Close to the downtown campus or Loyola
Please refer to Concordia: A Food Guide to Student Sovereignty for more Locations
Montreal has community gardens in 17 of its districts. The yearly cost varies from 10$ to 30$ and you need a proof of residency, but otherwise this is a very cost efficient of growing your own vegetables.
Agriculture Montreal is a website dedicated to urban agriculture. It contains, amongst other things, a guide to start your own rooftop garden and a map of all the rooftop garden already existing in which you can help.