Frosty reception

Frost hits when the new growth is at its most vulnerable.

One of the key impacts of climate change globally is the increase in extreme weather events. These are classed as weather which is unusually violent or abnormal in its duration or frequency. While a trend towards milder winters, and an overall warming in our geographical zone, is noted, the risk of spring frosts has not decreased or altered. This puts vines at particular risk due to earlier budbreak. The frost hits when the new growth is at its most vulnerable.

The devastation that frost can wreak on the newly awakened grapevines has led to renewed interest in finding innovative solutions for minimisng or preventing the damage, which may be used alongside more traditional methods like heaters and sprinklers. Measures taken to mitigate frost are traditionally divided into three categories; active, passive and chemical.

Types of frost

Radiation frost

When the nights are clear and calm, radiation frost is the enemy. As the sky is colder, the ground’s warmth is transferred upwards. Very cold air settles close to the ground, particularly in any shallows where it can pool. The warmer inversion layer above is utilised by a number of frost protection techniques to mitigate against damage.

Humidity can offer a degree of protection from radiation frost damage. High levels of humidity in the air causes white frost on the vines. Temperatures remain close to zero and although the vine is covered in a white coat or even ice, this may actually protect the buds. Soil moisture can also help to absorb and store heat during the day, reducing the risks at night. 

Advection frost

On cloudy, windy nights, advection frost can strike. A large mass of cold air, with a temperature of below 0°C is brought in by strong winds and surrounds the vines. The temperature may dip well below 0°C and stay there long into daylight hours.

Active frost protection measures rarely guard against this type of frost because of the strong winds and lack of a readily available source of warmer air.

Evaporation frost

This type of frost is caused by the loss of water through evaporation from the surface of a plant. It happens when relative humidity drops and dew evaporates. The transfer of energy used to evaporate the water requires heat – which ultimately cools the plant.

Evaporation frosts are classified as types, thanks to their visual appearance. There are white frosts which form on plants. It usually occurs when there is high humidity, low wind and clear, cold skies. A black frost sees no ice formation. The black name refers to the appearance of the plant material it destroys. This type of frost comes when the air is drier, and overcast skies are more likely to see the formation of black frost.

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Frost forecasting and management

Early in 2024, Innovate UK announced that a project with “the potential to revolutionise frost-related crop protection” had secured £300,000 funding from themselves and the Department for Environment Food and Rural Affairs.

The Smarter Forecasting, Communication and Management of Frost Risk in Vineyards project seeks to create site specific, hyper localised frost risk forecasts which are tailored to different varieties of grapes. The project is being led by sensor manufacturer Terraprima and agri-tech facilitator Agri-Epi Centre, and supported by land-based education provider Plumpton College, vineyard and winery consultancy Vinescapes, vineyard monitoring solution Vinewatch, weather forecasting provider WeatherQuest, and WineGB.

The two year project started with sensors being installed at Dillions Vineyard in West Sussex, JoJo’s Vineyard in Oxfordshire, Tanhurst Estate Vineyard in Surrey, and Plumpton College, Quarry Wood and Ridgeview in East Sussex. The sensors were used to “assess frost risk at a micro level.” Weather forecasting models were combined with mapped frost risk assessments and real-time measurements from the vineyards to give site-specific forecasts for both frost risk and type. Ultimately, it is hoped that these models will be able to provide frost alerts direct to mobile phones via an app.

Speaking about the project, Eliot Dixon, Head of Agri-Tech Engineering at Agri-Epi Centre was optimistic about the potential of the research: “Through this project, we will be providing a vital early warning of frost risk to vineyard managers, at a precision never achieved previously. This uses a fusion of weather modelling, IoT sensors and remote sensing to create a robust and commercially relevant solution that shows the very best of UK agri-tech.”

Vineyard Magazine looks forward to hearing more ongoing detail about the project in due course.

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Frost mitigation measures

Air heaters

Frost candles, smudge pots or bougies have been used to protect vineyards for generations now. They are an effective method of helping to keep the temperature in the vineyard up during a frost event. The aim is to heat the air as uniformly as possible up to the inversion layer.

The number of candles that need to be placed will be dependent on the size and spacing of the vineyard in question.

The downside is that bougies are labour intensive to install during adverse weather and have a relatively significant environmental impact, since they can be burning fuel for several hours a night.

Companies like Stopgel have been working hard to create products that are more sustainable. Their anti frost candles burn natural biofuel and have a low smoke emission.

