Place the rhubarb in a large pot over medium heat. Add enough water to cover the bottom of the pan so the rhubarb doesn't burn.
Cook for 5-7 minutes, or until the rhubarb is very soft. Remove from heat and pour into a measuring cup.
Remove stems from strawberries, wash and slice into half.
Mash fruit with a potato masher for best results. If you use a food processor, pulse to chop. DO NOT PUREE. The jam should have large bits of fruit, if desired.
Side Note: (I had exactly 1¼ cups of rhubarb which means I used 2¾ cups of mashed strawberries because you must use exactly 4 cups of mashed fruit for this recipe). Side Note: Reducing sugar, water, pectin or strawberries will result in set failures. USE EXACT AMOUNTS.
Add exactly 3 cups of sugar, 1 cup of water, and one packet of pectin to a saucepan.
Bring mixture to a boil on medium-high heat, stirring constantly. Boil and stir for 1 minute. Remove from heat.
Quickly stir crushed rhubarb and strawberries (totaling 4 cups exactly) into the hot sugar mixture.
Stir for a minute.
Pour into clean containers, leaving 1/2 inch space at the top for expansion during freezing; Cover with tight sealing lids.
Let stand at room temperature for 24 hours until set. Refrigerate for up to 3 weeks. Otherwise, store in the freezer for up to 1 year.