If you want a perpetual supply of kangkung

This was my harvest from one box today...

If you wanted that quantity every 2 or 3 days, all you need are 4 boxes like this...

You can see the leftmost box which has just been harvested. Notice some yellow leaves on the bottom from the shoots that did not get enough light. 

I harvest from right to left every couple of days. The rightmost box is ready and will be cut in a day or 2.

This method has been serving us for months now. No idea if they will stop producing since many have sprouted flowers. I will let you know if they slow down to a pace that cant meet our demand.