Take a look straight down thru the top of some plants and see if you can see the beginnings of any tassels. They'll be green but won't look like leaves.
Are there any silks? Tassels and silks should arrive at about the same time so that the tassels can drop pollen on the silks. If neither silks nor tassels are present, but you just need to wait a bit longer.

As it turns out, I've been researching this today because I have tassels but no silks (I have popcorn which is about 7ft tall, but others are talking about sweet corn as well). Long story short: it's been an odd year with all the rain. The tassels will come, and don't be surprised if the silks don't come for a few weeks afterwards. Everyone is reporting average or better crops even with the silks coming well after the tassels, so it seems patience is in order...

Cheers,

Tim

Thanks guys.... I pulled the trigger to soon.... i was just down in the garden (micro farm??? how bigg does it have to be to be conscidered a micro farm) and the tassles are starting to show