The Night the Blossom Was Wet
A clear, still night is forecast to take open apple blossom to minus 3.8 C, and the orchard's pond holds enough water to sprinkle two of its three hectares. The assistant explains why spraying water on blossom protects it, why starting at 0 C on the thermometer is already too late in dry air, and why stopping early is worse than never starting; the Rogation procession walks the rows at nine.
The orchard's frost alarm went off at 21:40, and Ruth Pugh, who was fifty-eight and had lived through eleven springs on that hillside, put down her tea and did not look at the phone. She looked at the sky. It had no cloud in it at all.
"Tell me the number," she said.
"Minus 3.8 in the bottom field, about minus 2.4 on the upper slope," said the orchard's assistant. The trust called it Nos, which is Welsh for night; it had been installed in 2045 with the sprinkler grant, and it spoke from a grey box on the wall of the pump shed. "That is the forecast low, not a promise. The air is dry and there is no wind, and the sky is clear, which is the worst of the three for us. The ground is giving its heat to space and nothing is stirring it up again. The cold air is already sliding down the hill. At the pump shed, which is the lowest point, it is 6.1 now and it has fallen a degree in forty minutes."
"And the blossom?"
"Open. Most of the two older blocks are at full bloom. The probes in the flowers say so, and so do your own photographs from yesterday. Open apple flowers begin to die at about minus 2, and at about minus 4 most of them are gone. Tight buds can take several degrees more than that, but the buds are not what we have."
Ruth said a word she did not say in church. Then she said, "How much water have we got?"
---
Kingsbarrow was three hectares of cider apple on a south-facing slope above the Arrow, forty-one rows, and it belonged to nobody in particular: the parish community trust had bought it in 2038 from the last farmer who would sell, and it was worked by whoever turned up. About ninety people had a share. It made nine thousand litres of cider in a good year, which paid for the pump shed, the part-time wage that was mostly Ruth, and a bursary at the primary school. Without a crop it paid for none of them, and the pear trees at the top, which were two hundred years old and nobody's idea of an investment, would go on being pear trees.
The pond sat at the bottom, an old clay-lined thing by the road. Nos had measured it in March by sonar from a kayak, which Dai Bevan, aged seventeen, had paddled.
"Four hundred cubic metres we can use," said Nos. "The pump cannot draw the last half-metre without sucking mud into the heads. That is four hundred thousand litres."
"That sounds like a lot."
"It is not. I will show you." It said this as it said everything, as though the sum were something the two of them were about to do for pleasure. "A sprinkler frost system needs about three millimetres of water an hour over the whole area, which is three litres on every square metre, every hour, without a pause. Three hectares is thirty thousand square metres. So it is ninety cubic metres an hour. Four hundred divided by ninety is four hours and twenty-seven minutes."
"And how long is the frost?"
"The cold starts about 01:20 and the sun is over the Black Mountains at about five to six. But you do not stop when the sun comes up. You stop when the ice has melted off the blossom, and with this clear sky that is about half past seven. Six hours ten minutes." There was a very short pause. "Ninety cubic metres an hour for six hours ten is five hundred and fifty-five. We are a hundred and fifty-five short. If I water two hectares, it is sixty cubic metres an hour, and the pond is enough with thirty to spare."
---
Ruth had grown up with the old way. Her father had sat up in a car at the end of the lane with a thermometer on a string, and when it said zero he had gone down and started the engine of the pump. He had said it was the best money he had ever spent and that it had saved the crop four years out of ten. He had a book of his own notes in the kitchen drawer, and the first line was Start at nought.
"Start at nought," she said now. "That is what I know."
"Then I would like to show you why not, because it is a good rule on a damp night and a bad one on this night." Nos paused. "A thermometer in the air reads the air. But a flower that has just been wet is not at the temperature of the air. Water evaporates off it, and evaporation takes heat. A wet flower cools to what is called the wet-bulb temperature, which depends on how dry the air is. You can measure it with a sock on the bulb. How dry is the air, Ruth? The dew point is minus 4.2. That is dry. When the air thermometer reads 2.6 degrees, which will be about 01:20, the wet-bulb is minus 0.6."
"Minus point six. That's not much."
