Thuja Smaragd also known as emerald arborvitae, prefer a sunny and an open area with well-drained and moist soil. The conifers have the ability to tolerate a wide range of conditions and soils. During the cold months, this tree keeps its emerald green color. To give the trees a full growing season plant them in early Spring after the danger of frost passes, this will establish the roots of the tree before winter arrives. To get the satisfactory results, fertilize them with a slow release of long-term fertilizer in early spring and trim when required to give them a better shape.