Asparagus are a low acid vegetable with a pH of 6.00 to 6.70, so they must be pickled to safely water bath process.

nchfp.uga.edu/how/can_06/pickled_asparagus.html

Otherwise, they must be pressure canned. nchfp.uga.edu/how/can_04/asparagus_spears.html

You can dry asparagus, though only the top 3 inches are recommended. Blanch them for 5 minutes first, and then dry in a dehydrator at 135°F until brittle, 6 to 10 hours.

To freeze, blanch cut or whole asparagus for 4 minutes (thin spears for 2), chill in the fridge, then freeze in freezer baggies. They hold for 8 to 12 months before the flavor starts to degenerate.