Hebes going yellow

Hi there, I have some dwarf hebes planted up my driveway and most of them have gone a very light green, bordering on yellow. When we planted them, we noticed there was a lot of white clumps in the soil which we think could be limestone from the driveway preparation, some 20 years ago. The area where there are a couple of hebes that have grown well and are still dark green, had far less of the white clumps in the soil. I had one hebe die completely within a few weeks of being planted so I just thought that was bad luck…. however I have since noticed this yellowing and no new growth of the remaining hebes (except for the couple closest to the house end of the driveway where there wasn’t as much of this limestone-looking stuff). I had put the lack of growth down to it being winter, but since there are a couple which are way bigger and darker green than the others, when they started off the same, I’m thinking it is to do with the soil.
Is there something I could spray on the plants to fix the soil so that my hebes can get better and grow normally? Or something else I could try?
Thanks for your help!
Jo