Rhubarb -- when to pick?

So today would be the last day for harvesting anyway then, and there's definitely nothing to harvest as the stems are really quite thin. I can let it just get on and die back and then cover it for the frosts like we did when they were just crowns.
Now I have to wait a year for rhubarb    I love rhubarb crumble!
Does it start growing early next year? What month can you typically start harvesting it?

Once the stalks start getting thin, it's time to stop picking - usuall in a few weeks time.

Once midsummer's past you get more oxalic acid in the stems which can upset some people's tums or bladders 

Rhubarb is essential on my plot.