This is what my fresh organic baby spinach looked like:
And the green leaf lettuce:
I washed, spun, and sorted the greens and put them in pint canning jars and vacuum sealed them. This worked very well with the romaine lettuce, though technically romaine lettuce keeps pretty well in the refrigerator even without vacuum sealing. The same cannot be said for green leaf lettuce, however.
After one week, the spinach was basically indistinguishable from the original. I still have a jar in the refrigerator so I'll check back after two weeks.
Same is true for the green leaf lettuce, which is even more impressive because it had been torn into pieces a week prior and were ready to just drop on a plate and make a salad:
I like this preparation because not only do the greens keep much better, but they're already washed, sorted, and prepped; I can immediately put them on a plate for salad. With spinach, I often toss it in a sauté pan and wilt it, then add a little hana katsuo (Japanese dried bonito fish flakes) and soy sauce as a vegetable side:
And 13 days later, my spinach still looked pretty good, too:
Update 6/20/2012: I've made a new vacuum sealed salad post with my latest best practices, but this post and great salad experiment are still a good read.