How short to cut grass if cutting is fortnightly

Hi all, I live in a purpose build block of flats with a communal garden.

We have had a retired couple come once a fortnight to do basic maintenance. They hoover inside and mow the lawn.

I've taken on the beds as they were neglected. However, what do do with the lawn, it's in terrible condition. It's about 60% to 90% weeds and moss. And some places forget it :-(

Obviously mowing a lawn one every two weeks through the warmer season is not ideal. And due to costs we probably can't increase this to weekly. However, I have a non educated hunch that they are cutting the grass way too short for a lawn that's cut fortnightly.

Please, advice needed on how to maintain a lawns health given these circumstances.

Given another few years I think the weeds would win, and the lawn would need to be replaced.

 

Important not to cut more than 1/3rd off the length of the grass. Whatever length it gets to in 14 days they need to based the cut-height on that.

http://www.lawnsmith.co.uk/amateur/lawn-mowing-for-amateurs/good-lawn-mowing-practices