This homemade pickled spicy asparagus recipe infuses fresh asparagus spears with spicy flavor from crushed red pepper, garlic, and mustard seed.
Place trimmed asparagus in a quart-sized canning jar. Add garlic, pepper flakes, mustard seed, and peppercorns.
Combine vinegar, water, salt, and sugar in a medium saucepan over medium heat; bring to a boil. Reduce heat and simmer for 5 minutes. Turn heat off.
Pour vinegar mixture over the asparagus. Screw on the lid and let sit until lid has sealed, about 1 hour.
Place in the refrigerator until pickled, at least 2 days.