Seaweed and Kelps for Frost Resilience

Foliar kelp sprays are increasingly discussed as a possible tool for reducing frost injury in vineyards. The attraction is obvious: they are relatively inexpensive, easy to apply, and seaweed extracts contain a complex mixture of compounds that may influence plant water relations, osmotic adjustment, antioxidant activity and stress-response pathways.

But there is an important distinction between improving cold hardiness and protecting a vineyard from a severe radiation frost. The research suggests that kelp extracts may improve a vine’s ability to tolerate freezing temperatures, but they should not be considered a replacement for proven frost-protection systems such as wind machines, sprinklers, heaters or site-based frost management.

How could kelp help a vine tolerate frost?

Frost injury occurs when temperatures fall below the freezing tolerance of plant tissues. Ice formation outside cells draws water from the cells, while intracellular freezing can cause catastrophic membrane damage.

Seaweed extracts may influence several of the physiological processes involved in this stress.

Research on Ascophyllum nodosum has identified effects associated with osmotic adjustment, membrane stability and antioxidant responses. Rayirath et al. (2009), for example, found that lipophilic components of A. nodosum extracts increased freezing tolerance in Arabidopsis thaliana. The authors concluded that the extract influenced physiological and molecular responses associated with freezing tolerance.

This is important because the proposed mechanism is not simply that kelp forms an insulating coating over the leaf or bud. Rather, the plant appears to respond physiologically to components within the extract.

A review published in 2024 similarly concluded that seaweed extracts can influence antioxidant systems, phenylpropanoid metabolism and phytohormone-related pathways involved in plant responses to abiotic stress. However, the authors also emphasised that the precise mechanisms remain incompletely understood.

There is some grapevine-specific evidence

The most interesting evidence for viticulturists comes from grapevines themselves.

Research cited in Australian viticultural literature by Wilson (2001) found that an Ascophyllum-based seaweed extract could alter the freezing characteristics of grapevine tissues. A subsequent review of the research reported that vines treated with a 0.8% Ascophyllum extract showed a reduction in leaf osmotic potential after nine days of treatment.

More recent Australian research has also acknowledged the earlier finding, reporting that Wilson’s work found seaweed extract reduced the critical freezing point of grapevine shoot cells.

This provides a plausible physiological basis for using kelp as part of a pre-frost hardening strategy.

However, there is an important caveat.

The Australian frost-management literature has questioned whether these physiological changes translate into meaningful protection under real vineyard conditions. A review by Lamb (2009) noted that the reported gain from spray-on frost protectants may be less than about 2°C and that field effectiveness had not been scientifically demonstrated.

That distinction is critical.

Timing is likely to be more important than simply spraying on the night of the frost

If seaweed extract is being used to improve cold tolerance, the evidence suggests it should be considered a pre-conditioning treatment, rather than a product applied immediately before temperatures fall.

The grapevine work reported improved freezing tolerance following approximately nine days of treatment, while research in winter barley found that repeated seaweed applications produced substantially greater improvements in frost resistance than a single application.

The barley research is particularly interesting.

Burchett, Fuller and Jellings found that a single seaweed application produced only a small improvement in frost resistance, whereas three applications increased frost resistance by approximately 16% in non-acclimated plants and 7.5% in cold-acclimated plants. Importantly, rainfall after application reduced the persistence of the effect.

Although barley is obviously not grapevine, the study demonstrates an important principle:

If seaweed extracts work as frost biostimulants, the response is likely to involve plant physiological conditioning rather than an instantaneous protective film.

What about the chemistry of kelp?

Not all kelp products should automatically be regarded as equivalent.

Commercial seaweed extracts can differ considerably depending on:

• species of seaweed

• extraction method

• concentration

• processing temperature

• carbohydrate composition

• hormone-like compounds

• mineral content

• phenolic compounds

• application rate.

Ascophyllum nodosum has received considerable attention in the scientific literature, but other species are also used commercially.

The 2024 review of foliar seaweed applications highlighted polysaccharides, pigments, phenolic compounds, proteins, phytohormones and macro- and micronutrients as possible contributors to biostimulant activity.

This means that simply comparing products by the words “kelp” or “seaweed extract” on the label can be misleading.

More recent research strengthens the biological argument

Research published in 2026 has provided additional evidence that seaweed biostimulants can influence freezing stress responses.

A study in Scientific Reports investigated seaweed extract treatments on Valencia orange plants exposed to freezing stress. The researchers found that freezing caused oxidative damage and reductions in photosynthetic performance, while seaweed treatments—particularly combined foliar and root-zone treatment—improved physiological performance under freezing conditions.

Again, this is citrus rather than grapevine, so it should not be interpreted as proof that a kelp spray will protect a vineyard. It does, however, add support to the broader physiological hypothesis that seaweed extracts can influence plant responses to freezing stress.

