Add the rhubarb, strawberries and sugar to a large saucepan and stir.
5 cups diced rhubarb, 3 cups diced strawberries, 2 1/2 cups sugar
Place the pan over medium heat and cook, stirring occasionally, until boiling.
Boil for 15-20 minutes or until the rhubarb is very soft and falling apart.
Remove from the heat; use an immersion blender to make a more smooth jam if desired.
Stir in the strawberry gelatin until sugars are dissolved.
Two 3 ounce boxes strawberry gelatin (ie Jello)
Pour into jars, filling to about 1/2 inch from the top. The jam will expand a bit when it freezes, so you don't want to fill it to the very top.
Let the jam cool completely on the counter, then screw on the lids.
Refrigerate for up to 4 weeks or freeze for up to 1 year.