I asked Kevin Matthew Murphy of WSU extension about growing quinoa. Here's what he said:
I would avoid planing into lambsquarters if possible, unless you are fully committed to diligent and timely weeding. We've had good luck with our April 1 west side plantings, so I'd shoot for around then. Either seeding or transplanting works; if transplanting however, be sure to not let the quinoa get root bound.
So it appears that planting at the farm with its clay soil may be iffy. However, some things have grown so well there I expect to give it a try if the soil becomes dry enough soon enough.