Garden Docs: What makes an onion sweet?

Lori C. of Santa Rosa asks: I am curious as to what makes an onion sweet and what makes them pungent?

Answer: According to the largest and oldest onion plant farm in the U.S., Dixondale Farms in Texas, sweetness in the onions is another way of saying that they lack pungency and are relatively mild tasting.

Believe it or not, sugars have nothing to do with it. Some pungent onions actually have more sugar in them than sweet onions, but the sugar is masked by a high amount of sulfur compounds.

Pungency is the primary factor that determines onion sweetness and is genetic, relating to the pyruvic acid level. The pyruvic acid content of storage onions ranges from 10 to 13 percent, while it is below 5 percent in sweet onions.

Growing conditions will also affect pungency levels in onions. Triggers such as high temperatures, drought and insects will increase the pungency, thereby decreasing the sweetness of the onion..

All onions need sulfur for proper growth, but the sweet onions contain far less sulfur than the pungent onions. The low amount of sulfur in sweet onions allows the sugar flavor to come through. Sulfur helps the plants take up nitrogen and fight off pests and disease. Most of the onion’s sulfur uptake occurs during the latter part of the season during the bulb’s growth.

The peak of the onion’s sweetness occurs when the onions are harvested. Over time, the pungency increases. When preparing onions for meals, it’s best to harvest and cut them as close to cooking time as possible to get the best flavor.

Janice N. of Santa Rosa asks: What is the difference between softwood and hardwood cuttings?

Answer: Softwood, or green tip cuttings as they are most commonly called, are by far the most popular way to propagate plants. This method is used quite often in the propagation of annuals, perennials, herbs and vegetables as well as many varieties of houseplants.

Softwood cuttings are usually taken in the spring. But those who have a greenhouse, cold frame and indoor grow lights, can root softwood cuttings throughout the year.

Semi-hardwood cuttings are best for deciduous and evergreen plants, and many perennials. These particular cuttings are firmer than the softwood cuttings and they can usually survive more abuse if not cared for properly. Semi-hardwood cuttings are most commonly taken between late summer and early winter.

Hardwood cuttings are most often used in propagating deciduous shrubs and trees and are most commonly taken during the winter months when the plant is dormant. Many plants that are propagated with hardwood cuttings can also be reproduced through semi-hardwood cuttings. However, because of the lack of foliage and growth activity in the hardwood cutting, propagation via this method requires little, if any, environmental control, so therefore, this type of cutting makes it easy for growers who don’t have a greenhouse, or have access to one, or any other type of propagating device.

Lauren P. of Windsor asks: What is the difference between an open-pollinated seed and a hybrid seed?

Answer: Open-pollinated seeds are those, which if properly isolated from all other varieties in the same plant species, will produce seeds that are genetically “true to type.”

This means that the seed will result in a plant very similar to the parent, meaning, the seed from which you started.

If open-pollinated varieties are allowed to cross within the same species, the resulting seed will be a hybrid. So seed from a hybrid variety can be saved, but when sown, will not be true to type, meaning it will not be the same thing as what you grew.

Dana Lozano and Gwen Kilchherr are garden consultants. Send your gardening questions to The Garden Doctors at pdgardendoctor@gmail.com. The Garden Doctors can answer questions only through their column, which appears twice a month in the newspaper and online at pressdemocrat.com.