Onion/Leek transplants are a really easy way for you to grow onions in your garden. You can break apart the individual cells of the 6 packs and plant out the onion seedlings six inches apart in a richly composted soil. Prepare the bed with an inch of horse manure, and enough landscape mix and worm castings to completely color the ground, first green, and then black. Use any finger to poke a hole into the ground and then plant an onion into that hole. Usually onions take up to half a year to mature, however, you can harvest the developing bulbs at any time, prior to maturity and you will still get that great onion flavor but just not have the size that really matters. As you plant each onion seedling, add a fistful of landscape mix and worm castings to the soil.