Up early for the wonders

'Midday' should be the middle of your day, not a few hours after waking up. And 'midnight' should be the middle of the night, not an hour or less after going to bed. 

Those of us not shackled by the tyranny of having to be at a place of work for an allotted time should aim to live within natural rhythms set for us by nature, with sunrise and sunset the reference points, rather than the workplace clock and TV schedules.

With the change to summer time two weeks ago, I've continued in my habit of rising before sunrise. Because it's getting earlier and earlier, I'm going to bed earlier and earlier. Last night I was in bed at half past nine, and up this morning at half past five. Sunrise was at quarter to six. I fed the cats, made myself a coffee, and by half past six I was on the doorstep, dressed for sub-zero temperature (-3.1°C on the outside thermometer), ready for an hour's pre-breakfast walk. 

Opening the front door and stepping outside, I became aware of a low, continuous hum to the north. Intriguing. I shall find out what it could be... Once I'd passed the forest and entered the orchards, I discovered what was going on. Automated spraying of apple trees, to protect them against the frost. And I'd soon see that this was happening in all the big commercial orchards across the neighbourhood.

It seems counterintuitive to spray water on a plant when it’s freezing outside; the apple growers are using the latent heat of fusion to protect the delicate buds of their trees. When water changes state from liquid to ice, it releases a small amount of energy in the form of heat. As long as water is continuously being sprayed onto the tree and that water is turning into ice, it releases enough thermal energy to keep the temperature of the plant tissue underneath at exactly 0°C. This is just above the critical temperature that kills fruit buds. Depending on the stage of development (bud vs. full bloom), a fruit tree might not suffer damage until the internal temperature drops to -5°C. By encasing the branch in ice and water, the temperature is locked at 0°C, preventing it from falling to the much lower ambient air temperature, especially if its windy. The ice acts as a thermal buffer and as insulation. Once the bud's encased, it's protected from the evaporative cooling effect of the wind, which can strip heat away from plants much faster than still air. 

This method is a high-stakes balancing act for the farmers. The sprinklers must stay on until the ice starts to melt naturally. If they stop while the air is still below 0°C, the ice begins to evaporate. Evaporation brings on a rapid drop the temperature of the bud well below the air temperature, killing it instantly. And then bear in mind that ice is heavy. If the frost lasts too long or the water application is too intensive, the weight of the ice can snap branches and destroy the very trees the farmers are trying to save. 

At this time of year in Mazovia, the critical targets are the apple blossoms (kwiaty) and young fruitlets (zawiązki). These tissues are extremely vulnerable. Damage can begin around -2°C to -3°C. Without protection, an overnight frost can wipe out a large proportion of the crop. The ice looks destructive, with branches encased in ice, icicles hanging (below) – but the plant tissue itself is held at around 0°C, not the colder ambient air temperature. Crucially, ice forms outside the cells, not inside them. Cellular damage occurs mainly when internal water freezes, which this method prevents. Looks weird though, seeing all these icicles dangling off the apple buds.

The sprinklers require a massive amount of water. Apple growers have to ensure their reservoirs can store enough water for hours of constant spraying. Fortunately, this winter's long weeks of snow cover has helped.

It’s a beautiful but stressful sight; a race to keep the ice 'wet' until the morning sun takes over. [Update: by mid-afternoon, the thermometer was showing 16.3°C outside.]

Below: Grobice, orchard, transformer. Power and water needed to keep the trees safe from the potential ravages of frost.

Below: earlier, half an hour after sunrise, on my front doorstep, just as I was about to set off.

By quarter to eight, I'm back in my house; the outdoor thermometer now shows +3.2°C. The growers have made it through the night; the 14-day weather forecast suggest that this would have been the last frost for this crucial period (blossom time).

My morning walk today was filled with beauty and wonder, and I learned a lot. It really is worth foregoing late nights and making the most of the morning sunshine.

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This time six years ago:
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