Adding sugar water to plants typically harms them or stunts their growth. The roots of most plants are not designed to absorb sugar; plants generally make all the sugar they need through photosynthesis.
Sugar water lowers the osmotic potential of water located in the soil, making water less available to plants. This is because water potential in plants must be lower than the water potential in the soil to allow water to flow from the soil into the plant.
In some cases, sugar water can help plants grow, although excessive amounts are harmful. Plants growing hydroponically or in petri dishes need sugar as a carbon source to help them sprout. This is especially true for young plants and tissue plant clones that can't effectively produce sugar through photosynthesis.