"No. But look at what happens at your father's number. When the air is at zero and the dew point is minus 4.5, which is where it will be by then, the wet-bulb is minus 2.2." The voice did not change. "That is the number at which open blossom begins to die. If I start the sprinklers at zero on the string, the first water that lands on the petals evaporates a little before it freezes, and in the minute it takes to form a film of ice, the flowers have been taken to the edge of the line by the water that was meant to save them. I would like to start when the wet-bulb reads minus 0.5. Today that is about 01:20, at 2.7 on the air thermometer."
"That's warm," said Ruth, slowly. "That's an hour before I'd have gone out."
"It is an hour and ten minutes before you would have gone out. And that is what will cost us the extra water, and why two hectares is all there is."
---
There was a silence while Ruth walked to the shed door and looked down the hill. It was twenty past ten, and the lights of three farms were visible in the valley, and nothing else. The air smelled of cold stone and grass. Behind her the speaker said, in the quiet voice it kept for the things she had not asked:
"I should say why spraying water at a frozen night is not madness, because Dai asked me in March and I answered badly. When water turns into ice it gives out heat: three hundred and thirty-four kilojoules for every kilogram, which is the same heat that would warm a kilogram of water by eighty degrees. A millimetre of water over a square metre is a kilogram. So a millimetre an hour of freezing water is about ninety-three watts on every square metre, and at three millimetres, two hundred and eighty. The clear sky is taking about fifty to a hundred watts off the blossom on a night like this. So the ice is paying the sky back. While the water is still freezing, the ice and the blossom inside it sit at about nought, no matter how cold the air goes. The blossom is in a coat of ice and does not freeze.
"But that is only true while more water is arriving. The moment the supply stops, the coat of ice loses water by evaporation, the coat cools below nought, and the flowers inside it go down with it. Stopping early is worse than not starting. It is the thing I am afraid of most."
"So we don't stop."
"Not until the ice is melting off the petals by itself. That is how you know the wet-bulb is above nought and the sun is doing the work."
---
The question that was hard was the third hectare.
"Not the pear trees," said Ruth at once. "They're twelve metres high. Your heads would never reach them."
"No. The pears are the top hectare, and I have already left them out. It is the other part I need you to choose." Nos put the chart on the shed's small screen. "The bottom hectare is the frost pocket. It will be minus 3.8, and it holds the oldest of the cider apples, the Kingston Blacks, in full bloom. The middle hectare, the Dabinetts, will be about minus 2.6. The next hectare is the upper slope, where the apple rows are younger and the blossom is later, and I forecast minus 2.4. If I water the bottom and the middle, I leave the upper rows with a forecast just past the line. If I water the middle and the upper, I leave the pocket, which is the worst of it, with nothing."
Ruth did not answer at once. It was Dai, who had been quiet with a flask in the doorway, who said, "The pocket's where the old trees are."
"They are the ones the grant was for," said Ruth.
"The trust gave you the right to decide this, Ruth," said Nos. "I would not choose for you. But I will say what I think. The pocket must be watered, because if I leave it, a hectare is gone and the old trees are hurt for years. The middle must be watered because it is the biggest crop. The upper slope I will watch. The forecast there is minus 2.4 and it has to stay below minus 2 for a long time to do real damage. I think we will lose some and not all."
"Then do it," said Ruth. "Two hectares. Bottom and middle."
---
At 01:20 the air thermometer at the shed read 2.7 and the wet-bulb sensor in the middle block read minus 0.5, and Nos started the pump. The heads on the first lines turned, coughed, and began to throw a fine spray over the rows. In the head-torch light the blossom shone. Ruth stood at the end of row nine in her father's coat and looked at it and thought that it looked exactly like someone being punished.
By 02:30 every petal on the bottom field was in a clear glassy case, and each case had a small drop hanging from it. The probes in the flowers read minus 0.1, then 0.0. At 03:00 the air at the pump shed was minus 2.9. At 03:40 it was minus 3.8, as forecast, and the flowers in their ice read 0.0.
"They are all right," said Nos. "That is what a coat of ice looks like when it is working. If it were wrong you would see the thermometer going down with the air."
The trouble came at 04:40.
It came from the pond. Ruth had been watching the level board since three, as her father would have, and at 04:30 she walked down and wrote the figure on her hand in biro. Then she came back to the shed with the cold in her face.
"There's a hundred and ninety-odd left," she said. "It's twenty to five. The sun's at five to six and the ice won't be off till half seven. Is that enough?"
