plants could have been just a peculiar form of B.utilis, subsequent chromosome counts established them as genetically distinct. Examples of B. ashburneri were also found in cultivation from an earlier collection of B. utilis, along with a possible hybrid of the two. The species is named after the late Kenneth Ashburner, creator of Stone Lane Gardens and co-author of the aforementioned (and excellent!) monograph.

A number of young examples of B. ashburneri growing  in a grazed area at Stone Lane,
complete with  alder catkins from a neighbouring tree, if you can spot them!

The specimen I acquired has been potted on since its arrival at the propagation unit here at Westonbirt and currently resides in an air-pot, as do virtually all other plants on our nursery. The somewhat knobbly design of these pots (see image below!), with air holes and a perforated base, discourages root spiralling and encourages fibrous growth as roots grow outwards, finding their way to these air holes, where they then dieback (or are ‘air-pruned’), stimulating further growth behind the tip. A mass of roots results, with no need for any ‘teasing out’ during  planting, whilst we also find our trees establish quicker. Can’t wait to see this one out in the collection!

B. ashburneri, in an air-pot on the nursery at Westonbirt


Tuesday, 28 May 2013

Something (sort of) New to Look Out For

Visitors to Westonbirt may not yet be familiar with Taiwania cryptomerioides growing with us – in recent years there was a specimen growing close to the Forestry Commission offices but this succumbed following a combination of cold winters and dry springs, having been planted in thin soil in this area.

Now two young examples have been added to the collection. One of these is from wild sourced seed collected in 1993 by the Taiwan Forest Research Institute, which found its way to us via our colleagues at Bedgebury, whilst the other was a gift from Trellisick Garden in Cornwall.

One of the new specimens in the collection

Taiwania cryptomerioides is a monotypic conifer in the Cupressaceae, having previously been included in the now defunct Taxodiaceae.  Whilst it bears some resemblance to a number of other genera in its family (its specific epithet denotes the likeness of the juvenile foliage to the mature foliage of Cryptomeria japonica), DNA studies have illustrated that it is closely related to none. Consequently it sits alone as sole member of the subfamily Taiwanioideae.

Juvenile foliage of T. cryptomerioides

The species is native to the mountains of central Taiwan, parts of China and neighbouring Myanmar and a recently discovered (and Critically Endangered) population in northern Vietnam. The Taiwanese trees have been thought of by some to be a distinct species (T. flousiana) but authorities state that close comparison of these trees with those of mainland China reveal no consistent differences in morphology. In its native range it attains heights of 60 metres and is aptly described by some as the ‘Asian redwood’. It has attained far more modest sizes in cultivation in Britain so far but is undoubtedly one to look out for!

Although having been introduced to Britain in 1920, the records show only one specimen having been planted at Westonbirt until the aforementioned deceased specimen in 1997. This first planting was in 1941 in the area now known as Savill Glade and although we have no date of it being removed, it definitely isn’t there now! What can be said about the recently lost specimen is that it attained a respectable size in the 15 years it was growing with us so we are hopeful that the new additions will make an impact (and last quite a bit longer than that!). They are located on moist soils in the Old Arboretum on Specimen Avenue – a ride dominated by conifers, so they should fit right in!