Place cucumbers in a large pot and cover with ice cubes. Let sit for at least 2 hours and up to 8 hours. Drain and pat dry.

Place water, vinegar, sugar, pickling salt, and pickling spice into a large saucepan. Bring to a boil; simmer for 15 minutes.

Sterilize the jars and lids in boiling water for at least 5 minutes. Pack cucumbers into the hot, sterilized jars, filling the jars to within 1/2 inch of the top. Place 1 dill head and 1 garlic clove into each jar. Pour hot pickling liquid into the jars, filling to within 1/4 inch of the rim. Wipe the rims of the jars with a moist paper towel to remove any food residue. Top with the lids and screw on the rings.

Place a rack in the bottom of a large stockpot and fill halfway with water. Bring to a boil over high heat, then carefully lower the jars into the pot using a holder. Leave a 2-inch space between the jars. Pour in more boiling water if necessary until the water level is at least 1 inch above the tops of the jars. Bring water to a full boil, cover the pot, and process for 5 minutes.

Remove the jars from the stockpot and place onto a cloth-covered or wood surface, several inches apart, until cool. Once cool, press down on the top of each lid, ensuring the seal is tight (lid should not move up or down at all). If any jars have not been sealed properly, refrigerate them and eat within two weeks.

Store the sealed jars in a cool, dark area. Wait at least 1 week before opening.