hey,
i'm interested to get this project done for you because i did this same project in my fresher year. Anyways it will be an arduino based system which will water plants only when they are thirsty, turns on light depending upon how much sunlight is received and an alarm when the temperature drops.
If you want to know the further technical know hows, feel free to contact me.
optional: Only if you wish to slightly raise your budget, we can easily get this whole system attached to your mobile phone as well. So when any error occurs, it sends you a SMS.
Yes i'm very new to this site but its been my hobby for long. So you rely this project upon me :)
Have a good day!