We were all a bit shocked by events in Christchurch, though luckily Liz’s family are all safe. Liz has been saying for months that they were expecting another big earthquake, but I am not sure that they expected it to be right under the city centre.
I wanted tell you about the trees we have planted because, as any walker knows, wind has a material effect on temperature. I was reading this week that winds as low at 11-14km/h can significantly affect the temperature in a vineyard. As I have been explaining in previous blogs, Rathfinny benefits from have a ridge of the South Downs, just to the south of us, which will shield us from the worst of the prevailing SW winds. However, the fields are still exposed to winds blowing up and down the Rathfinny valley and up the Cuckmere valley. So we decided we needed to plant three windbreaks on the first parcel of land destined for grapes, set 270 metres apart. It’s a tricky business to decide where and how many to plant. The theory is that you get a 60% reduction in wind speed at distances of up to 10 times the height of the tree. So assuming these trees grow to 15 metres then we will get a 60% reduction in wind speeds 150 metres away. However, you still get 10% reduction some 300m away. And then the next line of trees has the effect of lifting the wind again over the next windbreak.
The fact is that some wind in the vineyard is good news. Wind helps dry out the leaves and fruit after rain and so reducing humidity and disease risk. However, wind also lowers temperatures and can close the stomata on the bottom of the leaves, which reduces photosynthesis and respiration. It’s a balancing act. Disturb the wind but don’t reduce it so much that we increase the risk of disease.
The Met office data we have shows that although we may experience average winds over the site of 13.6 km/h during whole the year, during the growing season, April – October, we only experience average wind speeds of 12 km/h. The critical times are flowering in May/June and the ripening period called Veraison, from the end of July onwards.
We thought it was important to plant native trees, so we’ve gone for a mix of broadleaf species that grow well in chalky soil and exposed sites: Ash, Beech, Field Maple and Hawthorn. We resisted planting some of the faster growing varieties like Italian Alder and Eucalyptus principally because they are not native and because they don’t like chalk. Hopefully these windbreaks will help break-up the wind and increase the average temperature in the vineyard so increasing fruit quality.