Pick or shear the mature cowpeas from the plants once they are plump and firm. Snap off or clip the small stems that hold them to the plants with your fingers or garden shears.
Place the harvested cowpeas into a harvest basket as you pick them. Dump the harvested cowpeas into a colander and rinse them under cold water in a sink.
Split the shells open one at a time with your fingers and thumbs and separate the two halves of the shells to hull them. Pull out the cowpeas from inside the shells and empty them into a separate colander.
Rinse the shelled cowpeas in the colander under cold water in the sink.