For the rhubarb-apple jam, peel the apple and rhubarb and cut into pieces. Place fruit in a large pot with the sugar and citric acid. Let steep cold juice for about 1 hour.
Boil for 15 minutes and then make the jelly test.Before filling, puree the jam and fill into clean jars. Close the jars tightly with the rhubarb-apple jam and put on the lid.