Hazel catkins: what they tell us about the weather

Martha Boalch, 21/12/2018

What are catkins?

Catkins are the inflorescences, or clusters, of single sexed flowers.  Hazel trees have catkins with male flowers. The female hazel flowers are separate and much smaller. They look like little brown buds with crimson red styles that protrude out to catch the pollen. Get our top hazel identification tips.

hazel too early

Male hazel catkins, before flowering, Margaret Burton

catkins flowering

Hazel catkins flowering, WTML

female hazel flower

Female flowers of hazel with crimson filaments, Tony Beyga

What are we recording?

Hazel catkins will appear on the tree towards the end of autumn. However, this is not the date we are recording on Nature’s Calendar. The event we ask people to look for is the first time they see these catkins flower – they go a yellow-gold colour, swell up and open out and you may event see pollen being blown out by the wind.

Do they open first in the south?

Each year our recorders send in the date they see their first local hazel catkin swell and release pollen. This tends to produce a marked pattern, the first dates coming from the south in December and January, and then spreading to the north over the next few months.

Maps showing the distribution of hazel first flower records at the start of 2018

1 Jan 2018

1 Jan 2018, most records towards the south

15 jan

15 Jan 2018, more records and spreading north

1 Feb

1 Feb 2018, more results in Scotland

15 FEb 2018

15 Feb 2018, lots more from everywhere

You can experiment with our live map tool on our Analysis page.

Is hazel flowering earlier?

The graph below shows the last 19 years of data for hazel. Each year has the average first flower date for hazel plotted as the number of days after the 31 December.


You can see that the latest date and highest point on the graph is the date for 2001 – 61 days into the year which was 2 March.

2018 is among the three earliest years, along with 2014 and 2007. This may come as a surprise as most will remember a cold and snowy spring 2018. In fact, December and January were mild in temperature and this allowed various early spring events to occur earlier than normal before the snow struck.

The trend line on the graph shows that, even over this relatively short time, hazel flowering appears to be getting earlier according to our data.

Send us your hazel flowering dates

By submitting you records of hazel first flower you are adding to the biggest data set of its kind in the UK. This data supports scientists studying the impact of changing weather and climate on wildlife.

Download your free desktop calendar to brighten up you PC and remind you what to look out for.

Join thousands of other people and let us know what's happening to wildlife near you.

Join thousands of other people and let us know what's happening to wildlife near you.

Have you seen your first butterfly or swallow of the spring? Is it a good year for wild autumn fruits? Take part in Nature's Calendar and help scientists to monitor the effects of climate change on wildlife.

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