Frost Protection in the Vineyard: Environment, Geography and Science

By: Gerald Dlubala 

The grapevines that a grower depends on for their livelihood are vulnerable to temperature changes that can damage the buds, fruit and even the vine. One of the most unfavorable temperature conditions is frost. Most frost conditions are radiation frosts, characterized by dry, cold air masses that settle into an area with the dangerous combination of no noticeable wind or cloud cover with a low dew point. Temperatures can be relatively warm throughout the day, with the ground retaining heat. As the sun sets, the ground warmth radiates to the upper atmosphere, allowing colder air to fall and settle into the pockets of space now available at lower elevations. Proper frost protection measures can help avoid damage and make the difference between a profitable or unprofitable year. 

Shooting The Breeze And Fighting Vineyard Frost 

  “Wind machines play a major role in protecting your vineyard from the elements of frost,” said Dean Hauff, Marketing Manager for H.F. Hauff Company Inc. “It only takes about 20 minutes before frost starts to damage to your vines, and it’s absolutely critical to protect the primordia bloom. It’s the difference between successful and unsuccessful yields. The primary bloom produces the highest quality fruit, and wind machines help protect the high-quality grapes needed to make premium wine.” 

  Hauff told The Grapevine Magazine that his Chinook wind machines work independently without any other means of auxiliary heat about 90% of the time. The only time a wind machine, or any protection strategy, struggles to be effective is in the rare occurrence of an advective freeze condition. An advective freeze happens when large, arctic air masses replace the warm air and are associated with moderate to strong winds, no temperature inversion and low humidity.  

  “Warm air rises, and cold air sinks,” said Hauff. “We all know that, but at some point, the warm air stratifies in the atmosphere, creating an inversion layer that holds in the warmer air. Wind machines work by pulling the warmer, more buoyant air from that inversion layer and mixing it with the colder, denser air on the ground floor. The fan shaft of the Chinook’s top gear head is built with a six-degree angle of attack, enabling the fan to pull the warmer air from higher altitudes, estimated to be approximately 350 feet up into the atmosphere. The movement of air combined with the mixing of the warmer and cooler air raises the temperature three to five degrees Fahrenheit on average, a notable difference.” 

  H.F. Hauff’s Chinook wind machines are useful year-round in vineyards. They help protect the fruit buds in the spring, the leaf structure in fall, allowing for the continuation of Brix development in the grape berry, and they help protect the vine from excessive cold in winter. The first commercial wind machines were sold in 1937. Since then, research and development have continued to improve coverage, serviceability, performance and ease of operation.  

  “They really are a lifetime investment,” said Hauff. “Wind machines are long-lasting, require only minimal service, yet they retain a high resale value if needed. They’ve allowed vineyards to expand their crop production by transforming frost-prone areas of their farms into fully useable crop-producing areas. Using wind machines in the vineyard lessens the burden, anxiety and stress that goes along with the risky business of growing crops. And with tighter profit margins, it’s always important to produce a marketable crop every growing season.” 

  Today, wind machines are more economical and easier to maintain and service than ever before. They’re considered one of the best tools in protection against radiant frost, lessening and sometimes eliminating the need for extra heaters, smudge pots and water. Wind machines work to bring up the overall vineyard temperatures on average three to five degrees Fahrenheit above the critical temperature point, even in winter temperatures of -15 degrees Fahrenheit or less. Critical temperatures vary depending on the varietal and the stage of development of the vine. The more advanced the stage of development, the less the plant tissue will handle below the 32 degrees Fahrenheit mark. 

  “Our Chinook wind machines use propane, diesel, natural gas or electric,” said Hauff. “The propane units burn about 13 gallons of fuel per hour, and the diesel units use about five and a half gallons per hour. One Chinook wind machine effectively covers 15 acres of fruit and trees and up to 18 acres of vines or vine plantings. They can start and stop automatically and can even be controlled and monitored remotely through telemetry via your cell phone, computer or tablet, no matter your location.” 

Wind Where You Need It 

  “As to placement, we map out and locate each of our wind machines individually, either on paper or in person,” said Hauff. “Our goal is to maximize fan coverage in the vineyard without going outside of the specified boundaries. We protect the lowest ground first, as the coldest air will naturally settle there. Then, we account for natural drift and locate our wind machines 40 to 60 feet into the direction of that natural drift. We also feature special models for uniquely contoured or sloping grounds. Our Chinook fan propeller extends coverage an additional 100 to 150-foot radius beyond competing products, and the unique and exclusive trailing edge wedge of our Chinook fan propellers increases the velocity of the air and widens the sector angle of coverage from 47 to 49 degrees out to 80 degrees.” 

