Rhubarb was added to the herb garden last year and according to the label you should not pick the first year.
It has gotten quite large in the full sun and neglected conditions here so I have removed a few stalks but left the majority to grow on.

When should you pick your rhubarb?
About the first week of May you should check the stalks. You can start picking when stalks are 12 to 18inches long from late May through late June or early July. Extremely thick stalks are usually stringy and tough so pick thinner ones. Colour will range from green to dark red.
To remove stalk twist at soil level while tugging gently. If they do not pull away from base easily they are not ripe.
You should pick the largest, and only one third of the stalks. More will grow to replace them extending your harvest.

When flowers begin to appear remove top of spikes. Once they go to seed the stalks will be bitter. Harvesting is done for another year.

High Temperature:
Actual: 14°C sun and cloud Wind WNW30km/h P.O.P.10%
Average: 25°C
Record: 33°C in 1945

Low Temperature:
Actual: 7°C mainly clear Wind WNW24km/h P.O.P.38%
Average: 13°C
Record: 5°C in 1988