How to store spinach to extend its shelf life?
Fresh spinach, like other leafy greens, is best stored in the fridge in some way that keeps it dry but not too dry.  The things that cause spinach to wilt and spoil are:


dirt &amp; insects
being wet or too damp
getting too dry
cut, crumpled, and broken leaves


I've included a number of references below, but here's my method that allows me to store fresh spinach for up to two weeks:


If the spinach is sandy or dirty, separate bunches, wash in several changes of cold water and spin dry them.  This is even more important if the spinach has any insects.  Cut off any dirty roots, but do not trim off stems.
Having made sure the spinach is thoroughly dry, wrap loose bundles of it in a couple of paper towels, and then put these bundles in plastic bags.  Do not overpack the bags.
Store the plastic bags of spinach in the fridge, preferably in one of its more damp spots like a vegetable drawer.  More importantly, do not stack anything on top or jam the spinach in a tight space.


This way, fresh spinach can keep for up to two weeks in the fridge.  If you need longer than that, then chop, blanche, drain, and freeze it.

Resources:


https://www.thekitchn.com/we-tried-3-ways-to-store-salad-greens-and-heres-our-winner-tips-from-the-kitchn-211770
https://dawnjacksonblatner.com/2018/03/make-your-leafy-greens-last-longer/
http://pickyourown.org/freezing_greens.htm