…but sand and dirt lodge inside the plant as it grows

So maybe don’t use your super expensive usuba/nakiri/guyto to take it apart to clean? You’ll chip the edge. More seriously, sand is my one issue with leeks — and I’d theorize might be why classic French kitchen knives are made with more malleable steel and sharpened to just twenty degrees. The sand bends the edge over, but that’s easily put right with a steel.