Supermarket Leeks

I've had a fair few years growing leeks, and they've always been brilliant, I love growing them , they're pretty undemanding and creamed leaks with a roast dinner is one of my favourites.  This years haven't been so good though, I tried planting them in a tub instead of the beds as I'd read somewhere they do well, but I think I may have over filled it. 

My question though isn't related to those leaks, but the ones which I had to buy today for tomorrow's dinner...

Leeks that I've grown in the past have been thick, tallish but never straight.  I've also never had more than about 8" of white flesh on them, and then the leaves begin to green up and spread outwards.  The ones I saw in Te*co todayu though were dead straight and had around 12" of white on.  Do supermaqrkets have a special way of growing leeks like this?

Thanks!

I think they may have a sheath or something put on them too.  I use news paper to bleach mine, pehaps the supermarkets just put their shades a bit further up the plant.

I think if every leek in a 20 acre field had a sheath around it the price would be sky high. When they are planted they must plant deeper with whatever machine they use.

Found this, Pf8PLxJ55Lk