Hybrid walnuts show promise

Walnut trees are much-loved by many growers who recognise their fast growth and high value.  However, both the common (often called English) walnut Juglans regia and black walnut J. nigra are quite particular in terms of optimal growing conditions. Hybrid walnuts provide an exciting alternative.

Many trees will naturally hybridise in the wild with similar species in the same family: examples include larch, lime and poplar.  It is also possible to encourage and control hybridisation through tree breeding programmes.  Hybrid species tend to have greater than either of their parents, and may be more tolerant to a wider range of conditions.

Across Europe several varieties of walnut  hybrids have been bred and made commercially available. They include both Juglans nigra x J. regia (e.g. NG23, NG38) and J. major x J. regia (e.g. MJ209) crosses, all of which are vigorous and have good form.  Hybrids planted into existing woodlands in continental Europe have grown very well, generally have good apical dominance and fewer branches than either species.

There have been limited plantings of walnut hybrids in the UK.  I planted some silvicultural trials, with the Northmoor Trust in the early 2000s.  In 2003 I established a hybrid varietal trial with the Northmoor Trust.  The hybrid walnuts were planted in a mixture with alder (Alnus glutinosa), silver birch (Betula pendula) and wild cherry (Prunus avium).  The alder, as a nitrogen-fixing nurse tree, was included to provide a natural fertilising effect for the walnut.

walnut hybrid growth
Five year height growth (cm) of walnut hybrids

As the graph shows, once that the walnut trees had become established, growth was very good.  The NG38 trees in particular grew phenomenally well; being over 3 metres tall by year 5.  One individual NG38 tree grew 2.68m (over 8’6″) during the fifth growing season alone!

Hybrid walnuts have the potential to be a fast-growing home-grown hardwood alternative to timber imported from far away.  They do not have the dark heartwood so prized by furniture makers but hybrid walnut timber is easy to work. can be sliced for veneer and is easily stained.  Lastly yet importantly, they are likely to benefit from projected climate change.

I recently published an article on this:   Clark, J., and Hemery, G. ( 2010 ) Walnut hybrids in the UK: fast growing quality hardwoods. Quarterly Journal of Forestry. 104, 1, 43-46. Read the full article at Forestry Horizons.

Gabriel Hemery

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5 thoughts on “Hybrid walnuts show promise

  1. Hi Gabriel
    Very interesting to hear about the hybrid walnuts. How frost tolerant are they? And where do you buy them and how much? I may have some clients who may be interested in planting.
    Thanks
    Robin

    1. Hi Robin
      Thanks for your comments. Hybrid walnuts have the same winter cold tolerance as their parent species. In terms of potential to damage from late spring frosts, which I presume is what you’re refering to, they tend to be fairly late-leafing so are quite suitable. The same rules would apply re site selection in terms of avoiding frost hollows.
      I was for some time involved in the Walnut Tree Company when we suppled hybrid walnuts to the British market. You could try their website: http://www.WalnutTrees.co.uk. If they are no longer supplying, you may need to approach some Frence nurseries direct.
      Hope this helps
      Gabriel

  2. Hi Gabriel,

    Are there any differences in leafing out times between the J.nigra x regia hybrids and J.nigra? Am I right in thinking the hybrids might be later?

    1. Hi Michael – thanks for your question. I assume you are referring to flushing in Spring? Yes generally the hybrids are later and in some cases may have been selected to be late-flushing. Timings will vary between the different hybrids too course, but I wouldn’t be able to tell you any details.
      Gabriel Hemery

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