Work experience at Wespelaar Arboretum and Herkenrode Gardens Monday 6th April – Sunday 19th April

The PGG meetings and garden visits often combine business with pleasure. It was during the study tour in Belgium last October 2014 that my idea of a work experience at Wespelaar Arboretum and the linked gardens at Herkenrode was first conceived. As an Italian gardener currently living and working in the UK, I am always keen to link myself with the European horticultural industry and people, potentially paving the way for a comeback one day. In addition to that, the Belgian gardens and arboreta struck me with their individual and well-defined character, of which Wespelaar and Herkenrode have truly reached its peak. Therefore, I expressed my interest in joining their team and, after a few e-mails were sent and some details arranged, in early April I was back on Belgian soil for a fortnights work experience. Spring is a good time for being at Wespelaar and Herkenrode, principally because of the Rhododendron and Magnolia collections. During my time there most of the white, pink and purple magnolias were in flower, with the first yellows just starting to bud out. Every morning, walking towards the gardeners’ messroom for the first gathering, I used to cross the open spaces of the Magnolia Meadow, where Magnolia species and hybrids have been cleverly interplanted with evergreen conifers. In the morning haze the view of the large and abundant flowers was magical; only the fragrance was missing, but a second opportunity was always given on my way back at the end of the working day, when the afternoon heat inflamed the blossoms.

The Artois Pond provides one of the most important focal points in the Arboretum

Concrete raised beds outside the nursery; The church of Wespelaar in the backdrop

In the Magnolia Meadow, important species have been grouped by sections and planted close together with their hybrids

(on the right, Head Gardener Philippe Crock taking close-up photos) The dappled shade of the woodlands nearby was the realm of the rhododendrons, the largest collection at Wespelaar. Plants are set out according to the different sections and subsections, so permitting comparison of closely related taxa. The natural conditions have been manipulated here in order to accommodate as many hardy rhododendrons as possible, so withstanding the local tricky climate which features harsh winters and early spring frosts. In the Verlat Wood for instance, the dense canopy of mature Corsican pines not only creates ideal dappled shade, but also provides protection, with average temperatures generally five degrees warmer in winter and cooler in summer. In addition to that, the needles of the conifers have over time built up a thick top layer of light acid soil. No surprise that many other beautiful ericaceous woodlanders such as Stachyurus, Corylopsis, Pieris and Enkianthus have found a home here! The Verlat Wood was one of my favourite areas within the Arboretum. Regardless of its relatively recent establishment, I found this a fantastic example of landscape design, where consistent ornamental as well as botanical qualities have been successfully achieved. The arboretum and gardens are joint run by a team of five gardeners, plus seasonal students. They share all the necessary tasks and duties on site, being responsible of both soft- and hard-landscaping. All the major tree work is contracted to a trusted external tree surgeon. I had the opportunity to work with all the members of staff and undertook a variety of different tasks both in the public and private areas. My time there was so diverse and intense that to describe everything in few pages would simply be unrealistic; the aim of this article lies instead in switching on the reader’s interest, perhaps encouraging a trip to Belgium! On my first day, Head Gardener Christophe Crock asked me to plant some hardy trees in the Arboretum: what a fantastic job to start with! This made me aware of some behind-the-scenes secrets of Wespelaar, such as the use of bamboo canes as guards against roe deer or the playing cards system for quickly marking the nursery plants. The following days allowed me to underpin my understanding on the Wespelaar approach, thanks to some inventory and labeling walk-arounds, where the state of the collections is recorded and updated. A major undertaking was the transplanting of an adult specimen of Acer griseum x maximowiczianum. This hybrid is a real beauty, combining the volcanic autumn coloration of maximowiczianum with the attractive, flaky bark of griseum; however, my abiding memory is of three gardeners (writer included) crouched on the back of the tractor, striving to balance the weight of the tree on the front loader!

