Blackcurrant chilling hours tracker

Calculate your blackcurrant chill hours

This tool calculates chill hours and will help you to predict the levels of bud break you are likely to see in your crops. It will also help you make informed decisions and direct the use of dormancy-breaking treatments to increase yield and quality should you wish to.


It is well established that plants need to experience cold periods.  The trend towards warmer winters has had a negative effect on dormancy bud break in blackcurrant. There is increasing evidence that the amount of cold experienced by blackcurrant cultivars is inadequate in some regions, during some winters. This leads to delayed and uneven bud break and can cause poor yields and quality, substantially reducing profitability.

How does the calculator work? 

This tool enables you to track the accumulation of chilling hours for the current season. It is based on the number of hours since 1 October 2020 where air temperature did not (or is not expected to in the next two days) exceed 7 °C.

Location colours on the map indicate the relative degree of chilling experienced since 1 October 2020:

  • Bright red – fewest accumulated chilling hours
  • Blue – most accumulated chilling hours

11 additional locations in the key regions have been added for the 2021 season.

You can see the accumulated chilling hours for one, or more, locations in the graph. The dotted horizontal lines indicate the threshold chilling total needed for varieties that have either a low or high chilling requirement.

For locations in the key blackcurrant growing areas you can also compare the chilling hour accumulation in different years. The tool will be updated daily until end of March, useful for varieties with late bud-break.

Blackcurrant Chill Hour Calculator

How to use

Current season 

By default the dashboard shows data for 27 locations in the key regions. To show data for ~150 locations across the UK, select ‘Current season (all regions)’ from the top left, then click the 'GO' button

Display the accumulated chilling hours for a particular location in the graph by clicking the coloured dot on the map. Select more locations by holding the ‘Ctrl’ button or using the 'Rectangle select' button on the map

In the 'Current season (key regions)' view, each line in the graph represents a single location but in the 'Current season (all regions)' view each line in the graph represents the average for all selected locations in that region

In the 'Current season (all regions)' view, locations can be filtered by country and region (England and Scotland only) by selecting from the dropdown list

You can move the ‘Date range’ slider to compare how much chilling occurred over a particular time interval

Move the ‘Chilling hours’ slider to check which locations / regions have accumulated more or fewer chilling hours than a particular threshold. Note that the ‘Chilling hour’ slider represents the total up until the last date in the data and is not updated by changing the date range using the ‘Date range’ slider.

Cross-season comparison 

  • Select ‘Previous seasons (key regions)’ then click the 'GO' button to show a comparison with other years for a subset of locations in the key regions
  • You can choose different years from the Years dropdown box
  • Clicking on a year in the legend above the graph will highlight the corresponding line in the graph
  • Note that each line represents the average for all locations selected on the map. Due to missing data, not every location is necessarily included in every year.

Hover over the locations on the map and the lines in the graph for more information.

Blackcurrant varieties and chill requirements

Different varieties of blackcurrant have different chill requirements. The table below indicates the number of chill hours required by some of the most commonly grown varieties in the UK.

Blackcurrant variety indicative chill hours


Blackcurrant Variety

Approx. Chill hours < 7°C Oct - March

Ben Gairn


Ben Vane

c.a. 1400

Ben Lawers

c.a. 1500

Ben Starav


Ben Lomond


Ben Hope




Ben Dorain


Ben Klibreck


c.1800 from field experience

Ben Alder


Ben Avon


Ben Tirran



This table is based on research conducted as part of SF 012 (GSK194), SF 012 (GSK215) and SF 012 (GSK225) by John Atwood and from field experience.


Using historic chill data along with the winter chill requirements of different varieties can help you decide which potential cultivars to plant. Planting unsuitable cultivars can result in uneven bud break, uneven ripening and poor yields and should be avoided.