"Derek" wrote in message ...

Why a greenhouse? , does very well outside

True I'm a bit lazy and lost some asparagus a few years ago, due to neglect.
With the greenhouse, I'm happy to spend a rainy day, doing a bit of weeding.

would each plant produce new growth this year?

Without doubt, but you should not be harvsting any until the plants
are at least three years old, and then just a few.

Yes, I'll hold fire till 2020.