Greenfield or Green Field

From a CNN story

http://www.cnn.com/2011/TECH/social.media/07/12/google.plus.reboot/index.html?iref=NS1

Much as I've tried to tame my network, it feels more like a hydra or the carnivorous plant from 'Little Shop of Horrors' than the calm and orderly information drag net that I thought I was weaving," wrote Alexis Madrigal, an editor at The Atlantic, in a post titled "Google+: In praise of starting over."

"I needed a greenfield in which to grow a different network."

And from Wikipedia's Greenfield Project entry (no citations, though):

In many disciplines a greenfield is a project that lacks any constraints imposed by prior work. The analogy is to that of construction on greenfield land where there is no need to remodel or demolish an existing structure. Such projects are often coveted by engineers.

In wireless engineering jargon, a greenfield is a project which lacks any constraints imposed by prior networks.

and

A Greenfield Investment is the investment in a manufacturing, office, or other physical company-related structure or group of structures in an area where no previous facilities exist. [1] [2] The name comes from the idea of building a facility literally on a "green" field, such as farmland or a forest. Over time the term has become more metaphoric.

What's wrong with "green field"?