Spray loose dirt and grime from the retaining wall with a garden hose, starting at the top of the wall and sweeping the hose back and forth as you move downward.
Fill a large spray bottle with white vinegar. Spray the lime deposits on the retaining wall generously with the white vinegar. Leave the vinegar on the wall for 30 minutes.
Scrub the lime-deposit stains with a stiff-bristle brush. Add more vinegar if needed to remove the stains completely.
Rinse the retaining wall with the garden hose, aiming the hose at the top of the wall and slowly moving it back and forth as you make your way down the wall.