Answer: Unfortunately, based on your description, I am unable to tell you what is happening to the yews. I would suggest you work with your local county extension to try to troubleshoot the problem. In my experience, a situation like this can sometimes be soil related, perhaps there is some sort of unusual soil situation in the area where they are planted. For example, along a foundation where the soil was disturbed during the building process there can be a mixture of soils, or there may be something buried below ground that is causing problems with root development -- possibly something as unusual as an old black walnut tree root, or there might be a soil-borne disease problem. Sometimes it takes some detective work to figure it out. I'm sorry I can't be more specific for you.
Q&A Library Searching Tips