This actually does less than my proposal because my proposal stops them completely from moving on until they kill the zombie.  Take, for example, if a zombie starts on a square with a weed.  With my proposal, they would be forced to stay on that square, whereas with this they have the opportunity to move off of the square.

If I understand this correctly, it stops the zombie from entering the square with Corn and Weed in the first place, but does not prevent them from leaving if they start in the square.
Your proposal on the other hand, yoda, does _not_ stop them from entering but prevents them from leaving. So, both do stop the zombies but this one stops them one earlier. Which I like, at least as a special feature of Corn and Weed.

What is the benefit of stopping the zombies one square earlier?

Trivial.

[Yoda, mideg, aguy]
No, “Zombie Movement” does not prevent them to leave, it just slows them down: the shambling zombie is free to move the next shamble.

[Ely]
True enough. Even more so is this proposal relevant.

That’s why I put this clause in there: “or if the Zombie is on a Square that contains a Crop or Shed when it starts Shambling”.  That prevents them from moving if they start on a square with a crop or shed.

My bad, I didn’t see it, my eyes hopped that line I guess. One more reason to vote “Zombie movement” down. :)
I’d prefer it not to be a general property, but only a power of few crops. Oh well.

Wow, I checked “Zombie movement” after Elys claim and agreed with him. Oh well, I feel a little stressed atm.