Grit, dirt and bugs love to cling to the undersides of those nutritious leaves, especially with low-growing chickweed. Over the years, I have come up with a method for washing that seems pretty effective. Harvest greens into a large tub or bucket. Fill with water so that greens are submerged, gently stir with your hand and allow to soak for two to five minutes. Scoop handfuls of greens out of the water into a salad spinner, remove spinner basket from bowl and rinse greens under fresh cool water. Spin in salad spinner to remove as much water as possible. Taste a leaf or two to make sure the grit is gone. Repeat the process if necessary.
Submerging then rinsing seems to be effective for the grittiest greens. If yours seem pretty clean after submerging in water, skip the rinsing step. Capture that wash water and put it back in your garden.