Winter Chill - why a warming climate may not be so hot for your fruit crop

For a few years now, some UK fruit growers (particularly blackcurrants and hops) have been concerned about rising winter temperatures. Their worry is that inadequate winter chilling may be interfering with the normal processes of reproductive development and therefore the subsequent yield. So here at East Malling Research we’ve been looking into whether this is a significant issue for fruit growers now and whether climate change is likely to make it even more of an issue in the next few decades.

So what have we found? We can see that there has been a significant reduction in levels of winter chill in recent years. When we compare temperature ranges from 1969-79 to 1989-99, we’ve seen a reduction in chilling hours of 5.7% in Tayside in Eastern Scotland and 12% in Kent, whilst the incidence of spring frosts over the same periods has declined by 31% in Tayside and over 50% in the West Midlands.

And this trend is set to continue given our warming climate. Using the UK Climate Impacts Programme (UKCIP) projections, winter chill will decline by 2080 by 20% in Tayside and 31% in Kent, in a low emissions scenario*. Under the high GHG emissions scenario, these figures jump to a decline of 37% in Tayside and 59% in Kent. Both scenarios present serious challenges for fruit growers, breeders and researchers.

But what does this mean in practice? Depending on your location in the country, rising winter temperatures could mean different things to different growers – for those in a more southerly location, it could mean you need to look to new varieties to suit these changing conditions. For those further north where the reduction in winter chill is not so great, the warmer weather and longer growing seasons could have a beneficial effect on yield. More local conditions will also have an effect on this.

But for both, a greater awareness of the winter chill factor can only benefit your business. Over the last decade or so, winter chill has become an unfashionable area of research with the result that many propagators have no idea what the winter chill requirements of their products are. As a grower, it pays to know this and choose the right variety for your location and needs, especially where you are planting crops that you expect to be in the ground for the next 20 years.

There’s a real need for more understanding and research into this area, but as a grower you can be better informed by knowing the right information and asking the right questions. Measure what the winter chill factor is at your site, and ask your propagator the winter chill requirements of the varieties they are offering you.

Dr Chris Atkinson is Head of Science at East Malling Research, which provides research, innovation, and science-based solutions to enable sustainable horticulture and to develop land-based industries.

Take a look at our story about Edward Thompson of Pixley Berries in Herefordshire, who has developed a profitable new blackcurrant variety in response to climate change. And if you have a story about how you’re adapting to climate change, let us know and we'll publish it on the site. 

*UKCIP provides information on how the UK’s climate is likely to change over the next few decades to 2080, offering different projections according to three different ‘emissions scenarios’ – whether we’ll be pumping high, medium, or low levels of greenhouse gases (GHGs) into the atmosphere, and the projected climate change generated by those levels of emissions. 

Image courtesy of Rose Bridger on Flickr