Yes, very large and not only that, they don't give a crop for a few years after planting.

There now dwarf walnut trees that can be pruned to keep them even smaller and they will produce a crop in a much shorter time than the old varieties. So if they are similar to Juglans regia 'Broadview' then perhaps not a problem.

Another thing about walnut trees is that they produce a toxin called juglone which inhibits the growth of many many other plants. Very few things will thrive under a walnut tree, even long after it is removed. Black Walnut is most offensive, but English Walnut still produces it.

All the talk in gardening circles is about juglone, but the walnut tree also produces many other chemicals that probably also exhibit allelopathic properties. These include compounds like flavonoids, terpenoids, alkaloids, steroids, carbohydrates, and amino acids, with mixtures of different compounds sometimes having a greater allelopathic effect than individual compounds alone.

https://www.gardenmyths.com/walnuts-juglone-allelopathy/

I have never heard that before, I look after a herbaceous border which half runs beneath an enormous walnut tree, on the other side of tree there are Rhodis and azaleas all thriving and I have a large compost area full of rotting compost leaves from last autumn which are full of golden willow cuttings that have taken really well.

Your neighbour need not worry about the size of the trees. They are very slow growing.

Bathgate is absolutely correct. Walnuts produce a chemical from its roots called Juglone. It inhibits the growth and competition from surrounding plants but there are some plants that will tolerate it.

Julien - the link provided by Bathgate is an interesting read, but in general in the UK, most plants do seem to be perfectly happy growing near or even under walnut trees, well, the type we plant in the UK anyway

Thanks Jimmy. Julien. take time to read the article. I said 'many' not 'all' and black walnut is more offensive than other types. It was just an interesting note.

Thanks for the info Bathgate, very interesting, I was not disputing your point, but when you stated very few things will grow under a walnut it’s only fair that I point out that clearly many plants do grow beneath walnut trees and this is based on observations over many years of gardening and this advice is important for other people to know.

On the upside, friends living in France tell me they keep mosquitoes away!

I know you weren't disputing my point Julien and it's ok if you were. I don't mind if somebody challenges me because I'm definitely wrong about a lot of things a whole bunch of times. I try to at least do a little research before I open my mouth, lol. If you can prove your point then you might just win me over. I think it's amazing that some plants can thrive in such a toxic environment. Rhododendrons & Azaleas do prefer an acidic environment so I can see how they would grow there. Black walnuts produce a stronger toxin than the English Walnuts.