when the silk tasssel has withered the sheath can be gebtly pulled back and if the corn looks plump go for it. bearing in mind shops sell the finger sized under developed corn to eat. then any time really.

Normally when the tassels turn dark brown, having said that it is sometimes better to check one first by stripping back a few fronds and squeezing a corn seed.

If it runs milky white then get them eaten,if they are fully formed and the seeds feel quite hard then they may have gone over and won't be quite as tasty.

Sometimes when they are very small and pale coloured and the tassels are brown you might as well treat them as mini corn and eat them!

I hope that helps!

BTW I picked most of mine yesterday!