http://simplegoodandtasty.com/2010/05/25/tunnel-farming

They are related to carrots, but are the closest relative to parsley.  They are a root vegetable that grow larger the farther north you go.  The early popularity of parsnips was replaced with the potato.  They are planted in early spring, as soon as the ground can be worked. Harvesting can begin in the fall and continue until the ground freezes.  The remaining parsnips can be left in the ground and harvested in the spring.  That process converts the starches in parsnips to sugars making spring-dug parsnips sweeter then the fall-dug ones.  However, spring-dug ones must be harvested before the tops to go seed. 

What do you do with them?  That’s the next question we get after the “what are they” question.

Parsnips can be boiled, roasted or used in stews, soups and casseroles. Roasted parsnip is considered an essential part of Christmas dinner in some parts of the English-speaking world and frequently features in the traditional Sunday Roast. It’s also often paired with lamb for an Easter dinner in some cultures.  Parsnips can also be fried, or can be eaten raw, although raw parsnips are not frequently consumed.

The parsnip is richer in vitamins and minerals than its close relative, the carrot. It is particularly rich in potassium and a good source of dietary fiber.

For more information on parsnips check out:  http://www.answers.com/topic/parsnip