Trim the lettuce to fit in your designated jar. I use a gallon glass jar.
If you are using Romaine lettuce hearts, slice the bottoms off so that they will stand flat. If you are using iceberg lettuce, slice it in half and then cut it in 3/4" wide ribbons.
Prepare your designated jar: place the pickling spice in the bottom of the jar. Then the garlic cloves. Then top with your lettuce. I usually stand all 3 romaine hearts upright in my glass jar.
In a small saucepan, combine the water, vinegar, sugar, salt and red pepper flakes. Heat on low until sugar and salt are dissolved. Push off the burner and allow to cool.
Once cooled, pour the brine over the lettuce in your jar. If more brine is needed, double the water, vinegar, sugar, salt, and red pepper flakes as needed. Cover with your lid. Chill until ready to use.
Lettuce will keep in the refrigerator up to 14 days.