Mowing grass at or near the optimal mowing height will keep grass healthy and dense. Higher density means more soil surface shading, which severely restricts the germination of many annual grassy and broadleaf weeds. Maintaining a dense and healthy turf is the best weed control.
Seasons, weather, and nutrient availability, are some of the many things that can affect grass growth. The best and most safe rule of thumb is to never remove more than 1/3 of the leaf blade at any one time. Lawns are being mowed too infrequently if there are piles of grass clippings left after each mowing. Consider a farmers hay field. Farmers remove close to 90% of the grass plants leaf surface when cutting hay. The grass left after the hay is baled turns a golden tan color. The color change takes place because grass plants are not capable of recovering from large amounts of stress for quite a while. The small amount of leaf surface left on the plant is not enough to maintain the physiological activities (photosynthesis) for plant energy.
Grass plants have a “growing point” where all of the leaves originate. The growing point stays near the soil surface when grass is mowed frequently. When people let their lawns grow too long, the growing point begins to elevate from the soil surface. When finally mowed, the growing point may be cut and removed with the rest of the clippings. This means death to the plant. Frequent mowing, never removing more than 1/3 of the grass blade ensures that the growing point will stay near the soil surface and the turf will stay healthy and dense, giving you the soft and beautiful look you want in your grass.