What Makes Onions Bulb?

Have you ever planted onions, only to be disappointed in the size of bulb produced, or even have no bulbs produce at all? Here are some guidelines to ensure bulb production of onions in your garden.

Choose the right variety: onions are characterized by the length of day required for them to produce bulbs.

“Long-day” varieties will quit forming leaves and begin forming bulbs when day length reaches 14-16 hours. These varieties do better in the NORTHERN STATES. They are often the little onion “sets” you find at the box stores.

“Short-day” varieties quit forming leaves and begin forming bulbs when the day length reaches 10-12 hours, and are best for Southern Gardens. We recommend 1015Y, Texas Legend, and Southern Belle Red for Central Texas.

Set out onion transplants that are ¼” in diameter or less. Onions will bolt (flower) if plants are larger than ¼” in diameter and are exposed to prolonged temperatures below 45°F. When bolting occurs, bulb size, quality, and storage are reduced.

Plant at the right time: The ideal time to set out transplants is 4-6 weeks before the average frost free date for your area. In Marble Falls, March 15th is our average frost free date. The plants will then be about optimum size at the same time, and the day length is sufficient to induce bulbing. Setting transplants out too early may result in plants being too large when exposed to prolonged temperatures below 45°F, and plants will bolt before producing bulbs. That said, because our winters are so variable in Central Texas, some years you will be more successful than others whether you plant early or late!

Fertility and moisture influence the thickness of the “rings” in the bulb. The old adage is that for each leaf, there will be a ring of onion, and the larger the leaf, the larger the ring will be. The goal is to produce as many healthy leaves as possible before the bulbs set. Pay attention to fertilizer applications, as onions respond well to fertilization, and water to a depth of 6” on a regular basis.

Following these guidelines should put you on the road to success in producing large onion bulbs!

By |2017-12-11T10:53:43+00:00December 11th, 2017|Plants|

About the Author:

Mary Kay is an asset to Backbone and a wealth of knowledge! Many customers come in and ask for her by name for all their plant questions. It's no wonder why, as Mary Kay has 43 years of experience in the horticulture field. She holds a B.S. in Horticulture from Ohio State University, and a TMCNP and a TCLP from Texas Association of Nurserymen, and a Specialist in Urban Trees Certification from Texas A&M.