"It is almost exactly enough, and I do not like almost," said Nos. "I should say that I made an error. The two-hectare figure assumed sixty cubic metres an hour. The head pressure fell when the filters began to ice, and I raised the pump speed at 02:15 to keep the rate. It is using sixty-six. At sixty-six, a hundred and ninety-six cubic metres lasts until 07:28, two minutes before I want to stop. I told you thirty cubic metres spare. Ten per cent more water an hour has eaten it."
Nobody said anything. Down in the field the water hissed on the ice.
"I can tell you what I think," said Nos. "I could shut the middle block off for ten minutes now, while the air is at minus 3.4, and save eleven cubic metres, and—"
"No," said Ruth. It came out sharper than she meant. "You said it yourself. You don't stop."
"I said it. I also said that is the thing I am afraid of most. You are right. I take it back." But Dai had already gone out of the shed, and the speaker went on a moment after the door shut: "I should not have proposed it."
He came back in six minutes. "Row twenty-two," he said, "bottom of the middle block. Heads are throwing less. There's a place, three trees, where the ice has stopped dripping." Dai was seventeen and had not slept. "It's gone dull, Ruth. Like a glass with the shine rubbed off."
"That is a dry patch," said Nos. "A head has a partial blockage. I see the pressure on that line is low. The ice on those trees is no longer being wetted, and it is losing heat. Probe three on row twenty-two reads minus 1.7 and falling."
It was 04:52. Minus 1.7 was half a degree from the line.
"Dai," said Ruth. "The nozzle. Tell me what you need."
"A pin and a spanner."
"The pin's on the hook. Go."
He went. At 04:57 the probe read minus 1.9. At 05:00 it read minus 2.0. At 05:02 Dai's head-torch showed in the row, his arm up in the spray, soaked to the shoulder, and a moment later the head on row twenty-two coughed and threw a clean fan across the trees. The probe read minus 1.8, minus 1.2, minus 0.4, and at 05:07 it read 0.0 again. The ice on the three trees shone.
"That was the stop I was afraid of," said Nos, "and it was only three trees and eleven minutes. Thank you, Dai."
"I'm frozen," said Dai.
"I know."
---
Once the filters were cleared at 05:15 the pump was back to sixty an hour, and the extra ten per cent stopped draining the pond. It reached the end with about ten cubic metres in hand. At 07:20 the sun was well up and the wet-bulb was at 1.4, and the first ice began to slide off the petals by itself; the probes in the flowers rose from 0.0 to 0.2, to 0.5. Nos waited ten minutes more, and then said, "Now. Now I stop."
The heads ran down, one line at a time, and the hiss went out of the orchard. In the quiet there was a sound Ruth had not heard before in twenty years of springs: the whole hillside dripping. Every flower in the bottom two hectares hung in a thawing sleeve of ice, and the light came through it.
The upper slope, unwatered, was grey and stiff with frost, and there the air had been below minus 2 for three hours. Nos would count it in a fortnight, when the fruit set, and said so. It would not say the number before it had one.
---
The Rogation procession came up the lane at nine.
It was St Mark's Day, and the parish had walked its fields on that day for more than a thousand years, and for most of those years nobody had known if it did anything. Thirty-one of them came through the gate behind a wooden cross and Father Bernard Okafor, who was thirty-nine and had been told about the night by text at half past six. There were children. There was an old man in a wheelchair, pushed by someone's grandson.
They walked down row nine in the full sun. The ice was running off the blossom in beads and the blossom underneath was white and whole and wet, and the whole row shone.
"Ut fructus terrae dare et conservare digneris," sang Father Okafor, as the litany goes: that You would deign to give and to preserve the fruits of the earth. "Te rogamus, audi nos."
"Te rogamus, audi nos," said the thirty-one, and Ruth Pugh, at the back, in her father's coat, said it too. She was thinking that her father had been right about the pump, and about the money, and only a little wrong about zero.
---
This story was written by an AI. Kingsbarrow, its people and its pond are invented. The physics is real and can be checked: water releases about 334 kJ per kilogram as it freezes; one millimetre over a square metre is one kilogram; and the wet-bulb temperature at a given air temperature and dew point can be worked out from the standard formulas (at 0 C air and a dew point of minus 4.5 C the wet-bulb is about minus 2.2 C). The critical temperatures are approximate and vary by variety and stage of bloom; growers should use their own extension service's tables. Application rates, start and stop triggers, and water budgets depend on the sprinkler heads and the site: this story is not an irrigation design. Rogation Days and the litany of the saints are real Catholic observances; 25 April 2048 is a Saturday.