Fog. Planes grounded. Finally, it seems, autumn has arrived, although down here in the south of England the temperatures still aren't exactly teeth-chattering. No sign yet of the predicted icy winter. This could be a worry for apple growers, as sufficient chilling is regarded as necessary for most apple cultivars to set blossom the following year. The snowy winters of 2009 and 2010 had a hand in some bumper harvests.
The excellent Orange Pippin gives details of the minimum chill requirements. Apple trees generally need around 1000 hours at temperatures between 1°C and 7°C (33-45°F), though there are “low-chill” varieties, such as Anna, that require only 300 hours.
Before we worry, though, about whether Granny Smith is going to get enough sleep this winter, here’s something that Jim Hester, a certified nurseryman from California, said back in 1996 when the state enjoyed unseasonably warm weather. While farmers fretted, he reassured home growers: “Most people probably won't notice. For the farmer, a full crop can mean everything, but for the home grower, whether you get 100 pieces of fruit on your tree or 85 isn't going to make that much of a difference.”
Meanwhile, apple expert Kevin Hauser, who also writes the informative Apples and Oranges blog, thinks that far too much emphasis is put on temperature. In fact, a recent posting derides experts who quote experts on the chill factor, without having any experience, and shows a Dixie Red Delight cropping on only 250 chilling hours. He writes: "The truth is the chilling hour needs of different apple varieties are not known and cannot be speculated, and the only way to find out is to plant it somewhere warm and see what happens... More often than not, the chilling requirement is much, much lower than anyone would have guessed."
He and other growers in the region have another theory, too. The Sandy Bar Ranch quotes his opinion that leaf drop, and not low temperatures, triggers dormancy. Dormancy is characterised by leaf drop, so it seems that it can be induced, whatever the temperature, by removing the leaves oneself.
So those of us who'd like to maximise our crop in these cash-strapped days can do more than hope for cold weather. So far temperatures haven’t risen so much that apple trees don’t lose their leaves in this part of the world but, while my russet has only a few yellowing leaves lingering on the branches, my Bramley is fully clothed and green. If its leaves don't drop soon, I'll consider stripping them off, just to make sure.