Onions prefer loose, well-drained soils that are high in fertility, slightly acidic (pH between 6.2-6.8), adequately irrigated and in full sun. The looser the composition of your soil, the larger your onion bulbs will grow. Prepare your bed by turning under animal manure or compost, making sure that it is fully broken down before planting. Compost composed of cedar or redwood is not an acceptable substitute for high-quality compost.
Onions are heavy feeders, so provide plenty of nitrogen and phosphorus. A good rule of thumb is to add one cup of equal parts blood meal and bone meal every 10 feet of row.
Planting & Growing Onion Transplants
The potential for fungal diseases like downy mildew and pink root can be greatly reduced by avoiding beds where onions, garlic, and other alliums have been grown within the last two years. This time period is a basic rule of thumb but, in general, “the longer the better”.
As gophers are a major pest in onion beds, use gopher traps, wire barriers or wire baskets prior to planting.
We ship Onion Transplants in the fall as this is the optimum time to plant in mild climates. Onion Transplants are often wilted when they arrive, but like other members of the hardy lily family, they will survive for about 2 weeks after being pulled from the soil. If you cannot plant them immediately upon receipt, either refrigerate them after soaking the roots in water or mound soil around the roots and keep them moist until planted.
Before planting, trim the tops to approximately 3” and roots to 1/4” – roots will begin to grow rapidly once planted. Plant onion transplants 1 – 2” deep and 4 – 6” apart. Plant close as 3” apart if smaller onions are desired. Rows should be 18 – 24” apart or 12” apart if planting for commercial production.
If planted on raised beds which are approximately 20” wide, transplants should be planted in double rows 2 – 4” from each edge. “Scatter planting” among vegetables in inter-planted gardens is sometimes utilized to ward off a variety of pests, but onions must not be forced to face heavy competition from surrounding neighbors. See our article on Companion Planting for Onions for more information.
Apply a layer of mulch such as straw, to help maintain moisture and protect the plants during the winter. Onions are hardy to 20°F, but in cold climate regions, protect your plants with a thicker layer of mulch (at least 2 inches deep).
Onions are easy to grow from sets. Keep in mind though, onion sets perform the best in long day growing regions. Plant 1” deep and 1-3” apart. Harvest young plants for use as scallions, thinning to 3-4” spacing. Onions should be mulched and supplied with ample phosphorus while growing.
Mulch deeply (up to 8”) in cold winter areas but only lightly in milder climates. Mulching will suppress weeds, maintain soil moisture and protect bulbs from “heaving” (working their way out of the soil) during extreme temperature cycles.
Weed suppression is critical for onions – you can grow weeds or onions, but not both. Regular irrigation is necessary anytime rainfall is not sufficient to provide the 1” of water per week required to keep bulbs from splitting in hot dry soil or tasting bitter at harvest. Water up until the time you harvest!
Beds kept weed free and properly irrigated will require little additional care.
Harvesting & Storing
When the top of an onion turn to yellow and begin to fall, it means that your onions are mature enough to harvest. Use your hand or a rake to bend the tops of those that haven’t completely gone. The purpose is to save all the energy for onions rather than wasting some on the leaves.
When the tops turned brown, you can harvest the onions. To secure them from sunburning, place the tops of each row over the bulbs of another row. When the outermost skin gets dried, which can take 10 to 14 days, clip the roots and wipe off any soil remaining on the bulbs.
For storage, it is always best to keep them separated. An individual foil wrapped onion can stay up to one year in a refrigerator. The type of onion also matters like pungent onions contain less water and they can last longer than sweet and moist types. The recommended method of storing onions is hanging an onion is mesh bag, at cool, ventilated, and dry location while ensuring that onions stay separate from each other.
Let’s plant the onion in the upcoming fall and have a fresh, natural, organic, home-grown onion yield next summer!
Read original article here: http://www.groworganic.com/organic-gardening/articles/How-to-Grow-Onions