These tender plants grow only in a greenhouse or a hothouse. You can buy a greenhouse at the Shop (click on the icon of the house and you'll find a greenhouse; it's available from level 12; you can buy it for coins). You can use it to grow cotton, pumpkin, sugar cane, tomatoes and watermelons. You can also grow these plants in a hothouse (you can buy it at the Shop for emeralds) that allows you to grow more plants twice as fast! All our shamans grow plants for their potions in the hothouses!