Unhealthy Plant

• Although kale is a relatively hearty garden plant, it isn't impervious to infection. Yellowed leaves indicate a potential infestation of block rot or a fungus. Aphids or cabbage root maggots are pests that can cause the leaves to wilt and yellow, too. Yellow leaves also indicates that the plant did not grow properly due to a deficiency of nitrogen in the soil or exposure to cold weather.

Go for Green

• Kale comes in several varieties, including ones with bright green, ruffled leaves and those deep blue-green flat leaves. A rich green color is the hallmark of fresh, nutrient-rich kale. You should find it in a chilled section of produce -- kale that gets too warm may wilt and taste bitter. Along with avoiding yellowed leaves, you should also skip specimens with brown or limp leaves.

Old Leaves

• If you've left kale in your fridge for too long, the leaves may wither and yellow slightly. Not only will these yellowed leaves not taste good, they don't deliver the nutrient value of fresh. Once the leaves are picked, their nutrients begin to break down. By the time the kale leaves have yellowed, most of the valuable minerals, vitamins and antioxidants are gone.

Keeping It Fresh

• To keep your kale as fresh as possible, store in a plastic bag in your vegetable crisper, or the coldest part of your refrigerator. Don't wash it as this may cause it to mold or yellow more quickly. Kale should stay fresh for four days and as long as a week, but its flavor may become more intense as it ages.