Growing Walnuts

Does anyone know what I musn't grow near or in the same large pot as an English walnut tree?

My mum has a 20 litre pot for the walnut tree in our garden in North London - she has planted around the tree Antirhinum, but we're worried that it may not good together... as I've heard Walnuts are pretty fussy with who they share their ground with.

I bought the walnut tree last week at Amazon.co.uk at 3ft tall.

 

For starters I'm not sure a walnut tree would do well in a container, but I bet the Bonsai people would say otherwise.:D

Having said that, I dont think it would like having any other plant growing in the same pot due to the loss of root room and nutrient.
And I have heard that walnuts secrete a substance from their roots that poisons other plants in the area.:skp:

True or not I dont know, cant say I noticed it when I had a 20ft one in my garden, and that was only 15yrs old when I decided it had to go.:D

 

I roughly planted a walnut (shop brought) shell included, in a 12" round pot, about 3.5 years ago, just to see what would happen......

Its about 5' tall now!!