I haven't harvested any of my spinach, mainly because I didn't know if it was ready and I didn't really know the best way to do it. I found some helpful information online tonight:
Spinach can be harvested in the cut and come again method of harvesting lettuce. Cut individual leaves, starting with the older, outer leaves, and letting the young inner leaves remain and continue growing for a later harvest. You can also cut down the whole plant, for a larger harvest. If you cut about an inch above the crown or base of the plant, it is very likely the plant will send out a new flush of leaves.
Spinach is a leafy green vegetable that grows best in cool weather. Usually thought of as being packed with iron, spinach is even higher in vitamins A and C, thiamin, potassium and folic acid (one of the B complex vitamins). Spinach, like most dark green leafy vegetables, also contains the carotenoids lutein and zeaxanthin. Oh, and it tastes great eaten fresh or cooked.
All spinach is grown for its dark green leaves. While there are many different spinach varieties with an assortment of leaf shapes and textures, spinach is usually divided into 2 major categories: Smooth Leaf and Savoy, with darker, thicker, crinkled leaves. Since they’ve been crossbred so much, it’s often hard to categorize them. Small leafed spinach or baby spinach has gained in popularity recently. These are not necessarily immature spinach leaves, but varieties that simply don’t get large.