The problem is no longer simply how much water growers have, it is whether they can get enough water to the crop, quickly enough.

Paul Goddard, Business Development Manager at BASF spoke to Mark as part of the Perfecting Potatoes Together initiative to share some insights to support growers’ thinking this year, next and beyond.

For years, the ‘standard’ water requirement for potatoes has remained the same. Roughly 25mm of water is required per week to satisfy the crop’s yield potential. However, the 2026 dry season has seen one of the most significant changes in the history of potato production in the UK.

In a prolonged period of dry weather, Mark has demonstrated that a potato crop can use up to 6–7mm of water a day.

“To give a potato crop the best chance in a season similar to the one we have been experiencing, an inch or 25 millimetres of water is now required every four days,” he says. “And that's pretty astounding when growers realise that they can't irrigate their whole crop every seven days, let alone every four.”

On a light sandy soil, the challenge becomes more acute. At around 32°C, Mark estimates that the soil may have only 12mm of readily available water before the crop begins to experience stress, effectively requiring irrigation every two days to maximise yield.

This presents a new challenge for growers: it is not simply about having a licence, reservoir or irrigation system, but ensuring they have the capacity, infrastructure and operational flexibility to put water onto the crop when it needs it most.

For some, the strategy has been to hold back water in case they need it, but for Mark this feels counterproductive, as once the crop is under stress, yield potential is already being compromised.

“If you've got water, use it when the crop actually needs it and you'll get the biggest yield response,” he says.

“That means applying water when the crop first comes under stress, and then again when it needs it, rather than preserving water for a theoretical ‘rainy day’.”

The economics of irrigation make that even more important. Mark argues that infrastructure represents a significant fixed cost, so unused capacity is expensive and a waste. Growers with water licences could be making more use of the opportunity to develop strategies to protect the crop.

“If you've got a licence, pump it,” he says. “Pump it somewhere. Give it to your neighbour. Move it from one stream to another. Put it in a reservoir. If you're not using it, somebody or another industry will come and take it away.”

Drip is not automatically the answer

Drip irrigation has major potential, particularly where water can be delivered precisely to the crop. But Mark cautions against treating it as a universal solution.

Drip operates at low volume and low pressure, meaning existing high-pressure systems fundamentally need to be redesigned rather than simply adapted. Pump efficiency can also suffer when pressure has to be stepped down substantially. The high fixed cost of laying and installing drip means that its cost per millimetre becomes particularly high if the system is not used frequently.

Overhead irrigation also has its own limitations, as Mark explains.

“On a 29°C day, it is estimated that evaporative losses from sprinklers are at around 5%. In hotter conditions such as 37–38°C, with moderate wind, the potential loss is between 12 and 18%, but losses from large-nozzle rain guns are <10%. This highlights the importance of understanding the irrigation system, the crop, the soil and the economics as a whole, rather than just focusing on the technology.”

Build the canopy — then keep it alive

Mark describes the first irrigation events as critical to building the crop's “solar panel”, allowing the canopy to capture energy and ultimately driving tuber production.

“In a typical maincrop situation, two irrigation doses separated by around 7–10 days can help take ground cover from roughly 30% to 70–80%, then towards full canopy. But once that canopy has been built, the water requirement does not disappear. It increases because the crop now has a large evaporative surface to maintain.”

That is one reason the rainfall received in early June was so important in 2026. Mark argues that without the 30–70mm received across much of the UK during the first ten days of June, many crops would have struggled to establish the canopy needed for high yield. The rainfall effectively removed the immediate need for second and third irrigations, giving growers valuable time.

But, once that canopy is established, the crop must be supplied, further demonstrating the challenges facing many potatoes this season with access to water not available.

A shorter season makes speed critical

For Paul Goddard, BASF’s Development Manager for Potatoes, a shorter, more water-constrained growing window means other agronomic decisions must support rapid, even establishment rather than being considered in isolation.

“For both determinate and indeterminate varieties, we've seen real benefits from using the Xemium-based ALLSTAR in-furrow – it gets the crop off to a good start.” he adds.

“In some seasons, emergence has been more than a week ahead of other in-furrow treatments, which can increase the proportion of tubers within marketable grades. It is worth remembering that a week of light interception in June is worth three weeks in September.”

Mark highlights the impact of the crop's physiological clock effectively running faster.

Bright, hot conditions can allow potatoes to accumulate yield rapidly, provided water remains available. But a shorter effective growing season means there is less time to recover from water stress.

That has implications for planting dates, variety choice and harvest planning. Mark points to the contrast between determinate, shorter-season varieties and longer-season indeterminate varieties.

“Longer-season types may have greater opportunity to continue rooting and potentially capture later rainfall, but that does not mean they automatically convert access to water into yield. They remain dependent on adequate water supply if their yield potential is to be realised and stress avoided.”

Mark warns that drought-stressed plants can have weakened defence mechanisms and may become more vulnerable to invasion by pathogens. At the same time, extremely dry conditions can suppress the development of other diseases.

That means symptoms appearing during a drought should not automatically be interpreted as evidence of a pathogen. Physiological stress, nutrient limitations and disease can overlap, particularly because nutrient uptake itself depends on water availability.

That makes establishment and disease control part of the same water-management strategy. Where irrigation capacity is stretched, solutions that help the crop establish quickly, evenly, and make better use of available moisture, are an increasingly good fit.

Paul notes that ADAS trials in other crops have shown Xemium-treated crops deliver enhanced water-use efficiency and higher yields, without additional water.

“Because the stomatal response and water-use efficiency benefits arise from Xemium’s chemistry, rather than the crop species, ADAS findings provide a relevant basis for considering how ALLSTAR may complement potato programmes designed for a hotter, shorter and more water-limited season.”

Conclusion

For growers, the practical lesson is to diagnose rather than assume, returning to Mark focus on using the science to inform decision-making.

Mark’s overall message is simple, “Growers cannot necessarily rely on the historical assumption that rainfall will arrive when a crop needs it. We need to consider and adapt strategies now, so we are prepared for future seasons. Four of the last eight years have seen crops impacted by weather stress. It is no longer a question of ‘what if we have a dry season’, but more ‘when’."