Hardy means tough––if you're hardy, you don't get tired easily and can endure hardship. People who don't catch cold often attribute this fact to their coming from hardy farming stock.
Before 1200, hardy indicated boldness and daring in battle and was probably influenced by hard. Warriors are hardy: they’re brave and strong and don’t easily tire. Plants and animals can also be hardy if they can survive harsh weather or poor growing conditions. When planting a lawn, you should pick hardy species of grass, which will survive droughts and come back after long, cold winters.