Answer: It is difficult to make specific plant suggestions long distance. Your choice will depend partly on personal taste and partly on the growing conditions where you are planting. For instance, hostas need shade so if your site is very sunny they will not do well. Junipers require full sun (at least six hours of sun including the hour of noon) to stay healthy and grow well. Junipers require a well drained soil while the Itea will do better in soil that is evenly moist.
Also, although it seems like a big space now while it is empty, once your plants begin to grow it will fill in quickly. So try to keep in mind the mature sizes of the plants you are considering. For example, Itea "Little Henry" grows to about three feet tall and three feet wide, and Itea "Henry's Garnet" grows about six feet tall and wider than that.
Finally, all plants require some routine care. After planting, they will need watering if it does not rain enough to keep the soil evenly moist while they are becoming rooted and established which takes a year or two. They will need mulching and weeding as well.
In such a small space, you may find it looks better to limit yourself to a fairly short list of plants. You might use several junipers (all the same kind)to one end so they will not be shaded by the Itea, several of the Itea clustered together, and front that with some spring blooming daffodils, daylilies for summer bloom and some sedums for later season color. You can arrange these informally or formally, depending on the style of your other landscaping and the design of the wall and fountain.
Your local professionally trained nursery staff should be able to help you identify plants that will grow well in the location you have in mind as well as meet your overall design goals. In the meantime, I hope this helps you get started with your planning.
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