The first sign of bad bok choy is the color of the leaves and stems. Fresh bok choy has a bright green leaf held together by a creamy white stem. When bok choy goes bad, the color turns as well. Dull or light green leaves and yellow stems are signs of bad bok choy. The most common color change when the green goes bad, however, is the spots that appear on the leaves and stems. Much like the brown spots that appear on overripe bananas, the brown spots on bad bok choy only appear once the green goes past its prime.

Good bok choy is crisp and firm in the stalks and leaves. When the leaves become wilted and the stalks rubbery, the bok choy is ready for the trash. In fact, you should throw away any bok choy with stalks that aren't crunchy or plants with leaves that droop when held at the stalk. Limp and chewy bok choy has gone bad.

According to "Perfect Vegetables," good bok choy should taste like spinach or Swiss chard. As the bok choy ages, the flavor becomes more bitter. This green is edible raw, so feel free to taste it before cooking to sample the flavor and see if you are adding bad bok choy to your recipe.

Bok choy must be stored in the refrigerator unwashed. Washing it adds water to the leaves and stalks that can damage them while they sit in the fridge. The dry bok choy can be stored in the refrigerator for up to five days before cooking.