It’s icy cold. Last night, the temperature dropped to -5ºC. There’s ice on the pond, and on all our water barrels. A very usual phenomenon when it’s so cold. So usual, we don’t normally think about it, too commonplace. Like why do things fall down instead of up, a silly seeming query which led Isaac Newton to come up with the concept of gravity. In the case of ice on the pond, the question is less earth shattering but still important: why does ice form at the top of a pond and not at the bottom?
Water has a strange property. If you have a thermometer at the top of a beaker of water, and another at the bottom, and then slowly cool the water from room temperature, around 20ºC, the coldest water is at the bottom to start with. But at 4ºC, cold and hot are at the same density, and then as the temperature drops further, the cold water, sub 4ºC, is now lighter and rises to the top. And so freezing takes place there, and not at the bottom.
It’s a fortunate property of water, as imagine if ice formed on the bottom first: life at the bottom would have a very hard time of it in the ice, and any fish would be forced upwards by the growing ice; easy victims to predators in a long winter.
Cold can be devastating to some plants. Just think of lettuce put in the freezer. It becomes limp and unappetising, and doesn’t recover when taken out of the freezer. It’s due to the high proportion of water in the lettuce leaves, which become ice crystals. When the lettuce is defrosted the cell structure breaks down, leaving a gloopy mass.
A few days ago, I came into the garden, and the acanthus near the back stage was suffering in the cold. The massive leaves were wilting in the sub zero temperatures. I wondered if they would recover. Today, they don’t look so unhappy, so maybe they will. I shall keep an eye on them.
The daffodils by our middle stage are fine. These, though, are native plants, used to our winters. They have evolved to stand them. The succulents in the raised bed are all fine and cheerful. They have no fear of the cold, growing in desert areas where the nights can drop below zero. We have several yuccas at the rear of the garden. They look so tropical, you would think they would hate this chill, but I see no signs of suffering. They have tough, long spear-like leaves, which have developed to conserve water in the desert environment they come from. And like the succulents, they have evolved to stand cold nights, and so our winter.
Birds are not so fortunate. They are warm blooded and must eat a lot in this cold weather to maintain their body temperature. But the ground is frozen, so they can’t get to insects and worms in the earth. It’s why bird feeders are essential for their survival in this cold weather.
There are many sparrows flocking around the feeders under the front cherry tree. A favourite haunt is the nearby privet, evergreen, giving them a little shelter from the bitter winds.
In my last blogs, I have written of my efforts to replace cow’s milk in my diet. The reason being that cows give off copious methane, a dreadful greenhouse gas, and male calves of milkers are slaughtered at birth. Having tried various milk replacements, and still not quite happy, I made some peanut milk. It’s cheap, easy to make but I don’t like its taste in tea, it’s just about bearable in coffee, and makes a decent banana milkshake. Not good enough. So, I am still on the lookout for the perfect replacement.