Many issues come to light when we are talking about proper onion storage management. Please read our article by CLICKING HERE if you are interested in getting caught up. The next issue that growers face can vary significantly from year to year with a new normal being established all the time. Considering historical as well as current patterns in the weather will be very beneficial for a successful crop and storage season.
PRIMARY ISSUE 2:
Weather: Typical Vs. Actual
The market calls for onions (coming out of storage) shortly after fall harvest in September all the way through March, in the Columbia Basin. Since weather plays such a huge part in successful onion storage, we should do our best to understand the weather during this part of the year. It’s also wise to thoroughly understand the chemistry between the actual weather and storage operation/functionality. By doing this, growers can maximize storage performance and run more efficiently. The complete storage management plan should be based on typical weather for field and storage vicinity, coupled with the storage and system capability. An example of a storage management plan, based on typical Columbia Basin weather will be discussed in a later in the Storage Management issue.
Below is a plot showing “Average Low Temperature” and “Average High Temperature” in the Columbia Basin. Keep in mind, that actual weather can be both higher and lower than the average temperature is shown in the plot below. In addition to temperature, outside relative humidity will also dictate storage management details and system operation. For now, we’ll focus on temperature.
Typical weather in the Columbia Basin allows superb field curing during the month of August, and often through September. So, lifting of onions for storage in the Columbia Basin can take place at this time. A well-cured onion sets the stage for successful storage. So, how much time is required for field curing? The time necessary to properly field cure is dependent on onion maturity and weather. If the onions are mature when lifted, and normal Columbia Basin weather prevails, field curing takes between one and three weeks. A dry, well-cured onion brought into storage from the field with minimum physical damage is a big first step toward successful storage. Weather and harvest schedule often prevent completion of the cure in the field. Consequently, curing must be completed in storage.
The benefits of a properly cured onion include:
- Maximum retention of outer scales
- Protection against decay.
- Protection against early sprouting.
- Assures minimum weight loss.
The outer scales have natural-occurring anti-fungal compounds. Since the neck rot fungus is a major concern in storage, retention of the outer scales is an important benefit of the cure process. Fortunately, Columbia Basin weather is usually superb for curing in the field. Here are several benefits to curing in the field:
- If curing must be completely accomplished in storage, excellent air distribution and a lot of air is required. How much air? A general rule is 2 CFM/cubic foot of onions. 2 CFM/cubic foot of onions is approximately 110 CFM/ton of onions. That is more than five times the airflow used in today’s potato storage. Very few onion storages in the Columbia Basin have the ability to actually supply 2 CFM/cubic foot.
- August often provides warm-enough weather to get the temperature of the bulb into the middle 80’s, or even 90°F for several days. If this can be accomplished neck rot fungus will be significantly controlled.
- The high temperatures during early storage necessary to complete the cure process will be minimized and require less supplemental equipment help like heat from large burners and dehumidification.
The real message, here, is choosing a variety for storage that will reach maturity in August, make certain that the crop does mature in time to accomplish a major portion of the cure process in the field and reduce the requirement for completion of cure in storage.
Stay tuned for our next article showing the importance of the Storage & System used to fully cure and effectively storge properly cured onions.