Your lawn is full of small, pointed objects, and at some point your lawn mower is sure to run over all of them. Occasionally, a small rock or a twig will be sucked into the mower and ejected at a high speed into the mower bag, puncturing or ripping it. It is important to repair the tear immediately before it becomes too large to fix.
Cut a piece of denim or canvas from jeans or cargo pants you no longer wear to use as a patch. The piece should cover the tear with a 1-inch margin on all sides.
Lay the bag on a flat surface, such as a workbench. The outside of the bag should be against the bench top, with the inside visible.
Place permanent fabric glue on one side of the patch. Place the patch carefully over the tear from the inside of the bag. Hold the two sides of the tear together so that there is no gap between them as you place the patch over it.
Lay a flat, heavy object over the patch. Keep the patch in place for as long as recommended by the fabric glue instructions.
Remove the flat object after the appropriate time and test the patch by gently tugging at it. If it holds well, the bag can be reattached to the mower.