When they are that yellow they are either poorly planted, in that I mean, soil not properly dug and loosened, or the soil around the plant has become compacted and there has been water-logging. This alone will stop nutrients getting into your roots. Two feeds will not see results straight away. If it doesn't improve after one and a half months, I think you will need to look into the roots and re-plant again making sure the soil is loosened and it drains properly. The area looks very congested, bear in mind, these shrubs will widen as well as grow tall once established. I'm not sure it is in an ideal spot.
Hi when planted the holes were dug deep and wide enough to accommodate root ball and a bit of fish blood and bone added at the Same time and well watered. I put some mulch/bark all along base of plants .Noticed yellowing early this year.
Keep up with the feeding then and wait a bit longer. You mentioned you have not checked your soil type. Is it heavy and clay like? In some instances, you may need to feed it magnesium and iron, if the soil is very alkaline, which is another reason for yellow leaves. But generally, these shrubs are quite tolerant with soils. It's just the first year once planted, the soil needs to be well prepared for them to put down roots.
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Yes my soil is heavy and clay, I will keep an eye on them and maybe remove the worst one and look at giving them magnisium and iron. Thank you.