Answer: Besides the litter they drop, the chief problems when planting under cedar trees are deep shade and thick mats of relatively shallow roots that crowd out others and compete unfavorably for water. The severity of the problems depends somewhat on the size of the cedar, so you'll have to watch your plants carefully and rescue them if the competition is too great.
With that said, I'd concentrate on using plants that tolerate dry shade. Some suggestions include Bergenia, Erigeron (Mexican daisy), Iris, Nepeta (catmint), Penstemon, Clivia, Senecio, Heuchera (coral bells), Hosta, Impatiens, Lily, Lobelia, and Caladium bicolor. Vinca minor makes a nice groundcover beneath trees and isn't as aggressive as ivy.
Good luck with your renovation project!
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