Advice
December's weather
It’s getting colder
Frost and wind are increasingly common, sunshine hours are much reduced, and it can be bitter. But a few mild days are still likely, and all areas of the UK will see an increase in rainfall. There is a risk of snow, but it rarely lies on the ground for long, except on the highest ground in Scotland, Wales and Northern Ireland. The chance of significant snowfall is less in England, but you never know…
Temperature
Mean December temperatures averaged over the whole of the UK usually vary between a minimum of 1.2°C (34°F) and a maximum of 6.5°C (44°F). However, mild areas such as southwest England can reach 9°C (48°F), and cold areas such as the north and east of Scotland can drop to around freezing for significant periods.
Night frosts are to be expected in all areas except for the mildest coastal regions of southwest England and in the shelter and stored heat of cities.
As for last month, the eastern half of the UK is colder than the west, and the north is colder than the south. However, gales, wind and rain in western regions can make it feel colder than temperatures would suggest.
Frosts will help to improve the crumb structure of previously dug soil, and may kill off some pests and diseases. Tender plants will suffer unless protected.
Rain
Rainfall is quite variable at this time of year. Scotland, Wales and Northern Ireland usually have more rain than England. There have been exceptions, with December 2002 seeing Scotland receive less rain than England.
Rainfall levels are usually quite high everywhere in the UK this month, ranging from around 55mm in East Anglia, to 75-80mm in the Midlands, southern and northeast England, to 140mm in Wales and northwest England, and up to 175mm in northern and western Scotland. However, over 200mm would not be unusual in the Scottish Highlands or over the Welsh hills. Northern Ireland usually receives about 110mm of rain this month.
Take care not to tread on or work the soil when it is really wet - you will likely do more harm than good.
Wind
Gales, gustiness and cold winds are to be expected. This, combined with driving rain or snow, can make for very unpleasant conditions. Frosty days, by contrast, are more likely to be still and clear.
Staking, tying in and protection of plants is a must. The wind can be destabilising, physically damaging, chilling, and very drying for plants.
Winds are usually worse in the north than in the southern half of the UK. They are more severe over high ground, and generally have more force in western coastal regions.
Sunshine
This can be one of the worst months for sunshine levels, approaching the winter solstice. The sun is also much lower in the sky at this time of year, which means that it hits glasshouses at such an angle as to make its transmission and usefulness less than in the spring or summer months.
Mean hours of UK sunshine over December are usually between 30 and 60 hours. The southwest of England and East Anglia usually get the most sunshine, with southern and southeast England not far behind. Central parts of the UK and Northern Ireland usually hover between 40 and 50 hours. Scotland overall has around 30 hours, with northern Scotland getting the least, 21 hours being not unusual.
Visibility can be further reduced by hill fogs and fogs over inland, sheltered areas. These will take longer to disperse in the cold, damp, gloomy weather at this time of year.
Light levels can limit vegetative growth of plants just as much as low temperatures. Giving extra heat to greenhouse plants will not compensate for this lack of light, and your plants may become leggy. Some plants (e.g. poinsettias) respond to reduced light by induction of flowering, or the colouring up of bracts.