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.


This tool enables you to track the accumulation of chilling hours for the current season. You can also compare the chill hours in your location with last year’s data.
Location colours on the map indicate the total chilling hours accumulated since 1 October 2019.

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

You can see the accumulated chilling hours for one, or more, locations on the graph. The lines indicate the threshold needed for varieties that need either low or high chilling hours. 

The tool will be updated daily until end of March, useful for varieties with late bud-break.

How to use


  • Click ‘All locations’ to show the 140 locations where we have data
  • Choose one or more locations on the map – use the ‘Ctrl’ button to select multiple locations
  • To select a region, choose from the dropdown list once you’ve clicked ‘All locations.’ This will display accumulated chilling hours in the graph. 

Note that 19 locations will be shown by default. 16 Met Office sites and 3 grower locations. Only 23 locations can be shown on the graph.

Cross-season comparison 

  • You can choose different years to compare data
  • Click ‘Multiple seasons’ button and a dropdown list will appear
  • If you click on a year in the legend above the graph, it will highlight the corresponding line on the graph

Note the line represents averages for all locations selected on the map. It’s possible that, due to missing data, not every location is included in every year, so the average lines are approximations.


  • You can move the ‘Date range’ slider to select date tailored to your specific scenario. 

Note this is for the current season only. Weather data from grower locations is only available up to the end of February.

Accumulated chilling hours 

  • Move the ‘chilling hour total’ slider to exclude locations on the map
  • You can also exclude details from the graph below or above a chilling hour threshold.

Note that the ‘Chilling hour total’ slider represents the total up until the last date in the data and does not get updated by changing the date range using the ‘Date range’ slider.

For more information you can hover over the buttons, the locations on the map and the lines in the graph.

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.