Prepare boiling water canner. Heat jars in simmering water until ready to use, do not boil. Wash lids in warm soapy water and set aside with bands.

Wash blueberries under cold running water then drain.

Assemble and measure ingredients.

Crush blueberries one layer at a time with a potato masher. Combine blueberries, white grape juice, lemon juice, and pectin into a wide saucepan or jam pot. Stir in pectin until well combined. Bring mixture to a boil over medium heat. Stir the honey into the fruit mixture and return to boil. Cook for about 10 minutes, stirring occasionally.

Turn off heat, skim off foam as necessary, and stir in the dried lavender.

Ladle hot jam into a hot jar leaving ¼-inch headspace. Remove any air bubbles. Wipe jar rim. Center lid on jar and apply band, adjust to fingertip tight. Place jar on the rack in boiling-water canner with simmering water (180°F). Repeat until all jars are filled.

Water must cover jars by 1 inch. Adjust heat to medium-high, cover canner, and bring water to a rolling boil. Process pint jars 15 minutes, adjusting for altitude. Turn off heat and remove cover. Let jars cool 5 minutes. Remove jars from canner; do not retighten bands if loose. Cool 12-24 hours. Check lids for seal, they should not flex when center is pressed.