Tropical Temperatures in Wales

The garden has been in a state of suspended animation over the last week. Influenced by the high pressure which has dominated recent weather patterns, we have had gloriously sunny days, no rain and hard frosts at night. Good for outside jobs like replenishing wood stocks after a hard winter, but pretty hopeless for plant development. So why the ‘tropical temperatures’ at the head of this post? Well, having mentioned subtle temperature changes within flowers in my first blog post about crocus flowers, I thought I’d say a bit more about how I measure local temperatures in the garden. I do this in case anyone else wants to explore this fascinating aspect of microclimate around their own garden. About 10 years ago I bought the pictured battery-powered digital laser thermometer (from Maplins, I think). It’s proved robust and efficient and I’ve used it around the garden, in the house to check for cold spots, and also out of interest on our wood burning stoves, flue and chimneys. I don’t know the exact science, but it gives reasonably accurate readings over a wide range of temperatures, by pointing the tiny red laser dot it emits, onto the object you wish to measure the surface temperature of.

Laser digital thermometer

So after clocking the outside temperature at minus 7.0 degrees C first thing this morning behind our house, I waited until about 11.15 am, and then went to the lower section of our copse garden to take a few readings. We’d had sunshine since sunrise, but the air temperature was still quite chilly. You can obviously get a rough idea of what this is by pointing the laser dot at a leaf in the shade – in the next photo I used a small-flowered rhododendron just budding up.

You can see the reading is about what I would have expected at 0.0 degrees C.

Shaded leaf/air temperature about 30 cm above ground at 11.15 am


However the next image might surprise you. It certainly did me. Turning the thermometer to point at a moss-covered area of ground barely 70 cm from this first reading, between groups of Crocus flowers, you can see the tropical reading of 38 degrees C! You must remember that our garden is 800 feet up in the hills of Wales, and it’s the first week in March. Quite extraordinary, but of course it is a fairly steep, south facing slope, and my guess is that the moss covering also traps a fair amount of air within it, which is acting as a sort of green duvet.

Ground temperature of 38 degrees C in Wales at 800 feet on March 7th

This has a big significance for what is growing on these southerly slopes at this time of the year. Many Crocus species originate from much warmer climates than ours, but by planting them where they can make the most of available spring sunshine you can clearly make them feel as though they were back home, and as I mentioned in the last post, it’s not a bad strategy to have your ovary and developing seeds located just below the ground, where although temperatures won’t be as high as this, will still probably aid seed development.

Following on from this theme, I’d already noticed how seed germination and leaf growth had started really well in lots of area of moss-covered copse ground where seed had naturally fallen, but that in my carefully cultivated tilth with a similar angle, and in a raised tyre for extra warmth and drainage but facing east, not a single leaf was showing.

Lots of seedling Crocus tomassinianus – to the left of the oak leaf

But look how much lower the temperature is here, even though this picture was taken about 40 minutes later when the sun was higher in the sky.

Hairy Pulsatilla vulgaris leaves and shoots


Finally, with these very cold night time temperatures of late, I’ve worried that the early shoots of many plants in our copse may suffer, and was then struck by how many of those growing away vigorously have really hairy leaves and shoots, the most obvious being the Meconopsis grandis, and Pulsatilla vulgaris. I had to include the photo of the Hepatica nobilis as well, because although the leaves aren’t hairy, and the flower stems are slightly hairy, they are such pretty flowers, in whites, pink and blue. Sadly though, my idea that this hairy coating might help heat retention wasn’t borne out by readings from my thermometer, when last night, at 9pm they were all registering minus 4.5 degrees C. Just the same as the surrounding fallen leaves. Ah well.

Hepatica nobilis

Hairy Meconopsis grandis emerging leaves

Finally, last week I photographed for the first time what seemed to be a worker honeybee, systematically visiting Crocus flowers in the garden. We don’t have a hive, and only very rarely in the past have we seen honeybees in the garden, and never this early in the year, although we do have huge numbers of bumblebees. What was interesting was that unlike the bumblebees, and the bee shown in my last post, this bee showed no interest in the base of the flower. Rather it methodically worked the open blooms, and was clearly carefully collecting pollen grains, onto its rear leg pollen baskets, but instead of probing the flower base appeared to be licking or chewing the frilly stigma of the Crocus, before flying on.

First worker bee ever seen on a Crocus flower in our garden