Updated: May 2018
Crush eggshells into small pieces and sprinkle them on top of the soil. Slugs, cutworms, and other insects are put off by the crunch when they crawl over the sharp edges and will leave for softer pastures. You can also toss the crushed shells into your compost heap. They break down quickly and give your plants a much-needed dose of calcium, which can help with bottom-end rot, a calcium deficiency found in some plants.
The smell of eggs will also deter deer.