Laurels stopped growing

Several years ago, I choose the cherry laurels for a quick hedge 30 plants 2ft feet apart in tiny pots approx 1ft in height. Using all my gardening experience they were planted in a fashion not dissimilar to a rice paddy farmer. (I laid down a cheap membrane and mulched)Needless to say in the next 24 months I was rewarded with nothing. I didnt lose any plants. In places they have reached 5ft (please see the pictures)some are still only 2ft and all suffered with Mildew and a little shot hole. The grounds clay and the meter says the PH is 7. Would a little Epsom salt help? (Magnesium sulphate) Should it be sprayed directly onto the leaf or poured into the ground I've recently thrown some bone meal down. Should I mulch again I've weeded around the base.