Trim woody ends from asparagus and cut to fit chosen jar(s) so the spears can be completely covered in brine.
Add pickling spice and garlic to jar. If using multiple jars, divide the pickling spice evenly, and use 1 clove garlic per jar. Stuff asparagus spears into jar, standing with tips up.
In a small saucepan, combine vinegar, water, and pickling salt. Bring to a boil, whisking to dissolve salt.
Pour hot brine over asparagus, filling the jar with ¼-inch headroom. The asparagus should be completely covered, but you might not use all the brine. Use a chopstick or wooden dowel to remove any air bubbles, then add more brine as needed.
Screw on lid(s) and let cool to room temperature before transferring to the refrigerator.
Notes
If using thick spears, blanch in boiling water for 10 seconds and transfer to an ice bath.
For pantry storage, process jars in a water bath canner for 10 minutes.
Let pickle for at least 48 hours before eating for best flavor.