Answer: In my experience hard run off such as this can damage plants primarily due to compacting the soil (terrible for container plants) and sometimes by actually breaking them as well, and the pebble-lined gutter must remain free running or it will not be able to carry the water away quickly as it needs to. If you plant into it the plants' roots will create blockages in the trough and soon leaves and other debris will collect and it will essentially "silt up" to the point it won't function any more. You may want to cover the pebbles with a fine screening much as one might protect a traditional gutter so you can periodically sweep it clean. So instead of planting in it I would suggest you plant in front of it. This will provide visual screening but still allow you access to keep the trough free-running. It will also allow you to select nearly any sun loving plant. One that might be interesting and might begin to grow onto your pebbles is the ornamental strawberry. It is short, tidy looking, semi evergreen and grows quickly to form a solid mat. There are several types of Walsteinia that might do. Your local professional nursery staff and/or county extension may also have suggestions. Best of luck with your project!
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