|What would be a good backdrop for a free standing fountain 5' tall in front of a window|
I assume you mean a plant. There are many great choices but your best bet is to go with an evergreen so it can form a solid wall of foliage year round to bring more attention to the fountain. Some good options include Bright N Tight Carolina Cherry Laurel, Little Gem Magnolia (a dwarf type of southern magnolia), or a vine on a trellis (Confederate Jasmine, Sanbac Jasmine, Pink Jasmine, Cape Honeysuckle, Coral Honeysuckle).
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