50-60 days. Watermelon radish makes a gourmet conversation piece. This improved hybrid variety has a beautiful rosy-red interior filled with sweet flavor and a tender, yet crisp texture. Radishes average 3” in diameter (tennis ball size) but can grow larger and weigh up to 1 pound each. A winter radish, it grows best when sown in late summer for a fall crop and can be harvested up until the ground freezes. Eat fresh, add to stir-fried dishes and soups, or pickle.