Generally speaking, woven cotton should shrink only with the first wash & dry. (Some cottons will even shrink in width, no thanks to some unscrupulous manufacturers)

If subsequent wash & dry are at higher temps than the previous wash & dry events, it is entirely possible the cotton will shrink.

Woven cotton normally will not shrink after that, unless the first wash was cold and subsequent was hot, etc. etc. When sewing with flannel, however, the rule of thumb is (hot) wash & dry x 3.

As always, YMMV.

Thanks so much. I will dry them outside then.