Wash the asparagus thoroughly and trim the woody ends, cutting the spears so they fit comfortably inside your jars.
Blanch the asparagus in boiling water for about one minute, then transfer it immediately into ice water to preserve its bright green color.
Place garlic cloves, dill sprigs, mustard seeds, and peppercorns into clean glass jars.
Arrange the asparagus spears vertically inside the jars, keeping them tightly packed but not crushed.
Heat vinegar, water, salt, and sugar together until the salt and sugar dissolve into a clear brine.
Pour the warm liquid over the asparagus until every spear is completely covered, then allow the jars to cool.
Refrigerate for at least one day before serving, allowing the garlic and dill flavors to infuse throughout the asparagus.