I have a bunch of Grace Ward Lithodora. They have been in the ground over a year, they were looking good but now turning black. What can I do to stop this?
Without knowing anything about the growing conditions, I'll hazard the guess that it's because of too much water. I think that if you pull up one of the sick plants, you'll find root rot.
Plenty of morning sun and drier soil conditions can help. Lithodora re-planted in the same site probably won't do well because fungal spores will remain in the soil unless the soil is replaced. However, treating the soil with fungicide and lowering the pH below 5.0 might help. Using a sulfur-based fungicide would lower the pH and treat fungus, too.
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