Gather the ingredients.
Soak 4 cups dandelion petals in cold water for five minutes to allow time for any insects to exit, then drain.
Place petals in a heavy saucepan along with 4 cups water, 3 lemon slices cut into ¼-inch slices, and ½ vanilla bean split in half.
Bring to a boil over high heat, then reduce heat, and simmer for 30 minutes.
Remove pan from heat and let steep for 6 hours.
Strain dandelion tea through a cheesecloth and discard solids.
Place dandelion tea in a heavy saucepan and bring to a low boil.
Gradually add 2 ½ cups sugar to boiling liquid while stirring until sugar is dissolved.
Lower heat and let simmer uncovered until it reaches desired syrupy thickness. This may take about 1 hour. It will thicken more as it cools.
