Bring the water to a boil and pour over the peony petals. Allow the petals to infuse for about 10 minutes (or longer if you choose). Strain and discard the petals.
Place the peony petal tea in a saucepan along with the lemon juice and bring the mixture to a boil.
Add the pectin, stirring to incorporate, and return the mixture to a boil for 1 minute.
Add the sugar, stirring to incorporate, and return the mixture to a boil for 1 minute.
Ladle the peony jelly into prepared jars leaving 1/4 inch headspace.
If canning (optional), process in a water bath canner for 10 minutes.
Notes
Canning is optional but makes a shelf-stable jelly. If making a refrigerator jelly, allow the jars to cool completely before storing them in the refrigerator. Without canning, peony jelly will keep in the refrigerator for 3-4 weeks. If canned, it'll store on the pantry shelf for 12-18 months (refrigerate after opening).