Vegetables have many different vitamins, minerals and phytochemicals in different quantities. Eating a variety is important in order to get all of the nutrients in sufficient amounts. If you are eating and juicing vegetables, then by all means juicing a single vegetable would be fine (always change it up). If your only intake of vegetables is via juice, then using a mix of vegetables would be important. However, keep in mind that vegetables are a great source of fiber. Adding pulp back into your juice can be beneficial. Eating the whole vegetable will provide the most nutrition benefits and fiber. For the best nutrition, aim to make half-your-plate fruits and vegetables at every meal using all different forms of produce (dried, 100% juice, raw, canned, and frozen).