Starlord answered...."Depending on how well it's growing, first mowing can
be from 2 to 3 weeks........."

This depends on the type of mower used.
If you are using a cylinder mower, where the blade cuts against the sole
plate, you can cut after 3 or 3 weeks, but if you are using a rotary mower
you should leave it longer for a good root system to develop as the grass is
pulled during cutting especially if the blades are at all blunt

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk