By Davbeau
United Kingdom 
We live in a modern building on a busy road in London. Box hedges have been planted along the front of the building - partly aesthetic and partly for some privacy for ground floor dwellers. But the box hedges keep dying. This is the explanation from the freeholder responsible for their upkeep:
"The problem is that the planting area is not big enough for the size of shrubs. The ones that are in now were put in in early 2016, and these replaced smaller one which were also struggling. The planting area is so shallow that the shrubs could not be planted low enough - there is concrete at the bottom which means there is not enough soil. If we plant anything living we will have this problem again."
This was the view of one of the residents who saw them putting the plants in:
"I was actually present when the workers came to plant the larger box plants & saw they were not bedded in properly so unsurprisingly the roots had nothing to grow into and may be the reason why so many died? Box plants are very hardy & perfectly able to survive in urban areas..."
Now they are suggesting putting fake plants instead. I'm worried that will look really bad.
Is the excuse about the area being too shallow for the roots valid? If so can anything be done to help the plants? Are there any good alternative plants that might fare much better in this situation? That require less depth for their roots?
1 Feb, 2018
Answers
I seem to remember you asking this before under a different name with a photo, and that the answer was that with concrete under the soil it is probably not deep enough to support a box hedge or possibly any other kind of shrub. You would need to break up the concrete to give the roots somewhere to go down, and to ensure drainage. Box is one of the shrubs recommended for dry shallow soils so if that doesn't survive its unlikely other shrubs would live long term.
If you are sure that the plants were not planted properly you could challenge the firm who planted them to see if replacements properly planted would survive but in any case with dry shallow soil they would need to be kept very well trimmed so that there is not a large area of leaf to be supported, so in;ess the shallow soil problem is addressed they would not get tall enough to give privacy. for the ground floor windows.
I can't remember what suggestions were offered for alternatives - perhaps you can recall what was said then.
1 Feb, 2018
The best solution may be to build large (70 cm wide by 70 cm deep) insulated troughs, with trellises and evergreen vines. The critical requirement for that would be provision for drainage. I don't imagine that the local council will be amused by brownish water running across the adjoining sidewalk! Shrubs will also grow in such troughs, but will be slower to develop the needed height and coverage. One nice extra is the possibility for decorative faces to the troughs, and/or seasonal flowers spotted between the vines.
2 Feb, 2018
Bamboo grows well in troughs or tall pots - a neighbour has them in front of their window for privacy and they still let the light through.
2 Feb, 2018
Just don't forget to water them in dry periods. If drought stressed, they drop their leaves, and may take months to recover. Heavy feeders, too.
3 Feb, 2018
Thats a good idea.
3 Feb, 2018
welcome to GoY Davbeau.
Exactly how deep is the soil that you have? Without knowing that it would be difficult to suggest anything. But a shallow soil onto concrete isn't good. Box is usually a good plant [unless it gets box blight].
Could you add a photo to your question so we can get a better idea of the situation?
Fake plants will soon look dirty and unappealing. It would be more cost effective if the owner of the freehold did remedial work to correct the problem.
Sorry not necessarily the answer you were after.
1 Feb, 2018