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!


  1. This is a very good post. Love the pictures by the way.
    garden ornaments

    1. Hi there,

      Thanks! Glad you enjoyed reading it!