Molasses is thick syrup by product from the processing of the sugarcane or sugar beet into sugar.
Molasses can be used throughout the whole flowering stage. Some grower prefer to only use molasses during the last 3 weeks.
The ratio per gallon is 1-2 tablespoons, but can be changed due to certain conditions.
Molasses can be used for soil and hydro.
In an experiment Jorge Cervantes had done "the buds swell about 20% when sugar is added to irrigation water during the last four weeks of flowering".
Over-applying molasses will not make buds swell any more, and if over-applied could bring insects to your garden.
A 32 oz bottle of Molasses is about $7.