Jennifer Sutcliffe told local station KIII-TV that her husband was working in the garden when he saw the four-foot (1.25m) rattlesnake and decapitated it.
When he picked up the snake's remains to dispose of them, the head bit him.
A snake's bite reflex can be triggered up to several hours after it has died. Ms Sutcliffe told KIII-TV her husband immediately began to have seizures.
He was airlifted from his home near Corpus Christi to hospital where he was treated with the anti-venom CroFab.
More than a week after the incident, the man is reportedly in stable condition, with some weakened kidney function.
Leslie Boyer, an anti-venom doctor at the University of Arizona VIPER Institute, warned against attempting to kill snakes, particularly by cutting them.
"It's cruel to the animal and it leaves you with a smaller piece that's venomous to pick up," she told the Gizmodo news site.