Answer: It can be very difficult to plant under evergreen trees because the trees prevent rain from reaching the ground, their roots steal moisture and nutrients fromt he soil and the trees cast deep shade as well. In many cases, it is better to leave the natural carpet of fallen needles beneath the tree without trying to grow anything. A cedar mulch would be fine; keep it no deeper than two to three inches thick and do not allow it to touch the trunk of the tree. If you would like flowering annuals, you might consider using a large container or two planted with colorful impatiens or other shade tolerant flowers. If you prefer perennials, you might try one of the hardier Hedera helix such as "Baltica" (an evergreen groundcover) or possibly epimedium (deciduous, very small flowers). To plant, you will probably need to dig individual planting holes in between the tree roots, work in some compost, plant, water thoroughly and then keep the soil evenly moist while it becomes established. Take care not to damage too many tree roots when you plant. I hope this gives you some ideas.
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