Fresh cucumbers are a tasty addition to a garden salad and sandwich. Sliced or whole cucumbers also make for delicious homemade pickles. Using the cucumber when it is ripe ensures you get the full, desirable flavor out of vegetable. Doing so also prevents you from accidentally ingesting a rotten item that bothers your stomach. The ripeness of a cucumber is determined by a variety of factors, including how the item looks, feels and smells.
Squeeze the cucumber gently. A ripe cucumber is firm, with little to no give. Choose a different cucumber if the one you're gripping seems soft.
View the color of the cucumber. A ripe cucumber is medium to dark green in color. Discard the cucumber if you notice any yellow areas or dark spots on its outside surface.
Look at the tips and ends of the cucumber. Cracks or indentations are signs that the cucumber isn't right. A ripe cucumber, according to the Sustainable Enterprises website, also has a "moderate, uniform diameter" similar to that of a sausage.
Smell the outside of the cucumber. Discard it if you notice any foul odors, as a ripe, usable cucumber has no such smell.