I do this all the time and it works well! I find that as long as you dry the lettuce/greens well and put them on the top of the jar, the salads keep and stay fresh for 5 or 6 days. I bought screw-on plastic caps for the Mason jars, which makes it handier. I add meat or tuna separately.
My source for the idea was a different site...I blogged about salad-in-a-jar some time ago--if you want more info. you can find the source on my SparkPage.
Lettuce stays nice and crisp if you put the dressing on the bottom and the "hard" stuff on top of that (nuts, bell peppers, cucumbers, beets, radishes, seeds, apples, etc) followed by the more mushy veggies and fruits (tomatoes, mandarin oranges, mango, etc) and then followed by the lettuce AND if you can put a napkin on top of the lettuce before sealing it up - even better. I love doing things like this cause it makes my week so much easier when I'm on the go :)
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