There are a few different ways i have stored greens in the past. How long they last really depends on how fresh they are when bought. Lately I have been having a hard time finding greens that are not already wilted or rotting at the store, which is really annoying. It seems now that i am further south, the green quality is crappier compared to when I lived up north. These are also greens I don't expect to be grown locally either.
Anyway, with fresh greens they can keep good for up to two weeks with either method mentioned below. However the older greens get their nutrient value starts to deteriorate. Maybe 10-15% can't remember the exact percentage.
Freezing greens tends to result in a mush. Leafy greens are just too delicate to take the freezing process. Denser greens are ok, like cabbage, collards, kale. Vegetables such as carrots, peas, beans etc are fine frozen too. However some nutrients are damaged when frozen..thaliamin being the main one so dusting with a multivitamin is good if you use alot of frozen greens.
I typically either store in the bags the greens come in, if they are not soaking wet (stupid store misters). If wet, they rot very fast. These I dry off first, at least shake dry.
Another method I have used is I layer the greens between paper towel after washing them. Doing this way tends to last the longest, but the work to do it with three or four different leafy greens, is a pain. Now I just don't bother.
A third method which almost guarantees you don't' have any wasted greens, is to buy more vegetarian or omnivorous animals LOL. Or start eating really healthy salads
Everything you feed your bearded dragon is totally safe to eat yourself, including the bugs but I Certainly understand if you rather substitute the bugs with chicken, pork, beef or fish.
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PHLdyPayne