On Monday this week I visited Wisley and found seeds for this in the shop. Regular readers may remember me mentioning a trial bed that I saw at Wisley a year or so ago (just looked...it was actually March 29th 2007...doesn't time fly!!!).
I was delighted to find the seeds (£4.99 for 200g, sufficient to cover 100sq.metres), with an informative leaflet. I have copied the leaflet here for you....both photos will enlarge for easier reading if you click on them.
I need to study this a while to see how to fit it into my rotation plans. It might be difficult with the new Gertrude Franck method I will be following this year so it may have to wait until next winter. The Gertrude Franck method does actually have some rows sown with mustard if they are for later crops....that may be where it fits in...I'll see.