Prep the petals — Trim the white bitter heel from the base of each petal. Rinse gently under cold water and pat dry.
Make the rose infusion — Heat water to just below boiling. Remove from heat, add petals and lemon juice, cover, and steep for 20–30 minutes. Strain through cheesecloth into a bowl — do not squeeze the cloth. Discard the petals.
Add pectin — Pour the strained rose liquid into a clean saucepan. Stir in the pectin. Bring to a full rolling boil over medium-high heat, stirring constantly.
Add sugar — Add all the sugar at once. Return to a full rolling boil and boil hard for exactly 1 minute, stirring continuously. Skim off any foam.
Test the set — Drop a small spoonful onto a frozen plate. After 30 seconds, push it with your finger — if it wrinkles, it is ready. If it runs, boil for 1 more minute and test again.
Fill the jars — Ladle hot jelly into sterilized jars, leaving ¼ inch headspace. Wipe rims clean and seal with lids.
Water bath — Process jars in a boiling water bath for 10 minutes. Remove and leave undisturbed for 12–24 hours until lids pop and seal.