Gather. Pick fresh, fully bloomed dandelion flowers from an area that has not been sprayed.
Prep flowers. Remove as much of the green base as possible by rolling the end of each flower between your fingers to release the yellow petals. This helps prevent bitterness.
Start dandelion tea. Measure 4 cups of yellow petals and transfer them to a heatproof bowl. Bring 4 cups of water to a boil. Pour the boiling water over the petals. Cover and let steep for 12 to 24 hours.
Prep for canning. Wash the jars and place them in the water bath canner. Fill the canner so the jars are fully submerged and bring the water to a simmer. Prepare lids according to the manufacturer’s instructions.
Strain tea. Strain the dandelion tea through cheesecloth or a fine mesh strainer. Measure 3 cups of dandelion tea into a large pot.
Add pectin and lemon juice, briefly boil. Add the powdered pectin and bottled lemon juice. Stir continuously and bring to a rolling boil over high heat. Boil for 1 minute.
Add sugar, boil again. Add the sugar all at once. Bring the mixture back to a full rolling boil that does not stop when stirred. Boil for 1 minute, stirring continuously.
Skim. Remove from heat and skim off any foam.
Fill jars. Ladle the hot jelly into hot jars, leaving 1/4 inch headspace.
Apply bands and lids. Wipe the rims clean with a clean, damp cloth. Apply lids and bands, tightening the bands to fingertip tight.
Process. Place jars in the canner. Make sure the water covers the jars by at least 1 inch. Bring to a full boil and process for 10 minutes, adjusting for altitude as needed. Turn off the heat and let the jars sit in the canner for 5 minutes. Remove jars and let them cool undisturbed for 12 to 24 hours.
Cool. Check seals. Lids should not flex up and down when pressed. Store sealed jars in a cool, dark place for up to 1 year, or according to your manufacturer’s recommendations. Refrigerate after opening and use within 3 weeks.