Posted: 23/05/2013 at 19:46
Thanks everyone for your replies. The wall is about three feet high and has gravel at the top. The gravel area does have a wide border at the back, against the fence and lots of things are growing there quite happily. I have been digging lots of compost into the borders, but the area under the gravel is, I know, compacted heavy clay with lots of large stones in it. Digging that lot up is not an option - not as young as I used to be!! . Thanks Verdun for the hydrangea suggestion - didn't realise it would grow in very wet soil, and the fern suggestion is definitely an option. Thanks again everyone.