Answer: Since these are raised planters, they will tend to dry out quickly, so make sure you use a good well draining but humus-rich planting mix in them. You might also consider using a water holding polymer product and possibly even install a high efficiency watering system and timer since this is easiest to do at the construction phase.
Having said that, for perennials you could try an assortment of perennial hostas in different foliage sizes, shapes and colors, perhaps along with annuals such as impatiens and caladiums for extra color.
If the planters are large, you could also consider dwarf nandina shrubs to add some winter height and seasonal fall color, or for evergreen foliage in a variety of colors, consider Euonymus fortunei plants which will grow as small shrubs or, in proximity to a support, will also climb.
I hope this gives you some ideas. Your local county extension and professional nursery personnel may also have some suggestions based on a more specific description of the planting conditions.
To create a soft and relaxed look with annuals and small perennials, plant in drifts or informally shaped groups of three to five plants. Avoid that evenly spaced bedding plant look by introducing accent plants that are taller or have a contrasting texture or color. You may also want to repeat one variety of shrub or larger hosta throughout the planting to add continuity and avoid a mishmashy look, but plant them in a balanced and harmonious pattern with their neighbors rather than a strictly measured repetition. Good luck with your new planting!
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