Posted: 08/09/2016 at 07:31
Don't cut them back yet! They look old and tired and dry to me but not dead. Allow them to die back in their own time and then cut off and compost the top growth. Next year, feed your border, mulch in spring and keep an eye on watering in dry periods. In my experience, aster will grow perfectly well with JA's though you may have to stop invasion attempts. However, slugs love aster and may have eaten all the emerging shoots so have a look for their remains - the aster, not slugs! - before you draw any conclusions.