Clonal Propagation of Oaks

Oak Open Day 2013 - Belgium

Clonal Propagation of Oaks

 

On Sunday, 22nd of September 2013, about 30 oak enthusiasts gathered at Pavia Nurseries in Deerlijk, Belgium for an Oak Open Day that was to be devoted to clonal propagation (mainly grafting) of oaks. Our hosts were Dirk and Katrien Benoit-Vercruysse, owners of the nursery. Dirk was a member of the Board of the IOS until 2012 and is a longtime member of the Society.  

We had a diverse group of attendees coming from six different countries of the European Union: France, Germany, Italy, Luxemburg, the Netherlands and of course Belgium. Quite a few were nurserymen or garden designers. All were oak enthusiasts. 

Eike Jablonski, past President of the IOS and oak expert, was present as well as Jan De Langhe, author of an identification key of oaks in cultivation. This key can be found on the website of Arboretum Wespelaar.

Jean-Louis Hélardot, author of the excellent website Oaks of the World had also come from France, as well as Stéphane Brâme, one of the early members and founders of the IOS, and many others including Gert Fortgens from the Trompenburg Tuinen & Arboretum, our current secretary, who had come from Rotterdam and Dirk De Meyere from the National Botanical Garden of Belgium.

Grafting: extending the plantsman’s palette

The morning of our Oak Open Day was devoted to a presentation by Dirk Benoit about propagating oaks by grafting. This propagation technique has been criticized by many in recent years, actually ever since wild-collected plants have become the craze. And personally, I believe firmly that oak collectors with enough space should favor oaks from wild origin. Dirk Benoit himself has been collecting acorns (and scions) in many different parts of the world. Add to this graft incompatibility, especially delayed incompatibility, which I find particularly annoying (an understatement) and you have a propagation technique that has had bad press in recent years. 

Yet, there are many excellent reasons to graft oaks. 

A first excellent reason (for the “serious” oak collector) is when you find an oak in the wild that you would like to collect and there are no acorns. That is what Dirk Benoit did in Mexico in 2009 when we saw Quercus urbanii in the wild.  

Quercus urbanii (grafted) (Photo: Dirk Benoit)

Further, with natural hybridization, one can never be sure that we shall have a specimen typical of the species collected. 

Other reasons were cited and discussed. Rootstock choice might improve the hardiness of an otherwise tender species or allow planting in unfavorable soil conditions (high pH, wet boggy soil…).   

There are simple horticultural reasons for grafting oaks: selections for

  • Habit: Q. robur ‘Fastigiata Group’ comes more or less true from seed, but try seedlings of this oak in street plantings: a disappointment. In some cases, uniformity is needed.
  • Leaf Color: the old Belgian cultivar, Q. robur ‘Concordia’ was mentioned and shown in the presentation.
  • Autumn Color: Q. coccinea ‘Splendens’ was selected in Europe for its autumn colors because that species does not color well in Western Europe contrary to in its natural range.

Finally, we discussed the propagation of F1 hybrids, natural hybrids in many cases, or trees used for mast production. 

Eike Jablonski mentioned that in Germany, clones of Q. robur and Q. petraea are propagated by cuttings in industrial quantities for use in sylviculture.

The morning was concluded by a quick visit to the greenhouse where the Master demonstrates his grafting skills. Dirk also showed us his “hot-pipe callusing unit.” Pavia produces 20,000 grafted oaks annually. 

Dirk Benoit demonstrating grafting techniques

Before lunch, we visited yet another greenhouse with a wonderful display of a diverse assortment of oaks, all grafted. Several plants illustrated all the reasons given for grafting oaks: Q. tomentella (improved hardiness), Q. ×bebbiana (character preservation of the F1 hybrid). 

Q. ×bebbiana

In front of (and around) the greenhouse, we saw Q. ‘Chimney Fire’ (autumn color and habit), a seedling of the Riverbank Lodge Q. ×warei in Petersburg selected by Guy Sternberg, Q. × bimundorum ‘Crimschmidt’, an excellent columnar selection of Q. alba × Q. robur, and another hybrid named Q. ×schuettei, a hybrid between Q. bicolor and Q. macrocarpa, which strangely has some similarities with Q. pyrenaica.

Q. ×schuettei, a hybrid between Q. bicolor and Q. macrocarpa

Digression: I also spotted a few specimens of Sorbus harrowiana, a very beautiful rowan, not fully hardy in Belgium and several Sorbus gonggashanica, an apomict species introduced by Roy Lancaster. I wonder in this case if it makes sense to graft such a plant that can be cloned from seed.

We then had lunch in the garden of our hosts. Some had brought acorns, chestnuts and samaras and a seed give-away booth was dressed during lunch (pictures in this blog post)

Lunch in the garden

Nursery Fields

After lunch, we were off to the fields. We walked through rows of well-maintained nursery plants. We came across this interesting columnar tree, Q. ×bimundorum 'Crimschmidt', that I would like to see in the streets of Brussels.

Q. ×bimundorum 'Crimschmidt' in the nursery

In the field where Dirk keeps his mother plants, I spotted a good Q. grisea named 'Agatha Long' that does not appear in Dirk’s catalogue. 

Q. grisea 'Agatha Long'

We finished our walk in a field where one finds other plants than oaks. One particularly attracted my attention. It was a lime, Tilia henryana. The species was discovered by Augustine Henry in the Chinese province of Hupeh and is believed to have been introduced by Ernest Wilson. This tree is remarkable for its finely toothed leaves. The specimen at Pavia was selected by Dirk Benoit and Philippe de Spoelberch at the Arnold Arboretum in 1997 and later named ‘Arnold Select’.

Tilia henryana ‘Arnold Select’

The day closed in the nursery with the display of young grafted plants. Some stayed late to choose plants to take home (although not all plants displayed are for sale due to very limited quantities). I know which one I would choose if I still had a garden to plant it in and that is a nice velvety specimen of Q. dentata subsp. yunnanensis.

 Q. dentata subsp.  yunnanensis with the hands of Gert Fortgens

Pavia has about 160 oaks and oak cultivars for sale, but many more in its collection of “mother plants.”

I met Dirk for the first time during a trip in the Fall of 1997 in New England. I had never visited his nursery in Belgium until this 22nd of September. For some reason, it was never the right time. I am glad I did now. This is a great place to find interesting oaks and Dirk is a great and keen plantsman.

A shortened version of this write-up will be included in Oak News & Notes, the newsletter of the IOS. Eike Jablonski will write an account of the Oak Open Day for the IOS Journal.

Oak Open Days are IOS events open to any person interested in oaks, members of the Society and non-members alike. Check our calendar of events for future such events.

All photos by the author, except when otherwise mentioned.

Hannah and her grandfather