Find out more about the Stopgel range:  www.stopgel.fr

Mechanical heaters can also be used to raise the temperature of the vineyard and prevent frost from settling. The AgroFrost FrostBuster uses phase transition to control the formation of ice and make use of the energy that is liberated when vapour changes into ice. This can reduce the amount of energy required to protect a vineyard. This method is effective during both radiation and advection frosts.

Find out more about the FrostBuster: www.npseymour.co.uk/products/frostbuster

Electrical heating cables

Using an energy efficient system of cables to protect vines against frost damage is considered to be a relatively economical and environmentally sustainable method of mitigating against frost damage. The cables are fed along the trellis wire and the heat they need to emit is calculated against the weather conditions, including wind velocity, the capabilities of the hardware and, of course, safety considerations.

Electric cables do not make any direct emissions, unlike active protection methods like candles, for example. They also have a low energy consumption during their periods of use during frost events. As they are attached to a thermostat, they can operate automatically when needed, although an alarm system is useful to check the integrity of the cables in real time.

Danfoss offers a portfolio of products for businesses looking at installing an electric heating system. The installation consists of the heating element – either a heating cable with a constant wattage or a self-limiting heating cable, a controller with temperature and moisture sensors to automate the system and the various fixing elements needed to position the cables along the row. They can also give advice on understanding what specifications are required to accommodate the geographical location of the vineyard and the expected temperature fluctuations. 

Find out more about Danfoss:  www.danfoss.com

Hydrophobic particle film and acrylic polymers

Covering the plants helps to concentrate any daytime heat near the ground and is therefore the simplest method of frost protection – although the size of a vineyard may render it logistically undesirable. Research has taken place into the efficacy of using a film of hydrophobic particles or acrylic polymer as a cover. In this research, the hydrophobic particles were found to most effectively reduce frost damage, although covering is only seen to give good results where temperatures do not fall below – 3°C.

Late winter pruning

Since dormant buds are protected by their shells, they are more resistant to frost damage than the delicate plant tissue of newly growing shoots. Delaying bud development is therefore another strategy available to the vineyard manager to give the buds the best chance of survival in the spring. There are two techniques for pruning the vines to help achieve this:

• Double pruning – cut back the shoots to 30-45cm above the spur in winter, which could be done mechanically, then wait until as late as possible to do final spur and bud selection.
• Sacrificial canes – Since the buds furthest from the crown will bud first, leaving longer spurs until after the risk of frost has passed can help to keep enough healthy buds to produce a reasonable crop.

A word of warning though, in cool climate regions studies suggest that delaying budbreak can have a negative impact on wine quality because of the knock on delay to fruit development and maturation. 

Oil application

Vegetable oils can be applied directly to the vines to delay budbreak. These products are referred to as “dormant oils” since that is when they must be applied to the plant. They are sprayed on when a severe weather event is expected, and give an additional degree of frost tolerance. Oils will need to be reapplied since the shoots will outgrow the initial spraying quite quickly.

It is worth testing this method on a small area of the vineyard first to assess the impact of the oil not just in its effectiveness at delaying budbreak for those varieties but also any secondary effects on the resulting quality of the fruit.

Selective extraction

Wind machines are usually considered to be an effective protection against radiation frost. They direct warmer air from above towards the vines as well as displacing colder air on the ground. Inverted sink fans can also be used in vineyards that have low-lying areas where the cold air pools. The fan is mounted horizontally and blows the air straight up to a height of about 90 metres. Since it removes the lowest air, it therefore removes the coldest air from the vineyard.

Sprinklers

Aspersion is considered to be one of the most effective methods of protecting vines from frost because it does not rely on the availability of warm air above the vineyard. The plants are continuously sprayed with water above the canopy. As it turns to ice, the freezing process releases latent heat that creates a warming microclimate and helps to protect the plants. A thin layer of ice continually forms and melts on the plants themselves and the energy released by it is sufficient to prevent the plant cells themselves from freezing.

Sprinklers are relatively energy efficient compared to heaters and can work effectively across a large area in both radiation and advection frosts. Plantex offers a range of solutions that work in different ways. For example, Pulsar™ Sprinklers deliver several pulses of water each minute, which gives continuous and uniform watering over a large area throughout the weather event. Alternatively, the Flipper sprinkler spreads water across a long and narrow strip. This means it targets the vine rows specifically, reducing the amount of water and energy needed to operate it effectively. 

Find out more about Plantex:  www.plantexuk.com

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Climate smart viticulture

The effect that climate change is having on growing conditions has made the exploration of “climate smart viticulture” into a key research trend worldwide. 

More and more work is being done on microclimate zoning of vineyards in order to better manage vineyards and defend against extreme weather in a more sustainable way.

