Onion Rot and What To Do About It.

Onion rot is a frustrating thing. Once more I planted, I weeded, I watered (some), and I harvested.

Two bags of onion sets went into the ground. One yellow Spanish, one white onion. And they grew, albeit slowly due to a dry spring.

They were smaller than usual by harvest time, but I had planted more than necessary, so I figured we should still have enough for our family of 7.

Late summer rains made up for lack of spring rains, and the onions got too wet.

At last I finally made the time to go, pull them out, and spread them out on a makeshift table in an old ‘airy’ shed. Then forgot about them for a couple weeks.

Finally I realized winter was fast approaching, so I went to properly store them. Well, guess what?

Approximately half of my onions were rotting!

Disappointed, I nevertheless saved what I could and took them in. There weren’t a whole lot left, and I knew I would use them up fast enough.

But they continued to rot.

Each time I went into our furnace room, a couple more were soft.

This wasn’t a new problem. Fall 2019 seemed especially bad, but I always have a bunch of onions I end up throwing away. What am I doing wrong?

So I googled and researched. And talked to a neighbor lady.

Now I am armed with some tips and suggestions for next year.

So if you’re struggling with the same thing, let me share. And I’ll let you know if these things worked for me.

Onion soft rot is a common problem that affects onion crops worldwide.

It is a condition caused by various bacteria, including species in the genera Pectobacterium and Burkholderia, which lead to the decay and deterioration of stored onions.

You might notice your affected onions becoming soft, mushy, and emitting a foul odor, which are classic signs of this issue.

The disease often occurs after harvest, like it did for me, but the infection can start in the field, emphasizing the importance of diligent farming practices and careful handling.

Understanding the factors that contribute to the development of soft rot in onions is crucial to managing and preventing this condition.

High humidity and temperatures, along with mechanical injuries, provide perfect conditions for the bacteria to enter and colonize the onions.

Once the bacteria get established, they break down the firm cell walls of the onion, resulting in the characteristic soft, squishy texture.

Your best practices for preventing soft rot include proper field sanitation, careful handling during harvest, and optimal storage conditions.

My biggest mistake was not watering them during a dry spring.

They need the right water amount, at the right time. The wet late summer we had didn’t help, but there was nothing I could do about that.

Causes of Onion Soft Rot

Onion soft rot is mainly caused by certain bacterial species, specific environmental conditions, and various agricultural practices that inadvertently promote disease.

Bacterial Pathogens

The primary culprits behind onion soft rot are bacteria, particularly Pectobacterium carotovorum subsp. carotovorum and Pectobacterium subsp. atrosepticum.

These pathogens forcefully enter the onion tissues, producing enzymes that degrade cell walls causing the characteristic softening and rotting.

Environmental Factors

High temperatures combined with excessive moisture create an ideal environment for the bacteria to thrive. If your onion storage or field has poor ventilation, this can make the problem worse, leading to widespread soft rot.

And once it’s in your soil, its time to move on to a different location.

Gardening Practices

If you damage your onions during harvesting, handling, or storage, the bacteria get easy access to the onion tissues. Most often I don’t find this a problem, but it could be if you use mechanical devices to harvest.

Soil that is not well-drained can also harbor bacteria, adding to the risk of soft rot if onions are left in the garden too long after maturity or if overhead irrigation is used excessively.

Management and Control

Effective management and control of onion soft rot involve a combination of cultural practices, chemical treatments, and biological control methods.

By integrating these strategies, you can significantly reduce the impact of the disease on your onion crops.

Tips on Preventing Onion Rot in the Great North.

To prevent onion soft rot, you should start with good sanitation and field selection. Choose well-drained gardens and avoid places with a history of soft rot.

Regularly rotating your crops with non-host plants every 3-4 years can also help to reduce pathogen carryover.

1. Make a raised bed, before planting.

This should help with water drainage. Your onions need moisture, but not too much. If you live in a wet area, this might be a good idea.

Note: In 2022 we moved to a different farm and I have had no trouble with growing onions in a garden bed. We had a very wet summer, and they still did great. A lot of it has to do with your soil.

2. Plant in a different location.

Bacterial Soft Rot can infect the plants when it gets too wet, and once it’s in the soil, it’s hard to eliminate. Practice rotating your crops to reduce pathogen carry over.

3. Water more diligently.

Especially at the beginning. Onions like water at the beginning of the growing season. Water your onions at a rate that matches their needs, avoiding excess moisture that can foster fungal growth.

4. Harvest at the right time.

This is way earlier then what I usually do, and might be a big part of my problem. I usually wait ‘til September… We live in zone 2, so our growing season is short. However, smaller onions are better then none at all!

However, harvesting them too soon can also increase the chances of them rotting. If they aren’t mature enough, they are more susceptible to soft rot.

I’m concerned that they won’t have grown much by then, but maybe if I water diligently, they will be be bigger.

5. Dry in the sun 1-2 days, but don’t let them get rained on.

Curing them properly is also helpful. Dry them in an airy shed, if possible. Keep them in there for 7-14 days. After this, cut off the dried tops, then store them in boxes, in a warm, dry location.

I usually store mine in our furnace room.             

We’ll see what next year will bring. If you know of any tips on growing onions, please share. I’m always willing to learn.

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