How to wash a Longaberger basket fabric insert?

definitely hand wash. First soak it overnight in a mixture of liquid laundry detergent, baking soda and warm water. In the morning, gently wring out the fabric, rinse, and wring again. Roll it up in a towel before the final wringout. Then, if you have one of the plastic inserts, put it over that (upside down) while drying. If not, shape it as best as you can as it dries, to lessen the need for ironing.

those baskets are collector items and fetch a good price in antique shops. I would personally have them dry cleaned. Then you'll be guaranteed results with no shrinkage

I had success soaking mine in oxyclean and washing them by hand, and then air drying them.

I wash them in the machine, but place them in a starch bath, then lay flay to dry.

Here is an article that might be helpful - http://www.ehow.com/how_4856832_clean-longaberger-baskets.html - good luck