Understanding the topographical features like elevation, slope and aspect at the micro level within a vineyard space allows vineyard managers to create a more effective plan for the frost control measures they implement in the early spring. Sensor technologies and drones can be employed to provide valuable real-time data into local environmental conditions, but these sensors can have a high cost to implement.

Detailed work is being undertaken in the UK to better understand the risks and opportunities that climate change presents to the local wine sector. The Grantham Research Institute on Climate Change and the Environment has presented a policy brief that gives a detailed analysis that supports the proactive response to climate change. 

This policy brief emphasises the limitations that the English Quality Sparkling Wine PDO puts on producers who may need to source grapes from other counties as a risk-mitigation strategy when frost damage strikes their land. The report’s recommendations highlight the need for long term decision making that allows flexibility to create a sustainable industry in the long term.

While many wine estates have taken measures to be climate smart, these actions are not always measurable. Denbies Wine Estate in the Surrey Hills National Landscape broke the mould in this regard by being named as the UK’s first Net Zero vineyard in Spring 2024. They worked with the Environmental Asset Management company Beyond Zero to measure their baselines and develop a plan to reach their target.

Denbies had already been actively reducing carbon emissions from the winery and vineyard, but they were able to harness the UK Carbon Code of Conduct framework to measure and verify the emissions that came from their wine production. They were also able to create base maps of the Estate’s so-called “natural capital” – a comprehensive breakdown of the above ground biomass and soil types of the property which allowed the carbon capture potential to be recorded. This meant that as well as continuing to reduce emissions even further, they were able to institute land management changes which would boost the sequestration of carbon through the vineyard soils and habitats.

The upshot was that the 2023 figures demonstrated that Denbies had sequestered more carbon than it had emitted – to the tune of minus 96 tonnes of CO₂e. That’s a reduction equivalent to the annual average carbon footprint of 7.5 people in the UK.

Read more about the UK Carbon Code of Conduct : www.ukcarboncode.org

Read more analysis of the impacts of climate change on UK viticulture on the LSE website:  www.lse.ac.uk/granthaminstitute/wp-content/uploads/2024/04/Adapting-to-climate-change-risk-and-opportunity-in-the-UK-wine-sector.pdf

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Harnessing nature’s latent heat

The science behind Frosco’s foam.

Frosco’s frost protection innovation – a low-cost, plant-based aqueous foam – has sparked a lot of curiosity, with many asking the same question: how does it work?

At its core, the system intensifies a natural process by maximising the release of latent heat as water transitions from liquid to solid.

While modern sprinkler systems already use this principle for protection against frost, Frosco’s system harnesses it far more efficiently.

Unlike sprinkler systems which run all night, the foam is just applied once – minimising water usage and driving down costs.

The release of latent heat drives many processes observed in the natural world. During dew formation, water vapour condenses into liquid droplets, releasing latent heat that can create a thin layer of protective warmth on surfaces.

Frosco’s foam mirrors this natural elegance. By drawing inspiration from these natural mechanisms it offers a solution that is effective and intuitive, a testament to utilising nature’s principles for innovative applications.

The latent heat effect in action

The key to the performance of Frosco’s foam lies in enhancing this latent heat phenomenon through its patented formulation – which consists of entirely plant-based and environmentally friendly ingredients.

So far the foam has produced consistently remarkable results during internal testing. Buds can be protected for several hours at temperatures down to -20°C.

 In addition, independent lab tests simulating realistic conditions have demonstrated complete protection against external temperatures that drop to -4°C.

The results from the independent lab tests are set to be published ahead of Spring 2025.

The foam holds buds at 0°C, which is no coincidence. It is at this point that water transitions between its liquid and solid state, and is therefore when the latent heat phenomenon kicks in.

What is next for Frosco?

Our current focus is on finalising the application of the foam. From handheld solutions to field-scale systems, we are exploring a variety of technologies to ensure the foam can be deployed efficiently across a range of scenarios.

One of the latest developments is a knapsack sprayer. We are making excellent progress in designing a specialised nozzle that can produce high-quality foam.

This is a key step towards enabling individuals and small teams to harness the power of the foam on smaller scales.

Simultaneously, we are developing field-scale solutions that can integrate seamlessly into current vineyard operations. 

By adapting existing industrial spray systems, we aim to enable the rapid and efficient application of foam on a large scale – requiring only an individual or a small team to operate.

Our goal is to ensure a smooth transition for those who already rely on such systems, allowing them to adopt the foam with minimal disruption. 

In December, we tested one such system in Herefordshire, and we will share further updates in next month’s edition of Vineyard Magazine.

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