We have bought a house that has a lovely box knott garden. During the months since we moved in some of the box trees have started to turn yellow and now many of them are completely yellow. As yet the leaves are not dropping off.

Picture of the hedges

We were told that it was maybe because the soil was too damp and indeed the box's are planted in soil which has a very tight weedproof membrane and then the blue slate on top. We tried cutting the membrane back about a foot fron the edge so the box were not totally surrounded by membrane but this doesnt seem to have helped.

Interestingly many of the plants are flourishing and odd ones in the middle of yellow ones are green. We have whole sections that are still green and much taller and stronger than the yellow ones.

Does anyone know what else we should try.
We have bought a house that has a lovely box knott garden. During the months since we moved in some of the box trees have started to turn yellow and now many of them are completely yellow. As yet the leaves are not dropping off.

Picture of the hedges

We were told that it was maybe because the soil was too damp and indeed the box's are planted in soil which has a very tight weedproof membrane and then the blue slate on top. We tried cutting the membrane back about a foot fron the edge so the box were not totally surrounded by membrane but this doesnt seem to have helped.

Interestingly many of the plants are flourishing and odd ones in the middle of yellow ones are green. You cant see from this picture but we have whole sections that are still green and much taller and stronger than the yellow ones.

Does anyone know what else we should try.