Growing Bonsai Plants

It is permissible to grow and keep Bonsai plants. 

However, it will be preferable and more meritorious to plant such trees which bear fruit and give shade to people thereby benefitting people and becoming a source of reward for the person who has planted such a tree. 

The following Hadeeth appears in Saheeh Muslim (#1552): 

عن جابر قال قال رسول الله صلى الله عليه وسلم ما من مسلم يغرس غرسا إلا كان ما أكل منه له صدقة وما سرق منه له صدقة وما أكل السبع منه فهو له صدقة وما أكلت الطير فهو له صدقة ولا يرزؤه أحد إلا كان له صدقة

“No Muslim plants a tree except that whatever is eaten from it becomes Sadaqah (i.e. a means of reward) for him, whatever is stolen from it is Sadaqah, whatever wild animals eat from it is Sadaqah, whatever the birds eat from it is Sadaqah and whatever damage anybody causes to it is Sadaqah.”