There are over 1300 plants that lower blood sugars. Juicing, however, is almost always more effective for lowering blood sugars than herbal medicine. A few herbs, however, can help you stick to your juicing goals.
Cinnamon can lower blood sugar levels slightly. Different kinds of cinnamon have different effects, but the kind of cinnamon used in the English-speaking world is only useful when it's been heated in hot water. Don't bother with dropping cinnamon sticks into hot water and added the liquid to juice. The juicing diet itself makes a much greater difference in your blood sugar control.
Coptis, barberry, and Oregon grape root all contain berberine, a “detoxifier” used in Ayurveda and Traditional Chinese Medicine to prevent the release of glucose from glycogen in the liver. They also are extremely bitter, and you would not want to add them to juice.
Gurmar, which is also known by its botanical name Gymnema sylvestre, is famed as the “slayer of sugar.” If you are having trouble sticking to your juicing plan because you crave sweets, it can reduce your desire for sugar.
Green tea is used in dozens of over “fat burning” products. It is the combination of more green antioxidants than you can get in 40 cups of green tea with no more than the amount of caffeine you can get in about 4 cups of green tea that activates your fat burning metabolism. Don't add green tea to juices unless you like the taste. Take a green tea supplement that contains caffeine instead. Drinking more than 2 cups of coffee per day cancels the fat burning effect of the supplement by supplying too much caffeine. Diet Coke and similar caffeinated sugar-free beverages also can be a problem.
Hibiscus adds an interesting flavor and a deep red color to juices and teas. It slightly lowers blood sugar levels and also helps stimulate bowel movement. Use in moderation.
Koval (the Ayurvedic herb also known as Coccinia cordifolia or ivy gourd) can lower blood sugar levels by reducing insulin resistance. In women it also (1) increases sexual arousal but (2) decreases sexual satisfaction, so most women may want to avoid it.
We don't usually think of coffee as an herb, but it acts in the same way as herbs. Decaffeinated coffee may lower insulin resistance and complement a juicing diet for diabetes. Coffee that has caffeine may cause blood sugar disturbances. Sugar and cream, of course, cancel out the healthy benefits of juicing.