Onion quality and yield in the Northwest, particularly in the Columbia Basin, has progressed immensely in the last 15 years. This is primarily due to industry performance, grower performance, and storage management. But only somewhat recently has onion quality and yield for storage produced consistent high-enough returns for growers to better understand storage and storage management. Not surprisingly, research, along with industry and grower field performance has proven the merit of thorough preparation for storage and accurate management techniques. No poor crop placed in new storage, using excellent storage management, can turn the crop into a real winner.
Unfortunately, most of you who have been growing and storing onions for some time have seen some dramatically devastating examples of what can happen in storage. So, we still cannot place immature onions harvested soaking wet and uncured into storage and guarantee problem-free results. We can, however, develop an appreciation of the necessary preparation for storage. It consists of a thorough understanding of normal weather and actual weather and good storage with the right system. This all needs to work in conjunction with having excellent storage management; which is vital for truly successful storage today. Onion storage will be successful if, decay is controlled, premature sprouting does not take place, and weight loss is minimized, all during storage.
The primary goal of storing onions is to get into the most profitable market possible. And when onions coming out of storage are in top condition, the rewards can be terrific. It all depends on four primary issues.
Summary of Primary Issues
In the next series of posts, we will cover the various issues that affect onion storage systems and the options that are available to combat these issues. Successful storage systems are available with careful consideration. Here are the four separate issues that dictate successful onion storage:
- Condition of the onions brought into storage
- Weather: Typical Vs. Actual
- Storage & System
- Storage Management
Understanding what varieties to grow for storage and how to grow them is certainly the first step. However, this article is not about appropriate varieties for storage. The specific variety of onions and their condition at the time they are brought into storage will dictate early storage management decisions. So, onion physical condition, onion maturity, and how well-cured the onions are at harvest are important “onion condition” aspects.
Successful storage management includes understanding our normal weather, and how to respond to the weather we actually get. Weather variations can have a significant effect on storage performance. A management plan from harvest through storage that takes advantage of actual weather conditions and appropriately reacting to them is an important step in obtaining optimum results. At times, this means hands-on attention to achieve peak storage performance.
The storage and system, combined with ambient outside conditions, are your tools for storage management. Understanding air volume and distribution, the control system; coupled with supplemental support equipment – such as supplemental heat, dehumidification equipment, and refrigeration, must be used in concert with outside air to maintain an optimum storage environment. A good storage management plan incorporates daily surveillance of conditions inside and outside the storage facilities to take care of the onions in storage. Conditions in storage are continually changing, and no two onion storages of the same variety are identical. An important stage for successful storage is set throughout the process of drying and curing. Since we are concerned in this article with taking onions from the field into storage, let’s begin our discussion with Onion Condition.
Primary Issue Number 1
Condition of the Onions Brought into Storage
Let’s discus the maturation of onions brought into storage. Since a mature onion will cure more rapidly than an immature onion, the date for lifting should be dependent on onion maturity. The ability to recognize onion maturity is fundamental. A mature onion is one that has stopped growing. Maturity is stimulated by stopping fertilizer application and irrigation on appropriate dates prior to lifting. During maturation, nutrients in the tops move into the bulb, which increases the onion solids content, resulting in potential increases for successful storage. Onions with higher solids have a significantly better record in storage. On the other hand, an immature onion has a wet neck. If the onion was topped prior to adequate drying, the neck provides an avenue for rot organisms to enter the bulb.
Another important fact regarding maturity has to do with respiration. The respiration rate of a mature onion is less than an immature onion, so weight loss is minimized. The date for lifting should be dependent on onion maturity. Historically, the onion crop for storage should reach maturity in the Columbia Basin sometime in late August to early September.
There is more to come in the rest of our series. Our next article is examining in-depth Primary Issue Number 2: Typical vs. Actual Weather. What the weather does on a yearly basis vs. the averages can have a large impact on what happens in the overall yearly Storage Management plan and this next section helps us dive into what items need to be considered to have Successful Onion Storage Management each year.