Separate the petals from the green parts of the flowers.
Pour 1 quart of boiling water over the petals and let steep for 1 hour to make dandelion tea.
Strain the flowers away from the tea, being sure to squeeze out as much liquid as possible.
Add 3 cups of the dandelion tea to a pot, along with the lime juice and zest.
Mix 1/2 cup of sugar to a small bowl and mix in the powdered pectin.
Add the sugar-pectin mixture to the pot.
Bring to a boil and then add the remaining 5 cups of sugar.
Return to a boil and boil hard while stirring for 90 seconds.
Remove from burner, check for "jell" by scooping up a small amount with an ice-cold spoon. Allow to cool just a little and make sure the jelly is setting up. (If not, return to a boil for another 30 seconds or so and try again.)
If the mixture jells to your liking, add in the vanilla extract, mix well, and proceed to filling your jars.
Process jars for 10 minutes in a water bath canner.