Washington fruit growers know Mother Nature can take out a fruit crop overnight

Learn why low temperatures are a threat to blossoms and what growers must do to save their crops. It's hard work and it can be emotional for growers whose livelihood depends on protection from the cold.  Be sure to scroll to the bottom to read a firsthand account of one very cold night in the orchard.

Frost can damage any fruit crop. As air gets colder it not only sinks, but it becomes dry and can begin to flow like a liquid into low areas. Sometimes this mass of cold air creates frost pockets where very low temperatures can damage tender blossoms. By using tall fans to pull down some of the warm air above or just push the cold stagnant air out of the orchards, growers can prevent frost damage to blossoms.

Wind machines tower 40 feet over orchard below

Click below to hear a grower explain how he protects his fruit blossoms

The temperature at which fruit buds are injured depends primarily on their stage of development. Buds are most hardy during the winter when they are fully dormant. As they begin to swell and expand into blossoms, they become less resistant to freeze injury. Brown petals, like those pictured above, are a sign of frost damage.

Irrigation-ice can save blossoms

Depending on the type of fruit, growers can judiciously apply water to an orchard threatened by low temperatures. Heat is released as water changes to ice, which keeps the orchards warmer than freezing. If supplied at an adequate rate, the water will keep the temperature of the plant at or near 32° F, which prevents frost damage. Another means of protection is to coat the blooms in ice to protect them from very low temperatures.

Photo courtesy WTNH news, April 6, 2016

Read one Washington grower's frost season story

"My responsibility as a grower is to make sure my crop makes enough money to sustain a viable business which benefits people all over the world with healthy, fresh and affordable food."

by Phil Madden, PM Orchards, Manson, WA

     Early in my career, I managed a 256-acre cherry orchard near Chelan, Washington. The owner was in a very precarious financial position. All hopes for his future hung on this one crop we were about to produce.

     In the last week of April, the cherry bloom had just begun to emerge from a massive amount of swollen buds on each of thousands of trees. At 5:30 pm one night I got a call from the owner, his voice tight with tension. “Phil, there has been a sudden change in the weather forecast. There is an arctic air mass approaching us from Canada. We must get ready for temperatures to drop to 22 degrees tonight.” I quickly checked the chart from WSU that shows how much cold cherry blossoms can tolerate at various stages of blooming. Our blossoms were in stage 5, called ‘first white’, the most sensitive bud stage to frost damage. 10% would be killed at 26 degrees and 90% would be killed at 22 degrees. We might lose the entire crop tonight.

     At 7:00 pm I switched on the local radio and listened to the Fruit Frost Forecast. I listened carefully as region by region, the minimum temperatures were reported and the time they were expected to arrive was forecast. Finally, I heard the Chelan report. The drop to the minimum of 22 degrees could begin at 10 pm in the coldest areas. Wow! It was going to be a long night. The report continued: the weather front was likely to be very cold at onset but a few clouds and a slight chance of precipitation would be coming in about 2 am. We had to get to work if we wanted to save the crop. 

     I rounded up a couple of crew members who, after putting in a full day in the orchard, were willing to stay up all night till temperatures were back above 32 degrees. We would need to turn on our under-tree irrigation system and start the twelve propane-fueled wind machines. The wind machines were strategically placed in frost pockets where cold air settles in pools. Each one with its powerful 14-foot blades, could break up the air in approximately 10 acres of orchard.

     Just before 10 pm we set out in pick-up trucks and 4-wheelers. We needed to get the fans ready to go and get the irrigation risers and nozzles flowing before ice could develop. Water uses energy to freeze and just by keeping moisture in the air and on the ground, temperatures can be prevented from dropping below freezing. Water freezing on buds will also protect them in a jacket of ice that keeps them at a survivable 32 degrees. We traveled quickly down the rows of trees, assessing the danger by checking each temperature-recording thermometer placed along the roads.

     By 11 pm the temperature had dropped to 28 degrees and continued to drop faster as the night progressed. At one moment, I gazed up at the brilliant stars. They were so clear and bright I felt I could see the depth of light-years between them. A deep chill penetrated to my bones. We needed to save fuel and costs, so we waited till the last minute to start up the wind machines. The temperatures were now reaching the critical minimum. Hopefully we were not too late and we would not run out of fuel before the temperatures rose to safe levels the next morning.

     At first, we were able to slow the temperature drop with our water and wind machines. Some areas even briefly improved to 30 degrees. But soon the temperatures were dropping again. It appeared we were losing the battle with Mother Nature. By midnight we were recording temperatures of 24 degrees. I gazed vacantly at the huge, powerful blades, lit by flood lights and rotating 40 feet above me. Their efforts were easily matched by the forces of nature.

     Suddenly, about 2 am, I noticed a feel of moisture in the air. I looked up and saw the stars disappearing. My feelings of helplessness began to relax as I realized the predicted cloud cover was finally arriving. The clouds would act like a natural blanket to protect the trees from the cold of the clear night sky. In some areas of the orchard, temperatures had reached 22 degrees. But they were stabilizing now. We took a warm-up break in a pick-up truck. While sitting quietly in the cold, the smell of moisture suddenly became intense. Huge, golf-ball sized snowflakes started to fall like a blanket of over-sized confetti. The large snowflakes, illuminated by the flood lights, revealed an unforgettable sight. As snowflakes encountered the blast from the wind machines they appeared to explode into sparkling dust as they were briskly blown out of sight into the darkness.

     The snow gently covered the trees and blossoms. Temperatures rose to 30 degrees for the remainder of the night. At sunrise, the temperatures jumped above freezing and we shut down the wind and water. We were tired, but elated that we had made it through the night. We all shared feelings of accomplishment and victory as we took in the beauty of 2 inches of snow shining under the gorgeous sunrise.

     Then we were sobered with the reality that this was frost season. The snow would quickly melt in the sun. In 12 hours, we would most likely have to be ready to do it all again.

photos by Phil Madden