Egg carton cups are already spaced evenly, and paper cartons break down in the soil. That makes them a handy way to line up onion sets in a tidy bed. Here's how to use the trick, along with the planting rules that matter most. Why Try the Egg Carton Method? Home gardeners use plain paper or pulp egg flats as a simple planting grid. A standard 30-egg flat has cups about 2 … [Read more...] about Plant Onions in an Egg Carton Grid — The Easy Spacing Trick (and the Extension Rules That Make It Work)