Other work on tomato has found that brown-seaweed extract improved photosynthesis and yield under cold stress and altered expression of genes associated with cold-response pathways.

So should grape growers spray kelp before frost?

There is enough evidence to justify trialling the approach, particularly where frost is a recurring problem and the grower already uses seaweed as a biostimulant.

But I would not describe kelp as a “frost spray” in the same sense as an overhead sprinkler system or frost heater.

A better description is:

Kelp may help increase the physiological cold tolerance of the vine before a frost event.

That is a much more defensible interpretation of the research.

For a vineyard with a history of spring frost, a sensible trial would be to establish treated and untreated vines or rows and monitor:

• minimum air temperature

• bud temperature if possible

• duration below 0°C

• minimum temperature reached

• budburst stage

• percentage of primary buds damaged

• secondary bud survival

• shoot survival

• subsequent shoot growth.

Ideally, the trial should be repeated across several frost events and seasons.

Don’t confuse frost hardening with frost avoidance

This is probably the most important point for growers.

If the vineyard reaches −5°C, a kelp treatment does not mean the vines are suddenly protected to −5°C.

The treatment may shift physiological tolerance to some degree, but frost injury depends on many factors, including:

• cultivar

• phenological stage

• prior cold acclimation

• bud position

• shoot position

• tissue water status

• duration of freezing

• rate of cooling

• humidity

• wind

• topography

• soil heat release

• whether the frost is radiative or advective.

Consequently, kelp should be considered one component of an integrated frost strategy, not a stand-alone frost-management technology.

Where I think kelp has the greatest potential

The most logical application is before the period of highest frost risk, particularly when vines are approaching or entering the sensitive early-growth stages.

Rather than waiting until the weather forecast predicts −2°C overnight, the strategy would be to use the product beforehand to potentially improve physiological preparedness.

That approach is consistent with the research showing that responses develop over days rather than hours. The barley research also suggests that repeated applications may produce a greater response than a single treatment.

However, growers should follow the registered product label for concentration, application timing and permitted claims, because research concentrations cannot automatically be converted into commercial recommendations.

The bottom line

There is a legitimate scientific basis behind the idea of using foliar kelp extracts to improve plant tolerance to cold and freezing stress.

Research has demonstrated:

• improved freezing tolerance in Arabidopsis following Ascophyllum nodosum extract treatment;

• increased frost resistance following repeated seaweed applications in winter barley;

• changes in osmotic potential and freezing characteristics in grapevine material;

• physiological and molecular responses to cold stress following brown-seaweed applications;

• and more recent evidence of improved physiological performance under freezing stress in citrus.

  
  

But the evidence for actual commercial frost protection in vineyards remains much weaker than the marketing claims sometimes suggest.

For viticulturists, the most appropriate way to view foliar kelp is therefore as a potential cold-hardening biostimulant, rather than a guarantee against frost.

If the vineyard is in a frost-prone region, kelp could be incorporated into the pre-frost management program—but it should sit alongside, rather than replace, proven frost-protection measures.

The practical takeaway for growers: don’t think of kelp as something that “stops frost”. Think of it as potentially raising the vine’s physiological preparedness for cold stress. That is a much more scientifically defensible—and potentially useful—way of approaching foliar seaweed applications in frost-prone vineyards.

Published research and further reading

• Rayirath et al. (2009) – Lipophilic components of the brown seaweed, Ascophyllum nodosum, enhance freezing tolerance in Arabidopsis thaliana. Physiologia Plantarum.

  
  

  PubMed – published research⁠

• Burchett, Fuller & Jellings (1998) – Application of seaweed extract improves winter hardiness of winter barley cv Igri.

  
  

  University of Plymouth research record⁠

• Wilson (2001) – Frost Management in Cool Climate Vineyards. University of Tasmania/GWRDC.

  
  

  This is particularly relevant to Australian grape growers and discusses spray-on frost protectants and seaweed extracts.

• Lamb (2009) – Electrically heated cables protect vines from frost damage at early flowering. Australian Journal of Grape and Wine Research.

  
  

  Useful discussion of the limitations of spray-on frost protectants in vineyards.

• Hort Innovation / Australian research – Effect of seaweed extract application on wine grape yield in Australia. Journal of Applied Phycology.

  
  

  This provides useful Australian field evidence on seaweed extracts in wine grapes and discusses the earlier frost research.

  
  

• Ali et al. (2021) – Biostimulant Properties of Seaweed Extracts in Plants: Implications towards Sustainable Crop Production. Plants.

  
  

  Full-text research review⁠

• 2024 review – Potential of Foliar Application of Seaweed Extracts as a Biostimulant for Abiotic Stress Alleviation on Crop Production.

  
  

  Full-text review⁠

• 2026 – Seaweed biostimulant enhances freezing tolerance in citrus via coordinated redox regulation and metabolic adjustment. Scientific Reports.