Divide the 3 1/2 cups of peeled ginger in half.
Chop one half into cubes and shred the other half using a box grater or food processor.
Place the ginger into a large saucepan with 4 cups of water over medium heat.
Bring to a boil, then reduce heat to a simmer and cover the pot.
Simmer the ginger until tender, about 1 hour and 15 minutes, adding more water if needed.
Pour the cooked ginger into a fine-mesh strainer, drain, and retain 1/2 cup of the ginger-flavored water.
Place the cooked ginger in a bowl with the retained liquid and cool for at least 4 hours or overnight in the refrigerator.
When ginger is cooled, place it into a large heavy-bottomed pot.
Stir in 5 cups of white sugar and bring to a boil over medium-high heat.
Boil hard for 1 minute, stirring constantly.
Stir in 1 pouch of liquid pectin, reduce heat to a simmer, and cook for 7 more minutes, skimming foam from the top.
Sterilize the canning jars and lids in boiling water for at least 5 minutes.
Pack the marmalade into the hot sterilized jars, filling them to within 1/4 inch of the top.
Run a knife or thin spatula around the insides of the jars to remove air bubbles.
Wipe the jar rims with a moist paper towel to remove any food residue, then top with lids and screw on rings.
Place a rack in the bottom of a large stockpot and fill halfway with water.
Bring to a boil, then carefully lower the jars into the pot using a holder, leaving a 2-inch space between them.
Add more boiling water if necessary until the water level is at least 1 inch above the jar tops.
Bring the water to a full boil, cover the pot, and process for 15 minutes.
Remove the jars from the stockpot and place them onto a cloth-covered or wood surface several inches apart until cool.
Once cool, press the top of each lid with a finger to ensure a tight seal.
Store the ginger marmalade in a cool, dark area.
