Watering a plant with orange juice can prevent the plant from absorbing the nutrients it needs to grow, stunting its growth or possibly killing it. This is due to the sugar that is found in orange juice. Much like salt, sugar absorbs water.
The effect of watering plants with juice depends greatly on the amount of sugar in the juice. For example, unsweetened apple juice, while still containing sugar, does not contain as much sugar as orange juice. As a result, unsweetened apple juice has less of a negative impact on plants.
The rule of thumb is to avoid using any kind of citrus juice on plants. This includes everything from orange to grapefruit juice. These types of juices have too much acid, which breaks down a plant's immune system over time. A plant with a weak immune system is much more susceptible to fungus, bacteria and mold growth. The sugar that is in the citrus juice also attracts insects, some of which feed on plants.
According to Gardening Know How, there are some benefits to using orange juice on plants in terms of providing the plant with extra nutrition. However, the orange juice has to be used sparingly and heavily diluted. Only about 2 tablespoons of orange juice is recommended for every 1 quart of water.