Wash sesssions are harsh on fabrics, more so for natural fabrics than synthetic ones. The more you wash, the faster it wears out. Wash your Zenora sheets in the most gentle machine setting.
Detergents are harsh chemicals designed to be tough on stains. But unfortunately, they are also tough on the fabric. Use gentle detergents, do no use more than the recommended amount. Avoid bleach or fabric softeners. It doesn't get softer than Zenora sheets.
Wash in cold water. Hot water in harsh on natural fabrics. Line dry in shade. Direct sunlight can cause color to fade. If line drying is not an option, then tumble dry on low. Shake out the sheets between washing and drying. If desired, iron at a low temperature.