Answer: You've identified the two most likely causes for failure of perennials to thrive when planted under trees - they must compete with tree roots for water and nutrients (the trees usually win!) and the shade can be too dense for some plants. Daffodils should be happy under your hollies, and other choices include Coral Bells (Heuchera) Irises (Iris) Nepeta (Nepeta subsessilis) Penstemons (Penstemon) Sword Fern (Polystichum munitum) and California Blue-Eyed Grass (Sisyrinchium bellum) You might also consider Heavenly Bamboo (Nandina domestica) Cotoneaster, Hypericum, Lamium, and Viola. Many annuals will be quite happy under your hollies. Because they have short lifecycles you'll need to replace them often, but they can provide lots of color from spring through autumn. I'd stay away from sedums - they require full sunshine for best growth. Hope the above suggestions help you perk up the planting area beneath your hollies.
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