keep shells in open container in fridge. When full, crush shells into small bits and sprinkle around base of plants. Sharp eggshells will deter slugs, snails, and other bugs from nibbling on garden and add touch of calcium to soil.
All you need is a small amount of vertical space around a balcony or an open window which can hang or store a vertical array of drink bottles that can grow all your herbs and lettuce easily. Recycle as many of your plastic drink containers.
Save your large egg shells next time and plant with seeds. Once plants are large enough, just transfer the whole egg into the ground. The shell is actually a great fertilizer and the roots will be able to break right through.