Answer: This type of space with a restricted root run, heat reflecting off a building and a narrow aboveground space does sound very difficult. Hollies are particularly sensitive to reflected heat during the winter, so that shrub will probably not be the answer. If you need a pencil shaped plant you might try one of the narrow cylindrical junipers instead; these plants are tolerant of heat and poor, dry soil. Another option would be to train vines to a trellis. The roses are probably suffering because they need a good rich evenly moist soil with plenty of organic matter added to do their best, and by your description that location is not on the type of soil they require. Instead, you might try a trumpet vine (Campsis radicans) which is very vigorous and should be able to grow in that location; it will need an extremely sturdy trellis and an annual trim in late winter. Another possibility since you need drama in that location would be to train an espalier on that wall, possibly a pyracantha. Before planting, be sure to loosen the native soil as deep as you can and add copious amounts of organic matter such as compost or well aged stable manure and bedding to the soil, this is a better amendment than trying to add topsoil (which comes in varying quality and make-up). Then make sure you use a good organic mulch year round to help hold soil moisture and keep it cool as well as feed the soil as it breaks down.Yet another option might be to plant a groundcover effect of sedums or dianthus or similar tough sun loving perennial and then use large planter hung on the wall, perhaps in tandem with some architectural scale ornaments, a mural, or some other "dramatic" treatment. If you use a planter (s) make sure to add water holding polymer to the soil mix.
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