Title: Because My Land Is Fair
Source: LoTR (Fourth Age)
Disclaimer: Middle-earth belongs to Tolkien and his heirs: I wander there for fun, not profit
Because My Land Is Fair
Legolas crouches to scrape up a handful of soil, rubs it between his fingers, sniffs it; cautiously touches a fingertip to his tongue. Then he sits back on his haunches and smiles, satisfied.
“It's almost clean here, Taurlaegel. Treebeard was right – the mustardseed, the pigweed, the alpine pennycress have done their work as he said they would, leaching the metals and the slag and the poison of the Orcs' mining from the soil. The streams are running clear. Another sunround or two, and we'll be able to start replanting the trees. Ithilien will be restored.”
It's purely my speculation, but having seen some of the damage and wanton vandalism to land and trees wrought by the Orcs in parts of Ithilien (around the Crossroads, for example), and knowing what a foul and noisome state their mining for metals and other activities had left the land in closer to Mordor, I have a theory that part of Legolas' reason for bringing some of the Mirkwood Elves south to Ithilien may be to work to undo some of what the Orcs had wrought. The use of plants such as mustardseed and pigweed for what is, I discovered, called "phytoextraction" (leaching heavy metals from contaminated soil) is genuine: see the Wikipedia entry for details (isn't it amazing how educational writing fanfic can be?)