Understanding what went right and what went wrong in a particular season on the allotment is helped by comparing the weather in each moth with the long term averages. We are lucky that there are a few met stations in the area, at which data have been recorded for over 40 years. The figures below show the weather for Boxworth, which although a few miles away, reflects pretty well the weather we experience in St Ives.
One important feature of our weather in 2010 was that it was actually a dry year. If your plot was flooded you may not feel this was the case, but the first figure below shows the picture. There were two very wet months – February and August. However taken over the whole year, we only had 500 mm or 90% of the normal rainfall (long term average 557 mm) in 2010. If we take out those two wet months, then the remainder of the year only had 63% of normal rainfall. Therefore the main problems we had were flooding February (made worse when the snow for January had melted), and ponding at the bottom of the meadow (new plots) at the end of August/early September, when people were still driving into the plots and some peoples cars got stuck at the bottom of the meadow !
However it is dry weather which is the main thing limiting growth of vegetables and will have had the biggest effect on success. The key months after we have sown our seeds are March through to July, and these months only had 50% of normal rainfall in 2010. Early potatoes in particular suffered last year from lack of water. However the late rain in August probably helped later maturing crops like squashes and sweetcorn.
So what about temperatures ?
Again while we remember the extremes (very cold temperatures in January and again in November, December) these were not the main features of the growing season. The second figure shows the average maximum and minimum temperatures for each month, which simply reflect day and night time temperatures. We can see that April was relatively warm. Because the last hard frost (-3.2 deg C) was recorded on 8th March, this meant that fruit trees managed to get through the blossom period without any damaging frosts and we had good crops of apples and plums. However there were another eleven cold nights when temperatures hovered around freezing (dropping below 1.5 deg C but staying above zero), including three successive nights on 10-12th May, which is probably when a lot of early potatoes suffered blackened leaves.
As noted above, fruit set on apples and plums had been excellent, and next good thing was that the cool nights meant we did not suffer from an early attack of codling moth. This pest tends to build up when night temperatures get into double figures. After a period of seven days from the 5th June when night temperatures hovered between 10 and 14.5 deg C, we did not get to consistent night temperatures above 10 degC until the 22nd June. Monitoring of codling moths using a pheromone trap on plot 50 showed clearly the explosion in moth numbers after 28th June. Anyone wanting to control this pest should have sprayed about the 12th of July – probably later than in many years.
The last interesting feature of the growing season was the low maximum temperatures in August and September. These cool days would most likely be associated with the high rainfall and hence lack of sun experienced on days when it was raining. Finally as we went into October and November cold and wintry weather set in, and leeks and parsnips froze into the ground. If this pattern of weather continues we may have to re-learn clamping of vegetables to keep an easy supply over winter. So to end the season, we had no more flooding, because the last two months of the year were dry, which tends to be a feature with very cold wintry weather.
So, overall a cool and dry year. But what will next year bring ? Hopefully not codling moths, their appearance last year being as shown below.
Any questions or comments, please contact me at richard.weightman@ntlworld.com.
Richard Weightman
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