Posted: 27/07/2015 at 19:43
PoddingtonP - neighbour and I are having her elm felled very shortly as it's canopy causes darkness in both gardens - but worse for me, the roots from the tree are under my garden stretching about 15-20 foot counting the hairy subsidiary roots. This is why I have a 20ft area where all my shrubs consistently die off - caused by shade, by the tree sucking up the moisture - but mostly because the roots turned out to be fairly shallow under my soil - from a foot deep onwards. The roots were also working their way upwards over the years coming to almost the surface. So my shrubs which were thriving 4 years ago gradually got weaker, were never lush, growth was stunted, and they shrivelled up. For some stupid reason - I had never noticed the roots of the tree gradually working their way up nearer the surface of the soil as the years passed.
Our tree surgeon is felling the tree as it has become host to repetitions of scale, swarms of flies and all kinds of nasty beasties and our gardens are damp and dark due to the tree canopy - as well as the drip on the plants below from the canopy. However, because we live in town flats with limited entrance to the back gardens, a root remover and grinder cannot be brought in to the area - so we are being left with a stump and the roots in situ. So this is a problem for me - being stuck with those roots underground. (Yes, I've thought about digging down and attacking them with my saw - but don't have the energy.). So I am stuck with the fact that nothing will grow there longer than something very shallowly rooted - so I am currently working out what to do with this area to make it both productive and attractive. Sorry to go off topic a little. But I think you should have a dig down in your area...or hammer a pointed pole down in different places - and see if you have root obstruction which may be causing problems for your shrubs at the roots.
I dug out a Pieris Forest Flame Yesterday - took an hour simply because it transpired the elm tree roots had grown larger around the roots of the Pieris and literally crushed the Pieris roots in between its own roots. It hadn't occurred to me that this might be what was killing off my shrubs slowly over only 4 years.
My situation here may of course be totally irrelevant to yours as you say the sycamores are north of your planted area so they are maybe some distance away whereby roots would not be a problem at all.