Propagating Onions

Seeds

• Depending on the type of soil in your garden, you might be able to plant onions directly into your garden from seed. According to Clemson Cooperative Extension, onion seeds can be planted in groups of eight to 12 per foot of row. Cover the seeds with about 1/2 to 3/4 inch of soil and space the seeds about 2 inches from each other. If you live in an area with a short spring growing season, you might be better off planting green onions than bulb varieties, according to the University of Minnesota Extension.

Sets

• You can also use onion sets to establish an onion planting. Sets use young seedlings to speed up the growing process. However, according to the Clemson Cooperative Extension, they can be more expensive than other types and need to be planted at just the right time in order to become established and produce healthy bulbs. Select sets that are no more than an inch in diameter for best results. Ensure that the sets have not sprouted and plant them about 1 1/2 to 2 inches beneath the soil.

Transplants

• If you want large, dry onions to use for slicing, then propagation with transplants is the best way to go, according to the University of Illinois Extension. Transplants are young onion seedlings that can be kept indoors to give you a head start on the growing season. To put transplants in the garden, place the plants about 1 to 1 1/2 inches in the soil and space them 2 to 3 inches apart. You can also grow your own transplants by starting seeds indoors. Keep the seedlings inside about eight to 12 weeks before you plant to transplant them into your garden.

Soil Preparation

• Regardless of the propagation method you use, prepare your soil before planting onions. Most varieties prefer well-drained, fertile soil sites with a pH between 5.5 and 6.5. Onions are sensitive to acidic soil conditions, so use soil amendments to increase soil pH if necessary. For best growing results, obtain a soil analysis from your local university extension office. A lab test provides a thorough analysis of your soil's pH and nutrient profile.