Answer: Cyathea cooperi, the Austrailian (or Tasmanian) Tree Fern should thrive in full sun to partial shade, in average to rich garden soil when watered regularly during the growing season. These are fast growing trees under the right circumstances and can reach 20' tall, spreading about 12' wide. The blackening fronds indicate a stressful condition; too much water, not enough sunshine or even a fungal disease.
Instead of relying on a long-distance diagnosis, why not take a sample of the problem to your local Cooperative Extension office? They can provide an accurate diagnosis and suggest control measures. Phone (805) 645-1451 for office hours.
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