Horticultural report on a fortnight work experience at Arboretum Wespelaar and the linked Herkenrode Gardens.

1. 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

2. 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!

3. 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

4. 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.

5. 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!

6. 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’

7. 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

8. 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