Most vegetables are harvested when they are fresh, young, and tender, with thin skins, cells full of moisture, and a correspondingly (and understandably) short shelf life. As a result, they must be harvested right before market, handled minimally, and then sold as soon as possible. Post-harvest lifespan is limited.

There are crops that have high volumes of product maturing all at once, with limited options for immediate disposal through markets. Some of these crops have excellent long-term storage potential, provided they are sufficiently mature and are placed in appropriate long-term storage conditions.

Prior to long-term storage, most of these crops will benefit from one or more pre-harvest or post-harvest treatments that build up the product’s inherent resiliency and armor. Essentially, these processes thicken, enhance, and/or repair the outer tissue layers of the crop, allowing it to reduce the amount of moisture loss and be more resistant to attack by diseases.

Top Killing

For potatoes, until the tops die down, the skins of the tubers remain thin, loose and are easily removed. Once the tops start to die down, this signals to the plant that it has reached a stage of maturity and must now focus on setting up protective layers on the next generation, i.e. the tubers.

This same signal can be induced artificially, either by physically separating the tops from the bottoms (e.g. pulling), or by mechanical or chemical killing of the tops. Once the tops die, over the course of about two weeks, the skins toughen up, and the tubers are less prone to skinning and water loss after harvest.

Top killing can be done with weed whippers, flail mowers, or other mechanical means. Theoretically, a number of natural phenomena, such as hail, frost, or disease infections can kill or knock down the tops of the plant, however, they are not necessarily the most reliable (from a timing perspective), and they come with other complications and challenges.

Another commonly employed option for growers is to use a registered chemical top/vine killer, such as Reglone (active ingredient Diquat), to kill just the aboveground tissues, without transfer to the tubers. The focus is on killing the aboveground tissues, not the entire, living plant. Some people mistakenly apply a non-selective herbicide (such as glyphosate) thinking that this will work, however, this will kill both the foliage AND the tubers, ruining the crop.

Curing

Curing is the process of toughening the skins or drying down the outer layers of the produce. It has several purposes, including:

  • Reducing and minimizing water loss
  • Reducing or preventing wounding, bruising, or skinning
  • Reducing or preventing attack by pathogens (at or after harvest)
  • Encouraging natural wound healing to take place

Curing will start as soon as plants reach a certain stage of maturity, with tops starting to fall over and barriers begin to be formed between the actively growing foliage and the long-term storage organs.

Curing involves placing harvested product in a warm, dry location to cure for two to three weeks. Temperatures should be in the mid-teens (15-18°C). Once curing is completed, product can be bulk piled, and temperatures can be gradually lowered by 1 degree a day until a final long-term storage temperature is reached.

In bulb vegetables, such as onions and garlic, you will see the outer wrapper and scale leaves start to tighten and dry down, as well as neck areas start to constrict and tighten up. Once about 50 percent of the leaves have started to fall over in onions, depending on where you are located and how much growing season is left, plants might be lifted, windrowed, and/or pulled. If conditions are warm and dry, plants can be left in windrows in the field for a time or can be cured in a covered location.

Potatoes also benefit from a period of curing. Even with careful handling during harvest, some skinning and bruising will likely occur. Warm conditions will encourage wound tissues to form, effectively sealing off wounds and dramatically slowing moisture loss and blocking infection by pathogens.

Winter squash and pumpkins are often cured prior to long-term storage and sale. Curing toughens their outer tissue layers and dries up stalks to reduce water loss. Dry curing conditions also help to prevent diseases from getting a toehold and allow some ripening to occur.

Conclusion

All these processes can dramatically improve the post-harvest prospects for long-term storage crops, provided they are adequately matured and in good health/condition. These post-harvest processes are suitable for bulb vegetables, vine crops (i.e. cucurbits) and tubers.

It should be noted that crops that have been frozen, diseased, or damaged at or prior to harvest will have limited post-harvest lifespans and should be carefully graded to only work with the best quality product. No amount of curing can fix a garbage-y crop.