how deep do you plant onion bulbs
Preparing the Soil. Soil is best prepared for planting onions by mixing in 1 1/2 inches of compost or by adding 10-20-10 fertilizer in a trench. Dig the trench 4 inches deep, add 1/2 cup of fertilizer for each 10 feet of row, cover with 2 inches of soil and plant your onion sets on top of that.ou can grow onions in U.S. Department of Agriculture plant hardiness zones 3 through 9. Onions are a cool-season crop. If you live in a Mediterranean climate, it's best to plant what are called short day bulbs in the fall. They will only harmed if temperatures drop below 20 degrees Fahrenheit.