Do you need to wash your homemade tie dye shirts in vinegar after dyeing them?

Yes. The vinegar "sets" the color to prevent fading. Use a teaspoon of salt also. However, according to an article at http://www.pburch.net/dyeing/dyelog/B1063361308/C1605100905/E20080723120359/ vinegar is not recommended where the tie dye shirt is cotton.