Combine boiling water, lemon juice, lavender and rose petals. Let stand for 20 minutes. Strain the solids through a fine mesh sieve, discarding the solids.
In a heavy pot, combine the juice from the previous step with the powdered pectin, stirring well. Bring to a rolling boil over medium-high heat. Add sugar, stirring well, and bring back to a rolling boil. Boil hard for two minutes, stirring constantly. Remove from heat.
Skim foam with a metal spoon.
Ladle hot jelly into hot, sterilized 8-ounce jars, leaving 1/4" headspace. Wipe jar rims. Adjust lids and bands.
Process filled jars in a boiling water canner for five minutes (begin timer when water returns to a boil). Remove from heat and let cool in water for ten minutes.
Remove jars and let cool.