This is a weird bug that we're trying to fix; in the mean time, sorry for the inconvenience!
If you're using Internet Explorer 10 or 11 on Windows 8 or 8.1 and have the zoom level set to anything other than 100%, you will be unable to edit a Plant Card. This occurs if the zoom is greater or less than 100%. We've observed this behavior in both Metro and Desktop mode.
To set the Zoom level back to 100%, there are two options:
1) View Menu (Alt-V) ➔ Zoom ➔ 100%
2) Hit Ctrl-0 (Control + Zero)
The problem does NOT occur on Windows 7 or Windows 10.