Most onion diseases are related to excessive moisture

Kate Russell

Autumn is the best time for Gilroy gardeners to plant onions, scallions, and shallots.

Onion bulbs are classified by color: white, yellow, or red. Those bulbs occur when shortened underground stems are surrounded by fleshy leaves, called scales.

Scallions are a type of onion selected for smaller bulb size. Immature onions are also used as scallions. Shallots, once considered a separate species, are now know to be an especially mild variety of onion that grows more like a garlic. Onions are also classified according to the number of day-hours it takes to trigger bulb development. Long-day (L) onions need 14-plus hours of daylight and are not suitable to Gilroy gardens. Indeterminate-day (I) onions need 12 to 13 hours and may work in our area. Short-day (S) onions need 11 to 12 hours and are the best choice for Gilroy gardens.

Onions are slow starters and don’t handle weeds very well. Plant onion seeds 1/4-inch deep and 1/4-inch apart, and then thin with mature plant size in mind. Scallions do not need to be thinned. For better results, plant “sets.” Onion sets look like baby onions. Do not use grocery store onions to start because those plants may carry long term pest or disease problems.

Onions can grow in direct sunlight or partial shade. They prefer soil pH from 5.0 to 6.8. The one thing onions cannot tolerate is poor drainage. They have a shallow root system, so regular irrigation and weeding are important. They are heavy nitrogen feeders, so blood or alfalfa meal can be applied, depending on the results of a recent soil test.

Onion maggots, onion flies, thrips, nematodes, onion eelworms, and gophers all feed on onions. Most onion diseases are related to excessive moisture. Allowing the soil to dry out between waterings will prevent many onion diseases.

Onions mature in 12 to 18 weeks. When the top half turns brown, stop watering. When the lower stem turns yellow, carefully dig them up and brush off soil. They should now be braided, laid flat, or placed in nets for several days to dry. Cured properly, onions can be stored for up to six months.

Leaving some onions in place to complete their life cycle, you can collect offshoots and seeds for next year. Also, onion flowers attract many beneficial insects, such as hoverflies and parasitic wasps.

Once established, the upper portion of scallions can be snipped off, leaving the base and roots in place to regrow. But cutting onions can be problematic.

Onions use chemical warfare to protect themselves, releasing an acid gas when cut. And none of the popular tips work: bread in your mouth, sunglasses, lemon juice … nada. If you need respite from onion burn, freeze or refrigerate your onions before cutting or cut them in front of a fan.

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Kate Russell

Kate Russell is a UCCE Master Gardener of Santa Clara County. She wrote this for Morgan Hill Life. Visit the website
Kate Russell
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