I am trying an experiment right now for this. I believe I know what you are referring to...a natural lawn rennovation site What the sugar does is increase the microbes in the soil. The sugar is sort of like a fast food for the microbes. A study was done in Pierce County on the Prairie where sugar was spread in areas where there were invasives. This allowed the
native plants to come back and they found that the the native plants were able to come in faster. What happens is this, the microbes increase then do not have enough food there is die off. The die off uses nitrogen in the soil, this allows the native plants to come in more easily. This is what the study suggested.
With weeds A soil scientist explained it to me this way: If you increase the microbes in the soil this creates a healthy enivornment which allows better root penetration. Weeds are opportunists. They will come where soil is poor and deficient and compacted. Lawn is a high feeder. It needs food, nitrogen, protein etc...you need to feed your grass which by default means feeding the soil to get strong roots to compete with the weeds. I have done natural lawn rennovation in Seattle using corn gluten and grass mulching. I am experimenting on a very weedy lawn here in Pierce County using the sugar first, grass mulching and corn gluten. I am hand pulling the biggest weeds. I am trying to mow the lawn to keep the existing weeds down so they do not go to
seed but at the same time feeding what lawn is there to see if it will over time out compete the weeds. My soil in Seattle took three years to become adequate enough to support a weed free lawn. (using no chemicals and not much work) This is a process that takes time. My soil was full of microbes and worms and good things...it was alive and my grass was green and thick and weed free, and needed far less
water. As Paul Stated about the molasses, you are feeding the microbes but there are research citations out there that show that sugar seems to work faster. LOL. I am okay with using sugar although geez will we find out it caused some imbalance? Little microbes with cavities! I think it is better than other stuff. It seems to feed the soil unlike chemical fertilizers. You do have to use the sugar and provide additional food either
compost swept into the grass, (I use corn gluten) or grass mulching.