Growing from the wrong end

Why Doesn't Cutting Grass Kill It?

Almost every plant grows from its tips. Grass grows from its base, which is why mowing it does no harm.

You are cutting the oldest part, not the growing part.

Step 1 of 5

Cutting the top off most plants is serious.

A bean or a sunflower does its growing at the very tip of each shoot. Snip that off and the plant has lost the place it was growing from.
Step 2 of 5

A blade of grass grows from the bottom.

The growing zone sits at the base of the leaf, down at ground level, and pushes the blade upwards. The tip is simply the oldest part, riding along.
Step 3 of 5

So a mower takes the part the plant is finished with.

Cut a lawn and you remove old leaf while the growing zone stays safely below the blade. By the weekend the grass has pushed more leaf up through.
Step 4 of 5

The same trick is why grazing animals have anywhere to graze.

Sheep and cattle crop grass to the ground again and again. Any plant that grew from its tips would have been eaten out of existence long ago.
Step 5 of 5

It is why grasses cover so much of the world.

Prairie, savannah, steppe and every lawn are grass, and so are wheat, rice, maize and barley. Those first three alone supply about half the calories humans eat. Surviving being eaten turned out to be worth a great deal.

Grass also spreads sideways by runners, so one plant can quietly become a whole patch without ever setting seed.

The short version

Grass is unharmed by cutting because it grows from the base of each leaf rather than the tip — so mowing and grazing remove only the oldest part.

Mark a grass blade with a pen halfway up, then look in a few days. The mark has moved upwards, because the new growth came in underneath it.