Touch the skin of the zucchini. If it feels tender to the touch and pricks easily with your thumbnail, it is ripe and ready to eat. Zucchini skin hardens when it is too large or overripe.
Pick the zucchini when it is approximately 6 to 8 inches long or medium-sized. Take care not to remove the zucchini from the vine roughly, as new roots often grow from the joints on the vine. Harvesting smaller zucchini is acceptable if you're using them for eye appeal, steaming them whole or adding to a dish with baby fruit.
Remove zucchini from the vines late in the morning after the dew dries or early afternoon. Disease may spread when plucking them from a wet vine, according to the University of Minnesota Extension.