The Love and Layers of Onions

Sep 27, 2019

By T. Eric Nightingale, U.C. Master Gardener of Napa County

Until recently onions were, for me, a smelly vegetable I liked to put on hamburgers. I have recently learned, however, that they have a much more colorful history. Despite their checkered past, many people today credit onions with near-magical abilities.

A little online research will turn up dozens of sites proclaiming the health benefits of onions. Among the purported benefits are lower risk of cancer, heart disease and hypertension; better maintenance of blood sugar; and an enhanced immune system. While these claims have varying degrees of verifiability, one thing is certain: people love onions.

Claims regarding the power of onions are nothing new. Onion cultivation goes way back, about six thousand years or so, and likely began somewhere in Asia or northern Africa. There is evidence of onion obsession in almost every civilization and situation possible.

Onions have been used to treat a variety of medical ailments including indigestion, blisters and even dog bites. They were thought to make warriors stronger and to induce romantic feelings, and they were sometimes used as a currency to pay rent.

Ancient Egyptians held onions in high esteem, believing their concentric rings symbolized eternal life. Artifacts found in tombs appear to be onions fashioned from gold.

On the more practical side, onions were easy to grow, transport and store, making them an ideal food for people in a variety of climates. They quickly spread around the world and became a staple of many cuisines.

Onions are a great source of vitamins C and B, potassium and fiber. Researchers investigating the onion's cancer-fighting abilities have focused on quercetin, a type of antioxidant contained within the onion bulb.

When most people speak of onions, they are usually referring to Allium cepa, the common onion or bulb onion. This species is a large, round bulb that may be white, yellow, purple and red. All species within the genus Allium are often considered onions, taxonomically. Among these are garlic, leeks and chives, as well as a number of ornamental plants. All these plants share similarities in leaf shape, flower appearance and bulb formation. Of course, they also share that particular pungent smell and flavor.

The unique flavor of onions and their kin is due to enzymes in the bulb. An uncut onion bulb emits no smell. But when damaged or cut with a kitchen knife, the plant cells release enzymes that combine to form sulfur compounds, source of the strong, distinctive odor. A separate enzyme produces the acidic fumes that bring tears to the eyes of chefs the world over.

Onions probably evolved to have these intense favors and smells to deter ground-dwelling mammals that would otherwise see the bulbs as a tasty lunch. Humans enjoy the pungency, however. Just look at the booming hot pepper industry.

If your home-grown onions don't have enough of that “oniony” flavor for your liking, your plants may be suffering from a sulfur deficiency. Sulfur is so important to the health of many crops that some call it “the fourth macronutrient” (after nitrogen, phosphorus and potassium).

In Napa Valley, it is unlikely that your soil is deficient in sulfur, but the plants may not be absorbing the nutrient. To be accessible to plants, sulfur must be converted into sulfates through the decomposition of organic matter by soil organisms. You can increase the organic matter in your soil by adding manure, compost or mulch. Growing cover crops and tilling them in when they reach the end of their season is also an option. Of course, it is also possible that the onion variety you purchased was a mild one, so always try a few different types.

While growing onions is not difficult, you should note a few things before beginning. Always read the information on the seed package or set package. Some onions need to be consumed quickly after harvest, while others can be stored through winter.

Another difference is between short-day and long-day onions, referring to the amount of daylight hours the plants will receive. Plant short-day onions in fall for harvest the following spring. Plant long-day onions in early spring and harvest in summer. If you are unable to determine which type you have, look at the recommended climate zones. Short-day onions are suitable for warmer climates such as zone 7 and up.

It is pleasing to know that, when growing onions, we are participating in an activity that humans have engaged in for millennia. These connections remind us of our place in history and our responsibility to the future. That said, onions taste pretty good, too.

Fall Faire: U.C. Master Gardeners of Napa County's second annual Fall Faire will take place on Saturday, October 5, from noon to 4 p.m., at 1710 Soscol Avenue in Napa. Tickets are $5 for adults. Children 15 and under are free with an accompanying adult. Purchase tickets online with a credit card. Cash and check only will be accepted at the door. Find more on the Fall Faire at

Next workshop: U.C. Master Gardeners of Napa County will hold a workshop on “Stinking Roses and Edible Alliums: Grow These Essentials for Your Kitchen” on Saturday, October 12, from 9:30 to 11:30 a.m., at the University of California Cooperative Extension, 1710 Soscol Avenue, Napa. For more details & online Registration go to or call 707-253-4221.

The UC Master Gardeners are volunteers who provide UC research-based information on home gardening and answer your questions. To find out more about upcoming programs or to ask a garden question, visit the Master Gardener website ( or call (707) 253-4221 between 9 a.m. and noon on Mondays, Wednesdays or Fridays.