2. Vegetables that mature in summer include cowpea, loofah, eggplant, bitter gourd, tomato and wax gourd. Summer is the hottest season in a year, and it is also the most vigorous season for plants to grow, because there is plenty of sunshine and rain in summer. Bitter vegetables are the best vegetables in summer, because they contain amino acids, bitterness and sweetness. It has the effects of clearing away heat, relieving summer heat, resisting bacteria and diminishing inflammation.