Yellow Sweet Spanish Onion

Onions require well-draining soil with a pH of 6.0-7.5 and full sun exposure for at least 6-8 hours per day. The soil should be rich in organic matter, such as compost, to promote healthy root growth and ample nitrogen for leaf growth. They prefer loose, loamy soil that retains moisture but does not become waterlogged. The life of an onion can be divided into two phases: a vegetative growth phase and a bulbing phase, which is initiated when the daylength reaches a pre-programmed duration. Those wishing to get the largest bulbs possible should aim to get the plants as big as possible before that day arrives. Keys to achieving this include finding a variety that is well-suited to your geography, starting seeds early and setting out as soon as possible, fertilizing, and most importantly, keeping the onion patch as weed-free as possible. By following these steps, it is within any gardener's ability to go from an onion seed to a one pound or larger onion in one growing season.

Start indoors 8-12 weeks before last frost.  Sow seeds 1/4" deep in well moistened seed starting mix and cover with a plastic dome.  Set in a warm place and keep moist until germination has occurred (7-14 days).  Once most of the seed has germinated, remove the plastic top and give plants access to light (if not already) Trim tops down when they reach 4-5" to prevent them from becoming tangled. 

After 4-6 weeks, transplant seedlings, either into the garden or into an intermediate container.  In new location, poke a 2-3" deep hole in the soil with a pencil, carefully tease apart seedling from tray and lower the seedling into the hole, burying 1/4" of stem.  Final spacing should be 4-5" between plants with rows 18" apart.  Fertilize regularly in spring and early summer.

Insect Pests

Although not a problem for most gardeners, onion maggots are the predominant threat to onions and can cause stunted growth and even death of young plants. To prevent and control these pests, it's recommended to rotate crops, remove any infested plant debris, and use insecticidal sprays or dusts as needed. Sticky traps placed near the base of plants can also be used to monitor and trap the adults.

Diseases & Other Problems

Onions are generally very healthy and easy-to-grow, at least once they're established, however there are some keys to getting them off to a good start. When working with young seedlings, it's important to keep the tops trimmed, lest you end up with a mess at transplanting time. Young seedlings also need to be kept well-watered after transplanting and may benefit from some temporary shade until they are established. Finally, weeds need to be kept at bay as they can rob vital nutrients from the young plants. Pulling weeds from a patch of small onions can be quite challenging if the weeds are allowed to get much larger than the onions.

Onions can be harvested at any time for fresh eating or cooking. Onions that will be stored need to reach full maturity before harvest. For storage onions, wait until at least half of the tops have fallen over, then pull the remaining plants. Allow them to dry in a warm, dry, and well-ventilated area for 1-2 weeks until the outer skins become papery. Afterward, trim the roots and (optionally) cut the stems to 1 inch, remove any damaged or diseased layers, and store them in a cool, dry, and dark place with good air circulation, such as a mesh bag or crate. Check the storage recommendations for your variety and use or freeze before the onions have spoiled. Some varieties may last 6 months or more in storage while others, particularly the very large varieties, may store for only one month.

CONSIDERATIONS:

Onions are inbreeding plants that require a vernalization period to produce seed. Although distinct from bunching onions, the two species do occasionally cross and should be separated by at least a mile if two seed crops are being produced simultaneously. Alternatively, different varieties may be caged to prevent cross pollination by insects. Plants should be mulched or brought indoors in areas with harsh winters.

HARVESTING SEED:

Plants will flower and produce seed in the second year. Onion seeds are prone to shattering (falling off the plant) so they should be harvested as soon as the pods start to dry To harvest seeds, place mature heads over a bag or bucket and clip the head from the stem. Place the heads in a paper or cloth bag and crush to release the seeds. Winnow and store in an airtight container until ready to use.

SEED LONGETIVITY:

Onion seeds will remain viable for two years when stored under ideal conditions.