Answer: Cedar is an aromatic wood, and it has long been used to repel moths and other pests in the home. But I don't think cedar has any poisonous effect on other plants. More likely, during the drought we had last summer, the large, vigorous tree sapped all the moisture from the soil, leaving the hosta without enough to survive. This often happens when gardeners try to grow plants under large trees. Some of my hostas seccumbed in the dry heat last summer, even though they were in shade, and I watered them fairly regularly.
You may want to try growing more drought-tolerant plants under your trees instead, such as lavender or dwarf daylilies. Both will need regular watering until they become established, but after that, they should be able to hold their own. Good luck!
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