sweetcorn

they are not leeks LOL

Quite the opposite -  try not to disturb the roots too much as this can make them sulk or even stop growing at a time when you want maximum growth, so carefully plant the rootball and pot contents in the planting hole.  I tend to plant my sweetcorn a bit deeper than the original soil level as this helps to anchor/bed in the plants better (and then they also send out roots near the soil surface)

That advice is here
http://www.allotment-garden.org/vegetable/sweetcorn-growing/