Overwintering this cold-hardy green is easy!  For successful overwintering, it is important that you thin your spinach to decrease competition between plants and increase air circulation.  Once your spinach has developed 3 sets of leaves, thin seedlings to 4-6” apart.  If you end up pulling out lots of healthy looking seedlings and have more room in your garden, transplant them to increase your fall and early spring harvest!  You can always pull them out when you need to make room for spring crops.