Answer: Outdoor planters can be difficult to plant because the plants' roots are not as well insulated as they would be in the ground, the potting soil tends to deteriorate over time, and there is reflected heat and sun coming off the building. In my experience, you did exceptionally well to keep the roses going for more than a year -- in most cases the plants in planters do not make it for that long. You might try dwarf Alberta spruce, but if you do, keep a very close watch on them for mites and be prepared to treat them at the first sign. Your local professionally trained nursery staff may have other suggestions based on a more detailed understanding of the growing conditions in the planter (sun, shade, wind exposure and so on) and your overall design goals.
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