aspidistra advice

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I have four huge aspidistra plants, which live on a north facing dwarf wall just at the front of my house. They grow like weeds, but are not as attractive as I'd like because the leaves go pale as they age - not yellow, they are not dying, just not the glossy green that they should be. I'm in the process of repotting and splitting to make smaller, nicer plants - I don#t really have room to keep them indoors, any advice on how to keep the leaves dark please? 

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