Posted: 02/02/2017 at 18:17
Many thanks for all the thoughtful responses. We have been investigating the problem online, but also, (inspired by Pansyface - thank you again!) we have looked for anything that might have heightened the possibility of rot in the past few years.
Astonishingly, we found out yesterday that the disappearance of my mother's bulbs could be the result of a new housing estate being built just above my mother's house on the high ridge where she lives. This came to light when she called the water authority to investigate a different problem, a very worrying noise of gushing water, which she had assumed was a broken pipe. An investigative engineer came out, and advised that it sounded more like a gushing stream. The probable source of this new stream seems likely to be inadequate drainage provided for the new estate, the water having found a new course, rushing away on the outside of the existent pipework. This new stream is, according to the engineer, either passing very close by my mother's foundations, or under her house, possibly emerging and gathering on the other side, in her previously well drained garden! We are quite stunned. According to the engineer, the problem(s) caused, which may involve structural repairs, can be solved once the entire road has been closed, taken up, and a new and adequate system installed
My advice to anyone who has something big and unexpected happen in their garden is not to ignore it, but to look out for changes in the nearby landscape in case there is a causal link!!!
I recounted all your suggestions to my mother, and she wants me to pass on her thanks to all for sharing your valuable experience and information