In a large bowl, combine rhubarb, cherries, white sugar, brown sugar, cinnamon, nutmeg, cardamom, flour, and salt. Mix until evenly blended.
Cut the butter into small pieces and add to the rhubarb mixture. Stir until evenly blended.
Line a 9 inch pie plate with one of the pie crusts. Pour the rhubarb mixture into the crust, and top with the remaining crust. Crimp the edges to seal.
Bake in preheated oven for 30 minutes, or until crust is golden brown.
Interesting Facts
Rhubarb is a vegetable, not a fruit.
Rhubarb is related to the garden sorrel.
Cherries are a good source of Vitamin C and dietary fiber.