Laurel Hedge failing

Niall Brady asked 4 years ago
I have a laurel hedge which was planted in June 2010. The ground in which it is planted is a heavy clay soil type but I have a land drain running along both sides of the hedge and it is also planted up on a mound of soil which I got from digging the land drain so it is of the same type. This mound is also covered with weed block netting and I have wind block netting around the hedge also. Initially it done very well but this last few years it has gone backwards. The leaves are yellow in colour and the fall off quite easily. I have noticed on one area particularly that the leaves have gone soft and are drooping down. I have put chicken manure pellets around the base of some plants which does work in the short term but then the go back the same again. A friend of mine who works with the forestry seen it and said I need to put down “muriate of potash” as it seems to be lacking some nutrients. He also said that the cure can be worse than the disease so that has me worried that I could do more damage plus I am finding it hard to find a place that stacks it. So is there something similar to muriate of potash but would be safer to use?