Mustard greens — Food safety facts
Safe to share · Dogs · full breakdown on the linked food page
Steamed and plain, small amounts.
The full verdict, portion guidance and serving notes are collected on the Mustard greens food facts page.
Short answer
No, one raw leaf is not an emergency. Mustard greens are not toxic to dogs, so a single small bite is very unlikely to cause harm. The main risk with raw greens is that they can be a bit tough on digestion, possibly leading to mild gas or an upset stomach. Just keep an eye on your dog over the next day for any signs of vomiting, diarrhea, or loss of appetite, though these are uncommon from such a tiny amount. For future treats, steaming the greens makes them easier to digest. If your dog seems perfectly normal, there's no need to call the vet.