Do your carrots wilt, your potatoes sprout and your squash pucker and shrink? If so it could be from improper storage. Ruth Hazzard, Extension agent at University of Massachusetts, shared her experience with root crop storage and Lee Stivers of Pennsylvania State University Cooperative Extension spoke about Vegetables’ Post Harvest Needs at the New England Vegetable & Fruit Conference in December, 2011.
Long term storage is successful when we can slow the natural aging process of vegetables and fruit. Growers need to manage four natural processes: respiration, transpiration, ethylene production and potential chilling injury. Immediately after harvest root crops such as carrots or beets should be cooled and then stored at their optimum temperature and relative humidity (RH).Other crops such as potato, onion and winter squash benefit from a curing period before being cooled to their ideal storage temperature. Different crops prefer specific types of storage: cold, cool or warm combined with moist or dry conditions.
“Quality cannot be improved after harvest,” noted Stivers, “it can only be maintained. For best storage, start with the highest quality crop from the varieties best suited to your site; control pests all season, manage water and nutrients and harvest at the optimal time.”
Successful storage begins with good harvest practices. “Treat all your crops like eggs,” Hazzard and Stivers agreed. One bad apple really does spoil the whole barrel. Cull cut, bruised and damaged vegetables and fruits before storage. Bruising and cuts cause excess respiration, ethylene production and offer disease a way to get inside skins and rinds. Mechanically damaged fruits and vegetables also lose water more rapidly. Proper curing of skins and rinds can help heal wounds, retain moisture, reduce shrinkage and extend storage life.
Prompt postharvest cooling is critical for most vegetables to lower respiration rates, slow water loss, inhibit potential mold and bacteria growth and reduce ethylene production (ripening agent). Cooling methods include room-cooling, forced-air cooling, hydro-cooling and icing.
While some crops benefit from cold storage, others suffer cold injury and decline quickly in cool conditions. All crops need consistent temperatures. Rising and falling temperatures can encourage condensation and quickly rot a crop. Oxygen and air circulation are critical to allow respiration to keep the crops alive. Be aware of the ethylene produced by fruits like apples, pears, peaches, plums, cantaloupes, tomatoes and several tropical fruits like bananas.
Wash at Harvest or Wash Later:
Many growers prefer to brush off but not wash root crops before placing them in storage. Hazzard said some carrot farmers found staining on carrots unless they washed them before long-term storage. Chlorine or other sanitizing agents in wash water and hydro-cooling water help protect against rot and other storage problems as well as consumers. If you do wash root crops before storage, be sure they are dry when you pack them up.
Potatoes:
Maturity is reached when vines are dry and tuber skins are set. Ideal harvest temperatures should be 45 to 60oF. Cure before long term storage by holding at 50 to 60oF and 95% RH for 10 to14 days. Long term storage temperatures should be 38 to 40o F. Properly harvested and stored potatoes typically last 3 to 6 months or as long as 6 to 9 months. Beware mixing crops in closed storage spaces as exposure to ethylene encourages potatoes to sprout. Temperatures below 45o F cause cold injury darkening potatoes and turning starches to sugars.
Potatoes can cure in storage bins and need good air circulation. Concrete floors are OK for potato storage areas. Potatoes do generate some heat on their own so can be stored in insulated areas without much supplemental heat in cold climates.
Winter Squashes and Sweet Potatoes:
These crops benefit from warm, dry storage at or near 55o F. Squash are mature 45 to 50 days from bud set and can be harvested any time thereafter. Winter Squash maturity is indicated by rind hardness, color and corking of stems. Crops should be harvested before frost or cold nights below 50oFand cured for at least a week before storage to allow any bruises or cuts to heal. Curing at 80 to 85oF and 80 to 85% RH for 10 days helps harden rinds, but this not recommended for acorn or green rind squashes. Remove the hard stems on Butternut and other Moschata type squashes to avoid damage to other squash in the same storage bins. Optimum storage temperature: 55 to 59oF or 50 to 55oF for green rind types. RH should be 50 to 70%. Squash are very sensitive to chilling injury when held below 50oF. Root cellars and temperatures below 50o F can cause cold damage. Most squash can be stored 2 to 3 months, longer for Hubbard and butternut squash and shorter for acorn and delicata squashes.
Onions and Garlic:
Maturity is indicated when 10 to 20% of the tops lay down in the field. Undercutting 1 to 2 inches can accelerate dormancy. Field curing is ideal when temperatures are over 75oF. Tops should be removed after at least two weeks of field or bench curing before dry cold storage of alliums. Forced air curing can be as fast as 12 hours at 86 to 105oF. Onions are ready for storage when their neck scales are completely dry and should be stored at, not below, 32oF with 65-70% RH for best scale color. Onions can be stored up to 6 to 9 months; but typically only 3 to 6 months. Ethylene exposure encourages sprouting.
Carrots, Beets, Turnips, Parsnips, Rutabagas and Cabbages:
Harvest these crops cold and keep them cold. Their freezing temperature is 29 to 30o F so a mild frost will not be a problem. These crops need cold, moist storage. Carrots like 95 to 99% humidity and 32oF. Avoid liquid water which can speed rot. Be sure to trim carrot tops to within ½”. The later the harvest can be delayed, the greater the stability in storage. Hazzard notes that Bolero carrots are widely grown for storage in New England; Chantenay and Berlikum have good potential as storage carrots as well.
More mature carrots will store longer than less mature ones. Carrots can typically be stored 3 to 5 months under good conditions. Be sure to store these crops separately from ethylene producing crops like apples; exposure to ethylene can cause bitter flavors.
Some farmers wrap individual cabbages before storage allowing them to store onions in the same rooms. Others wrap bins or pallets with moist burlap. Fans inside coolers keep some air moving through holes in the bottom of the bins. Household misters can help maintain high humidity levels.
Additional postharvest information is available (crop by crop) in the USDA Agriculture Handbook Number 66. Click here for more information and publications. Readers can join the online Winter Grower Discussion Group.
For more information, contact Ruth Hazzard via email, at the Department of Plant, Soil & Insect Sciences, Agricultural Engineering Building, University of Massachusetts, Amherst, MA 01003 or call (413) 545-3696. You can contact Lee Stivers, County Extension Director via email at, through the Penn State Cooperative Extension - Washington County office at 100 West Beau Street, Suite 601, Washington, PA 15301 or call (724) 228-6881.
Summaries of most of the presentations from the 2011 New England Vegetable and Fruit Conference are available here. A summary of Lee Stivers’ talk “Meeting Post-Harvest Needs of Vegetables from Field to Long-term Storage” starts on page 104.
A similar story also ran in the February, 2012 Eastern edition of "Country Folks Grower."
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