I wondered if anyone had any experience with how european hornbeam co-exists with walnut? I have not been able to find any info on the effect of juglone on european hornbeam. I suspect that UK gardeners use hornbeam ornamentally far more than we in the US and thus might have some observations to offer.
Trouble is, although Hornbeam is fairly common, we don't grow so much Black Walnut Juglans nigra (which is likely what you have, and is a much worse juglone producer than Common Walnut J. regia). The closest I've seen the two planted is about 100m apart, on either side of a main road. Not too useful for juglone effect studies!
I've just caught up with this thread. Walnuts produce juglone, a chemical from the roots which is poisonous to a lot of other plants. A great survival mechanism from the walnuts point of view if not from the gardeners!
There are other plants that do the same thing, too. The common rododendron is notorious for it which is why it has become a real weed in parts of the UK. I notice that not many other plants thrive around some eucalyptii so it may be the case there as well.
All one can do is to keep the poisonous plants away from other species.
