I have a slightly different, but closely related issue, that I would like help with. I bought and planted a native (to the UK where I live) rowan tree, I then got sent another much smaller tree by the same company and they let me keep both. Our garden is tiny (we live right in the center of London) and didn't have enough space for another tree and the other plants we had planted, so I gave it to our neighbours. They then planted it right next to the garden fence within a meter of our tree, I did mention they were probably too close, but our neighbours are not interested in gardening and its never been moved.Will it cause any problems being so close? Ours is the larger tree and I'm not too bothered if it just stunts the growth, but I would be slightly put out if it kills ours or so some other negative effect.