We've grown sweetcorn for the last four or five years, ususally about 24 plants or so. We start them in the greenhouse - this year I've used the insides of toilet rolls. The plats are now about 6" high and will be going out this weekend, all things being equal. We've had mixed results depending, I think, on the weather. Last year we had a good number of cobs but they didn't ripen well - but the chooks loved them and they are very convenient to hang up for them!