[angelavdavis]

Only realised yesterday it likes full sun 

This was what I was going to say!  I had two rhubarb plants planted under trees in my garden at home, but they did little.  After one died over winter, I dug up the other one and moved it into sunshine and now it is flourishing.

[Yorkie]

The ones under trees were likely to be suffering from the competition for nutrients and water, rather than shade specifically.

My neighbour has plants which get very little sun and they do fine. 

[Beetroot queen]

Mine only get morning sun till 1 or so and they are fine

[Sparkyrog]

mine are producing fine but the stems are all green ! will move in the autumn 

[Yorkie]

mine are producing fine but the stems are all green ! will move in the autumn 

Are you sure it's a red-stemmed variety?

[Sparkyrog]

I believe its pink champagne