Does adding coffee grounds and/or egg shells really help my veggies?

You must remember different plants require different needs. Coffee grounds are only good for acidic plants.Egg shells are used generally to ward off insects.Soil amendments depend on what you have done prior to planting.

Truth some plants need nitrogen more and some need calcium more, gotta look that up for what plants you have.

The shells should be ground up (be warned, it STINKS!), but each plant needs different care.

If you grind up the egg shells and put them in vinegar your plants can get the calcium right away. Make sure to water the mixture down before putting in garden. My tomatoes LOVE it!

The egg shells will help with slugs,

Water the solution down and only put on the soil around the tomatoes.