Line slow cooker bowl with baking paper and lay asparagus on paper
Add butter, garlic and S&P
Cook on low for 2hrs (or until soft as slow cooker's can vary in times) Mine was cooked in my 3L and my larger slow cookers would do it much faster so just adjust to your own/to tender
*Alternative*
Rather than cook them on their own you can add the same ingredients to a foil parcel (tightly sealed) and include them in with whatever else you are cooking in your slow cooker over that time frame as per Basic Vegetables method.