Transplanting the hybrid paperbark maple to its new location The day after, I helped in the drainage work in the gardens at Herkenrode. The combined effect of the low ground level and clay soil leads to waterlogged patches difficult to work with. One of the winter jobs is the enlargement of the drainage system, consisting in underground perforated pipes which permit the water to flow away. On that occasion I joined Stan, a Polish gardener, who doesn’t speak a word of English, and, my French being equally non-existent, we managed to communicate (and finally get the job done) just by using our hands. What an universal language horticulture can be!

Drainage work in progress On the second week, the priority moved to the preparation work for the study day on lepidote rhododendrons, organised by Arboretum Wespelaar and the Belgian Dendrology Society which took place on Sunday 19th, my last day in Belgium. I helped in labeling the plants and carried out some weeding, mulching and general titivating in anticipation of the event. During my time in Belgium I also visited other sites of great interest, such as Bokrijk Arboretum, Delabroye Nursery in France (fantastic epimediums here) and the private garden designed by the influential Belgian designer Jacques Wirtz.

Visiting the nursery of Thierry Delabroye, specialised in herbaceous perennials

Notes on the management of the woody plants collections The gardeners at Wespelaar have their own philosophy in terms of raising and establishing trees and shrubs. Long-living specimens need to create the best possible symbiotic relationship with the surrounding soil and elements, therefore the woody plants are preferably grown in-situ in the very early stages, with only few specimens purchased from trusted nurseries. One of the keys points here is that pot culture is reduced to the minimum. Instead, immediately after germination or rooting, the plants are subjected to a dynamic, rather unbound process of acclimatization, going through nursery trays, the outdoor raised beds and a large heeling-in area before the planting-out in the Arboretum. In all these steps, the local soil is used, keeping the use of specific growing media only for the fussiest growers. The disadvantages consist of a long growing timespan and a risk of failure given by the use of non-uniform and unsterile soil, as well as by the forced exposure to the elements. On the other hand, the advantages are numerous: apart from the obvious economic aspect, the long-term culture allows wild collected material to be gradually introduced into the collection. Moreover, greater knowledge and awareness can be gained on both the specific plants requirements and local growing conditions. The actual planting-out is carried out in a rather different way to the official RHS one. The planting holes I dug at Wespelaar were much smaller and shallower to the ones we usually see in UK; no double digging was carried out, nor blood fish and bone or other fertiliser were forked in. The theory behind it is that a too comfortable hole will replicate the unnatural pot culture, leading to plants that will boost their growth in the first stages, developing big branches and leaves while lacking an adequate root system. If the specimens struggle after planting, they are fed with manure for a couple of years, and then removed if still not performing well. Even if this system is inappropriate for domestic gardening or for the most valuable specimens, I think it is totally acceptable in the case of a large arboretum, as stronger plants will be grown in the longer term.

Stachyurus himalaicus

Finally, some consideration on the nature of the administration and management at Wespelaar Arboretum. I felt that all this arboricultural and horticultural free rein is possible for two main reasons. The first reason is related to the influence of the enlightened patronage of Philippe de Spoelberch, who started the arboretum in 1984 as an extension of his dendrological collections and donated to the Foundation Arboretum Wespelaar in 2007. Philippe continually backs up the staff, putting constant inputs in the day-to-day management. He also promotes expeditions for collecting species in the wild.

The playing-card-system I saw used at Wespelaar was his idea. This consists in marking the nursery plants with series of playing cards, so as to help the staff in identifying the plants and avoiding confusion; the playing cards are left on newly planted specimens and act as back-ups for checking and accessioning them.

