Onions can be grown using three different methods. You can plant seed directly planted in the ground or in starter trays. Onion sets, which are small dry bulbs of onions, can be planted at the first sign of spring. Alternatively, you can use onion seed starts, which include the green leaves, and which can be purchased wherever garden vegetables seedlings are sold.
Prepare the garden space by tilling the soil and adding 1 to 2 inches of compost to the area. Retill to mix the compost into the soil.
Create rows in the garden space, using a hoe, approximately 1 foot apart and 1 1/2 to 2 inches deep for scallions and 1/2 inch deep for large onions.
Place the onion seed starts into the row at intervals of 1 inch apart for scallion-sized onions and 4 inches apart for large onions.
Use the garden trowel to cover the onion seed starts, keeping the green sections of the seed starts upright in the row.
Harvest scallions in approximately 30 days. Bulb onions will take approximately 90 to 120 days to mature. The green tops of the onions will turn brown and fall over when the onions are mature.