  Hauff said that ice nucleation begins to form after four minutes of no air movement under normal radiation frost conditions. Chinook fans start protecting the fruit bud and plant after three and a half minutes. In addition, Chinook’s more comprehensive sector angle coverage mixes air in the horizontal and vertical plane, providing additional plant tissue protection from the ground up in even, uneven or up to four degree sloped areas with no special add-on equipment needed.  

  Hauff also offers a model that raises and lowers to the ground via hydraulic cylinders to eliminate the need for climbing and allow more accessible and safer servicing and maintenance. Annual recommended preventative maintenance consists of changing oil, checking the gearboxes, and greasing the tower and fan. Hauff said that this is usually accomplished in under an hour and requires no specific skill or unique expertise.  

Grapevines In The Mist: Battling Frost With Misting Machines 

  Another method to thwart the harmful effects of frost is through a technique involving misters and targeted directional spray. Resource West, Inc. offers humidification systems to optimize and maximize operations and serve multiple purposes within many industries, including vineyards and wineries. Their thermodynamic humidification systems protect vineyards from adverse weather conditions ranging from extreme heat through frost and freezing temperatures. The units add humidity into the air when needed or provide cooling for crops during extreme heat situations. These humidification systems give vineyard managers better crop control while providing winemakers better aging control over their products. The system can be successfully used indoors in barrel and aging houses and outdoors throughout the vineyard.  

  “Our humidification systems work by 3x convective dilution (thermophoresis), velocity control for droplet trajectory and droplet size control,” said Robert Ballantyne Jr., Senior Vice President, Principal Engineer, and Atomic and Molecular Spectroscopist for Resource West Inc. “Our larger, outdoor systems offer surface tension control for proper wetting of soil or foliage to fit the current environmental conditions and offer protection from frost, damaging cold or extreme heat.” 

  Ballantyne Jr said RWI’s humidification systems get positioned in a vineyard’s higher elevations, allowing the cooling process to cascade down the slopes. “We cover large acreage, but for the best use, a civil engineering plan should be worked out to discover the best placement of the units to realize the greatest effectiveness of the systems. We determine the optimum number of units to locate within your vineyard through thorough questionnaires and detailed weather analysis.” 

  A misting humidification system allows water droplets to freeze and coat any new or green exposed plant tissue, providing a protective coat for that new tissue against frost conditions. Experts recommend providing a steady or continuous stream of droplets for maximum protection when conditions remain below freezing. 

  “In addition to frost protection, our units provide a nice cooling effect from the evaporation that naturally takes place,” said Ballantyne Jr. “Heat relief from our systems protects crops in temperatures ranging up to 120 degrees Fahrenheit. And since the cooling process is physics-based, the success rate is 100%. The decision to do it at that point is usually a cost-benefit decision, based on cost and the amount of acreage covered by the units.” 

Easy To Own, Easy To Use, And Easy To Maintain  

  Ballantyne Jr. said that many clients prefer a rent-to-own option when choosing a humidification unit. RWI always performs the analysis and engineering tasks needed before purchase, but the systems are fully functional and generate benefits on a year-round basis. The number of benefits gained by year-round use varies based on the client’s geographic location.  

  “Maintenance and training are non-factors in choosing our systems for your vineyard,” said Ballantyne Jr. “We recommend that our units get an annual power washing, and the training involves understanding your vineyard’s elevation changes and how cooled air will flow and sink with varying increases in density. With RWI’s systems, you gain a partner in crop protection and enhanced product quality. If you are a client, we work with you to continuously improve performance and maximize your return on investment. We are proud to offer the most efficient systems on the market, and our engineering staff is always available to help ensure the highest return for our clients.” 

  Inside the winery, where humidity is also critical, RWI’s humidification systems aid in controlling the barrel aging process, giving winemakers better control of the quality of their final product. Benefits of increased control are more effective management of angel share losses, improved barrel loss conditions, and enhanced quality and consistency of wine, ultimately leading to better financial performance. 

Like a Warm Hug: Wrapping Vines as Protection from Cold  

  Can something as simple as wrapping your vines in a cover protect them from frost? Two estates in the Anjou-Saumur region of France have participated in frost protection trials, using a common backyard tactic for protecting tender vegetation. Monitored by the National Institute for origin and quality, grapevines were wrapped in a P30 type winter cover to determine if it protected the vines in frost conditions. Complete frost protection was reported in the 2020 growing season. In 2021, Mother Nature provided even more opportunities to test the process as recorded temperatures dropped below freezing several times over four weeks. Again, the results were very positive, as the wraps reduced frost damage significantly. Unprotected vines suffered nearly a 90% loss, whereas protected vines experienced only a 10% loss. Another grower used a double layer of fleece as their wrap of choice and again showed success, recording up to a four-degree difference in the covered vs. uncovered areas.  

  However, the Institute warns that although it looks promising, more research is needed to understand the full scope of how wrapping affects the grapevines, not only externally but also within the vines’ structure, before they issue a recommendation on the future viability for this type of protection on a widespread basis. 

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