Playing cards help the team in quickly identifying and accessioning the plants This example leads to the second reason of the independence of thought at Wespelaar. Such an anesthetic blotch would not be possible in a garden of the National Trust or English Heritage. Equally, the tendency to plant very young plants (or even seedlings, in some case) and to wait for them to establish would not be acceptable. Wespelaar is a Private Foundation and is open to the public only on Wednesdays and Saturdays. This is deliberate and gives the staff the chance to prioritize different tasks in accordance with the opening days and times. Labeling Correct labeling is crucial for properly identifying individual specimens within a plant collection. At Wespelaar and Herkenrode all the plants are individually accessioned but only the woody material is labelled. The exception is given in groups of herbaceous perennials that the arboretum is specializing in, such as some herbaceous Berberidaceae. Two different labels are put on each plant. The display label is a large and hard label, which is stuck in the ground and serves to the public for interpretation; it gives not only information on the plant’s family, botanical name and distribution, but also an indication of the parentage in the case of hybrids. The second label is perhaps the most important and consists of a rigid plastic band which is tied to the plant and serves for internal accessioning. Apart from showing the name of the plant and the eventual parentage, it contains the accession number, which is an alphanumeric code containing information on the date and place of acquisition of the particular plant. Both label types are white and engraved in white, so the dirtier they get, the more readable they become!

Sometimes geophytes are labelled too when present in masses in a border or a bed. The method is quite clever as the different species are grouped in a single label, so avoiding an unnecessary plethora of labels sticking out of the bare ground during the dormant season. This method can be certainly used not only in a specialised arboretum like Wespelaar, but also in many public gardens and private estates.

Different labels for different purposes Magnolia pollination Many of the today’s most-loved garden plants and crops are the result of long processes of human hybridization and selection; roses, citruses and cabbages, in the forms we know them, do not originate from nature. Equally, most of the variation in the genus Magnolia comes from the hybrids produced by gardeners and breeders over the last two centuries, combining and enhancing flower color, hardiness, fragrance, persistent foliage, and a range of mature sizes and habits. Many of the best selections are from Germany and the north-eastern United States, which offer ideal climates with less late frosts and shorter winters respectively. One of the most popular garden magnolias, Magnolia x soulangeana, is a man-made hybrid of M. lilliflora and M. denudata. The yellow flowering selections only appeared in the Seventies thanks to the work initiated with M. acuminata at the Brooklyn Botanic Garden. More recently, the reorganization of Michelia, Manglietia and to a lesser extent Parakmeria, Manglietiastrum, Pachylarnax into specific subgenera and sections within the genus Magnolia provides valuable insight and direction for plant breeders.

Magnolia dawsoniana ‘Valley Splendour’

Magnolia ‘Black Tulip’

One of the reasons why hybridizations have been so successful with this genus is because the hand pollination is so easy to carry out. Magnolias are monoecious plants, containing both male and female flowers on the same individual. To pollinate magnolias it is necessary to a pick a fully opened, male flower and gently brush it against a female counterpart, which should be still perfectly closed, so ensuring that no pollinators have been visited before; all the tepals are stripped away by hand and the pollen-covered stamens are brushed against the carpels of the female. It is a good practice to remove the flowers nearby, so avoiding the traffic of pollinators. Finally, the pollinated flower is bagged and labelled. The best time for carrying out hand pollination is late spring, preferably when there is no risk of late frosts, which is the real big threat, as it will avoid the formation of the fruit. If a fruit is produced later in the year, pollination has been successful and seeds can be collected and a new hybrid tested. Over the years, many interesting hybrids have been selected at Wespelaar. They are only named after years of observations and comparison, if showing exceptional qualities and are therefore worth commercializing.

Hand pollinating magnolias

For further research For those interested in magnolias, in the RHS Plantsman June 2015 is an interesting article of yellow magnolias by Koen Camelbeke, Curator at Wespelaar Arboretum, and Maurice Foster. This article, together with other excellent scientific publications on the dendrological collection at Wespelaar, can also be found here: http://www.arboretumwespelaar.be/EN/Publications_and_Downloads/ Other interesting links are: Delabroye Nursery - http://www.mytho-fleurs.com/les_vivaces_de_sandrine_et_thierry.htm Bokrijk Arboretum - http://www.bgci.org/garden.php?id=2354 Jacques Wirtz, prominent Belgian landscape architect - http://www.wirtznv.be/en/intro/ Also check past PGG journals (Jan 2014 and Jan 2015 editions) for other articles on the PGG study tours to the Belgian gardens and arboreta.

Magnolia stellata and myself at Bokrijk Arboretum