Spring 2025 has been a direct contrast to Spring 2024, with unseasonally low rainfall throughout February, March and April.
According to the BBC weather department, Sheffield’s Weston Park weather station has recorded just 78mm (3in) of rain since the start of February, which is 50% of what would ‘normally’ been seen and only a drop compared to the 300mm (11.8in) seen in the same period last year.
Coupled with low rainfall we have had higher than average daytime temperatures with the end of April confirming it as the hottest April for seven years and the beginning of May breaking daytime temperature records again.
It may seem that farmers and growers are never happy with the weather as they wish for weather normality to be restored (slightly more rain and a little less heat), but this is because both heat and drought are extremely detrimental to yield and quality of all crops, and potatoes are particularly at risk.
Potatoes are a cool climate crop, which require constant moisture to maintain growth and especially during tuber initiation and bulking, the critical times for yield establishment.
Potatoes are sensitive to temperatures above 20°C, which can start to impair photosynthesis, delay tuberization, and reduce yield. This becomes acute above 25°C. Drought stress exacerbates these issues by limiting water availability, leading to reduced plant growth and tuber development.
Combined heat and drought stress can have a more severe impact than either stress alone, affecting both the physiological and biochemical processes in the plant.
Why are heat and drought detrimental to potato crops?
Potato crops are particularly vulnerable to each stress individually but face a double whammy when hit with both at the same time, and this is a challenge because:
- A lack of water reduces root uptake, which in turn reduces the delivery of vital nutrients and other important molecules to the cells. Water-stressed potato crops can show reduced or stunted growth, low flower numbers and small tubers. These crops are also more vulnerable to disease and pest attacks.
- Excessive heat damages leaves, and over a sustained period causes senescence or ‘brown out’ and finally shedding. In sustained periods of high heat, photosynthesis is reduced and the plant focuses on survival, which results in it using its own carbohydrate reserves to try and survive. In potatoes, tuber bulking is halted, as the plant goes into survival mode – a disaster for crop yield.
Chart 1. Issues caused by heat and drought stress
| Feature | Heat Stress | Drought Stress |
| Main Trigger | High temperatures (>22-25°C) | Inadequate soil moisture |
| Critical Growth Stage | Tuber initiation and bulking | Tuber initiation and bulking |
| Yield Impact | Fewer, smaller tubers | Fewer, smaller tubers |
| Tuber Quality Issues | Misshapen, poor skin finish, sugar accumulation | Misshapen, hollow heart, cracking |
| Plant Physiology Impact | Reduced tuberization, photosynthesis declines | Reduced photosynthesis, early senescence |
| Canopy Effects | Leaf scorching, poor canopy development | Wilting, yellowing, early dieback |
| Nutrient Uptake | Impaired by root damage and stress | Impaired due to low moisture movement |
| Disease Susceptibility | Increased (e.g. blight, bacterial wilt) | Increased (e.g. dry rot, black scurf in cracked tubers) |
| Recovery Potential | Limited if prolonged or during key stages | Some recovery if irrigation is restored early |
While the obvious remedy to drought stress in potatoes is to irrigate, this is becoming more problematic as reservoir levels are low from the dry Spring with many areas facing the prospect of water restrictions before we reach the height of summer. In any case, many growers do not have access to irrigation for part or even all of their crop.
Combating the effects of heat and drought stress in potatoes
Over twenty years of nutritional and biostimulant trials have repeatedly demonstrated that crops supported throughout the growing season in this way are able to continue with normal growth for longer while withstanding prolonged heat and/or dry conditions better.
Combinations of organic and inorganic bioactive molecules can stimulate plant growth and fruiting productivity by supporting the crop in the following ways:
Improve root development
Biostimulants based on seaweed extracts, humic acids and beneficial microbes stimulate root growth; the better the root system the more soil water they can locate during dry spells.
Enhancing water use efficiency
Certain biostimulants can improve stomatal regulation, thereby reducing water loss through transpiration and assisting the plant in retaining more moisture within its system during periods of high temperatures. When soil moisture availability is low, reducing water losses helps to maintain the crops internal equilibrium.
Improved nutrient uptake
During times of heat and drought stress, nutrient uptake can become inefficient and limited; biostimulants improve nutrient solubility and transportation around the plant. Ensuring that the plants receive the nutrients it needs to continue to function i.e. flower, tuber set and bulk during a time of environmental stress.
Stress responsive enzymes and antioxidants
During periods of stress, plants can suffer from a build-up of reactive oxygen species (ROS), which are highly reactive molecules containing oxygen that can damage cells by oxidizing proteins, lipids and DNA within the cells. Biostimulants that boost the production of antioxidants and enzymes that neutralise the build up of ROS are critical to maintaining plant health.
Osmotic regulation
The amino acid and protein hydrolysates within biostimulants support improved osmotic balance within cells, allowing potatoes to retain more water and maintain turgor pressure during times of water scarcity.
Hormonal balance
A number of biostimulants contain active plant hormones, polyphenols and polysaccharides that can, together, act to assist in the closure of stomata, reducing water loss, or promote cell repair and growth even under stressful situations.
Incorporating biostimulants designed to reduce drought and heat stresses into potato cultivation practices can enhance resilience to heat and drought stress. Regular applications during critical growth stages, through tuber initiation and into bulking, are recommended to maximise benefits. Selecting appropriate biostimulant products and application timings based on specific environmental conditions can further optimize outcomes.
Biostimulants provide the commercial potato grower with the ability to deliver support to their crop nutrition programmes before and during periods of limited rainfall and/or high temperatures. By helping to maintain yields and quality in the face of challenging weather patterns, they are able to achieve better productivity, maximise nutrient use efficiency and thus take advantage of any increase in prices caused by crop shortages elsewhere in the market.
Foliar Nutrition
Finally, foliar nutrition applied during periods of drought bypasses the root system and directly supplies the crop with needed macro and micro nutrients, especially major nutrients like nitrogen, phosphorus, potassium and magnesium.
In combination, the right biostimulants and foliar nutrients, applied in the right amounts at the right time will allow the crop to survive better and continue to produce productive and useful yields.
Biostimulants that support crops in dry weather
BioBoost –https://bit.ly/3yRCGLv
BioZest – https://bit.ly/3YobgLm
Activator organic acids and biostimulants – https://bit.ly/4861dgV
Diamond Foliar biostimulant- https://bit.ly/3Q4EUQW
SeaSpray 100% cold pressed natural seaweed extract – https://bit.ly/3RyIG5X
Foliar nutrition that supports crops in dry weather
Folia-N foliar nitrogen – https://bit.ly/4c3EVgu
Superphos folair phosphate – https://bit.ly/3wgbF7f
OptiPot foliar potassium – https://bit.ly/3RQ4Kce
OptiMag folair magnesium – https://bit.ly/3VGuVTU