Pumpkins and winter squash, such as acorn and butternut, need to be harvested when the rind is hard, mature and is unable to be punctured with a fingernail. If you have been keeping up with timely fungicide sprays to control powdery and downy mildew, the vines will be healthy and shade the maturing fruit, keeping it in a sound condition until they are harvested. If the vines are beginning to break down due to fungus diseases, then the fruit will be exposed to the sun, causing sunscald. Sunscald will bleach the rind and soften it, making it susceptible to secondary fungi which will cause premature breakdown and spoilage. If your vines are breaking down, then harvest needs to be done immediately even if the rinds are not hard and the pumpkins have not developed a deep orange color. As long as they have started to turn color, they will continue to ripen if given the proper conditions.
Immature pumpkins can be ripened and cured in a well-ventilated barn or greenhouse. The best temperatures for ripening are between 80-85 degrees Fahrenheit with a relative humidity of 80-85 percent and with night temperatures in the mid-60s. Do this for about 10 days. If pumpkins are mature, the curing process can improve storage life. As the fruit skin hardens, wounds heal and immature fruit ripens, which prolongs the storage life.
After curing, store pumpkins in a cool, dry place between 50-60 degrees and a relative humidity of 50-70 percent. Higher humidity allows condensation on the fruit with risk of disease and lower humidity can cause dehydration. Higher temperatures increase respiration and can cause weight loss. Temperatures lower than 50 cause chilling injury. In a greenhouse, temperature can be managed with ventilation on sunny days. Unless it is quite cool, heat is not likely to be needed if the house is closed up at night.
Storage life depends on the condition of the crop when it comes in and your ability to provide careful handling and a proper storage environment. All fruit placed in storage should be free of disease, decay, insects and unhealed wounds. When harvesting squash and pumpkins, it is important to handle the fruit with care to avoid bruising or cutting the skin. Despite its tough appearance, squash and pumpkin are easily damaged.
The rind is the fruit’s only source of protection. Once that rind is bruised or punctured, decay organisms will invade and quickly break it down. Place fruit gently in containers and move bins on pallets. Leave the stems on pumpkins and winter squash to avoid disease organisms from entering. However, be sure not to puncture the rind of other fruit with the stems.
Take care to avoid subjecting pumpkins or winter squash to chilling injury. Chilling injury occurs when squash or pumpkin is exposed to temperatures below 50 degrees in the field or in storage. Injury increases as temperature decreases and/or length of chilling time increases. Chilling injury is of particular concern with squash intended for storage because it increases the likelihood of breakdown. Remove pumpkins or squash from the field if temperatures likely to drop below 50 degrees for any length of time.
A period of curing after harvest can help extend storage life of squash. This may be done in windrows in the field — especially with a series of warm, dry days — or by placing squash in a warm dry atmosphere (70-80°) with good air circulation, such as a greenhouse, for up to two weeks. This pre-storage treatment permits rapid drying of the outer cell layers and when combined with a dry atmosphere for storage, inhibits infections that can take place. Any clean cuts during harvest are likely to heal over during curing and will no longer be a source for injury or infection later.
After curing, move squash or pumpkins to a dry, well-ventilated storage area. Pressure bruises can also reduce storage life, so avoid rough handling, tight packing or piling fruit too high. Fruit temperature should be kept as close to the temperature of the air as possible to avoid condensation, which can lead to rot. Ideally, the storage environment should be kept at 55-60 degrees with a relative humidity of 50-70 percent. Lower relative humidity increases water loss, resulting in reduced weight, and if excessive, shriveling of fruit. High relative humidity provides a favorable environment for fungal and bacterial decay organisms.
Under ideal conditions, disease-free pumpkins should have a storage life of eight to 12 weeks and butternut squash up to three or four months. Even if it is difficult to provide the ideal conditions, storage in a shady, dry location with fruit off the ground or the floor is preferable to leaving fruit out in the field.
Some of the above information was adapted from “Pumpkin and Winter Squash Harvest and Storage” from UMass Extension.