Part two in a series by organic-lawn-care guru Glenn.
MYTH: "If I mow short, it will be longer until I have to mow again." False! Your grass needs grass blades to do photosynthesis (convert sunshine into sugar) to feed the roots. When you whack the blades off, the grass has to RACE to make more blades to make sugar. It then grows amazingly fast. This fast growth uses up a lot of the grass's stored sugar, and weakens the plant. It is now vulnerable to disease and pests! Tall grass is healthier and can use the extra sugar to make rhizomes (more grass plants) thus thickening the turf. Have you ever noticed that short grass in the summer is always riddled with dead brown patches?
If you have a serious weed infestation, consider mowing twice as frequently as you normally do. The sensitive growing point for grass is near the soil. The sensitive growing point for most weeds is near the top of the plant. So when you mow, it's as if you are giving your grass a haircut and cutting the heads off of the weeds.
Finally, when mowing, be sure to leave the clippings on the lawn. It adds organic matter and nutrients back into the soil. If you don't leave the clippings, your soil will begin to look more like "dirt" than soil. Soon it will be a form of cement that nothing will grow in and you will have the world’s most pitiful lawn. Some people are concerned about "clumping" - that only happens when you mow too short or when you don't mow often enough. A dedicated mulching mower is recommended. The blade and deck are designed to cut and re-cut the clippings and then blow them into the turf so they form an almost invisible source of nutrients.