By Redspan
United Kingdom 
My neighbour has a mature cypress tree in his back garden and it overhangs into mine, over a border bed. It's protected by a tree preservation order so I can't cut off any branches (apart from storm damage).
I've used a soil tester and it's clear that the soil is very alkaline, which probably explains why everything I've planted has either died or failed to grow.
Would English Laurel be able to cope? I would like to plant it to create a 7ft hedge along the border, but having lost money on previous planting I don't want to shell out again only to see them wither and die in the alkaline soil.
If not laurel, can you suggest anything else that can be used to create a hedge? It needs to be 7ft high for screening.
Thanks in advance.
1 Jun, 2016
Answers
Loads of things grow in alkaline soil, shouldn't be a problem. The shade and soil impoverishment from the tree roots are more likely to affect your hedge.
1 Jun, 2016
I used a kit from Garsons - took a sample of soil from 5 inches down, dried it out, added it to the test tube, and topped up with water. Left it a while and it went dark green so according to the chart is alkaline.
The border is right under the tree and the sample was from about 5 ft from the trunk. The lower branches are about 8 feet up.
2 Jun, 2016
I too would be surprised to find very alkaline soil beneath a mature cypress. I would expect it to be acidic.
2 Jun, 2016
Well, I doubt that soil pH is a problem, frankly. Were the conditions so alkaline, the cypress itself would be showing signs of ill health. Relatively inexpensive soil pH testing kits aren't renowned for their accuracy, and a highly alkaline soil five feet from a large cypress seems unlikely, so I'd stop worrying about soil pH, given there are other, much more obvious causes for new plants dying.
It sounds as if you want to plant under the canopy of the tree, and well within its dripline. You haven't said how tall the tree is, but if the lowest branches are about eight feet from the ground, then it's likely at least twenty feet high. Anything you plant under the canopy is likely not to do well - the fibrous roots of the cypress will suck moisture from the soil, and five feet from the trunk, there are likely to be many small roots. These are inhospitable conditions for new plants because they're unable to compete and probably can't develop their own extensive root system, given the competition.
It would be useful to see pohotos of the area you want to plant up, but it sounds as if you need to consider planting much further out from the canopy, and certainly more than 8 feet from the trunk.
2 Jun, 2016
What ph reading did you get when you tested the soil? I'd be surprised if it was highly alkaline, with a cypress growing healthily nearby, what kind of test kit did you use, or was it a laboratory test?
How close is the trunk of the tree to where you want to plant a hedge, and would the hedge be growing inside the dripline of the tree, in other words, underneath the cypress foliage? A hint as to the height of the cypress would be helpful too.
1 Jun, 2016