Asparagus can be frozen without blanching it first but if you do freeze the asparagus without blanching the texture nutrient content, flavor and color will be compromised.
Asparagus contains enzymes that break down overtime in the freezer which causes the asparagus to lose the texture, taste, flavor, color and nutrients.
So if you want to make sure the asparagus keeps well and fresh in the freezer you should really blanch the asparagus first before you freeze it.
If you don't blanch the asparagus before freezing it the asparagus can lose it's quality and go bad within a month or two.
But if you do blanch the asparagus first before freezing the asparagus the asparagus will last for up to 12 months frozen.