At home, children often have pets that they take care of and play with; even in the classroom it is not uncommon to find a wormery, an aquarium or an ant farm. However, children rarely have the opportunity to own and care for a plant over a lengthy period of time, let alone a tree. The authors describe a project in Portugal aimed at improving children's plant knowledge by giving them the opportunity to own and care for a "pet tree." They chose the cork oak ("Quercus suber" L.) species to work with because it is a common native tree in the area, and one of economic importance. They hoped that experimental activities involving a very common tree, in a constructivist environment, would increase children's interest in plant science; they also wanted to promote learning of several key concepts related to the influence of environmental factors on how plants grow, which are part of the national curriculum for primary grade 5 (age 8-10 years). The authors found that experimental activities involving an important native tree increased the children's interest in plant science, and convinced them that having a "pet tree" is an effective way of motivating children to observe, take care of and love plants. (Contains 4 figures and 1 table.)