Prepare a pressure canner by beginning to bring it up to temp. On the side, start a pot of boiling water for filling the canning jars.
Trim asparagus to fit into the canning jars (anything smaller than a quart, wide mouth recommended).
For raw pack, pack asparagus into jars raw, trimmed to size. For hot pack, blanch asparagus in boiling water for 3 minutes then pack.
Add salt if desired. The recommended amounts are 1 tsp per quart or 1/2 tsp per pint, but I personally prefer less. Salt is optional.
Pour boiling water over the asparagus in canning jars, leaving 1'' headspace.
Process in a pressure canner at 10 pounds pressure for 30 minutes (pints) or 40 minutes (quarts). For other jar sizes, round up (ie. 12 oz jelly jars use pint times, and 24 ounce pint-and-a-half jars use quart times). Be sure to adjust pressure to altitude above 1000 feet (see note).
Allow the pressure canner to cool completely before removing jars.
Notes
Above 1000 feet in elevation, you must adjust pressure to altitude. If you're using a weighted gauge pressure canner, that means using the 15 pound setting for any place above 1000 feet.