I plant my leeks out as plants (pencil thick) in rows only 8″ apart,4″ between leeks ,in jUNE/july.I often use them to replace broadies.
Sweet Corn would be planted out mid May, normally as a block or square, 12″(300mm) each way, so as not to cast a shadow onto a lower crop. If you want a succession of corn, grow a few of differing varieties. They may cross pollinate, pollination is best when the crop is a block, success whichever way the wind blows!
