Juve - how about we look at this at the cellular level? After all, that's where most definitions of life arise.
Plants and animals are both made of cells. While there are differences between the two, there are lots of similarities and both work by the same general processes eg. respiration of nutrients by mitochondria to release energy, transport of substances, protein synthesis etc etc. Plant and animal cells are unquestionably alive. Therefore, plants are alive as well as animals are. Rocks, however, are not made of cells and do not carry out any of these processes of homeostasis.