Cheap and green -- those are two claims made about using plain table sugar as a fertilizer for lawns. The idea is that it's kind to the environment; inexpensive and easy to apply; provides nutrients for beneficial insects, worms and microbes; fortifies grass; and discourages weeds. While having more green in your wallet and on your lawn is attractive, the only scientific study that proves any of the above claims found that sugar kills some plants.
Green plants don't need sugar added to their diets because they are fully capable of making all the sugar they need. All that is required is carbon dioxide, water, light and chlorophyll, and nature does the rest to produce sucrose, fructose and glucose in a process called photosynthesis.
Instead of being a fertilizer, sugar might be an effective herbicide, suggests a three-year research study conducted at Charles Sturt University. In the study, sugar was spread on patches of weeds. Instead of feeding the weeds, it fed micro-organisms in the soil which, in turn, absorbed the nutrients in the soil and starved the plants. Use caution if you decide to try sugar as an herbicide to kill lawn weeds, as applying it to the grass may kill it along with the undesirable weeds. Most herbicides are indiscriminate and will kill desirable plants too.