From next Monday (6 April 2020), Barnet’s fortnightly garden waste collection will become a paid-for service. (You can still sign up for this; you might consider sharing the cost with your neighbours.)
However, Barnet has recently advised that all green waste collections will be suspended for the time being so that it can “prioritise services that help protect and ensure public health”. If you have already paid you will not lose out: your green bins will be emptied for a full year once the service resumes.
More details.