Botanist Visiting London--in December

Two years ago I was in London in the first half of December. Looking back at the photos, I'm struck by the contrast to Colorado at the same time of year.

London, December

northern Colorado, December

London is well north of Denver, any map will show you that. Yet, the ocean effects prevail: it was much warmer than the Colorado we'd left behind. Not only was it warmer, I saw many plants that we cannot grow in Colorado.


For example, European holly, Ilex aquifolia. (link) There were huge beautiful trees in London. It doesn't survive in Colorado.

Big European holly tree, Ilex aquifolia, London, December

Another lovely plant in London but not Colorado is the camellia (Camellia spp. link). Colorado is much too cold for camellias.

Camellia (Camellia sp.) with a flower, London, December

I don't want to say it was warm in London in December. The air was chilly and when it drizzled it was hard to bundle up enough.

But, look at the flowers:

Carnations; something had knocked them over but
not interfered with flowering. London, December

Nasturtium, London, December

Cyclamen, London, December

Carnations (Dianthus caryophyllus) are somewhat cold tolerant but the least frost will kill nasturtiums (Trophaeolum spp. link) and cyclamen (Cyclamen spp.). And that's a key to this contrast. Cold temperatures that are above freezing slow plant growth and will eventually kill many warm-weather plants. But freezing is something else entirely. Water turns to ice at 0 C/ 32 F. From a liquid to a solid. Not only that, it expands. Plants not adapted to frost have their cells torn up as the water in them suddenly takes up more space than before. That is the chief cause of plant death after a frost. Most liquids don't expand when they become solid. Water is wonderful in many ways, but if we ran life on some other liquid, the freezing point would be a less drastic biological limitation.

Of course, below freezing, the liquid in plants is a solid and won't flow up or down at all. So no biological activity is possible. Plants that survive where water freezes have insulated their roots well underground and/or incorporated"antifreeze" molecules. And of course reinforced their tissues against the mechanical damage of freezing.

The list of plants that "grow in London/ don't grow in Colorado" indicates that frost is rare in London. You can't grow a big camellia where there are severe freezes. If there had been a frost before I got there, I wouldn't have seen nasturtium or cyclamen flowers. Primarily, the ocean keeps London mild. With currents coming from the tropics (link), the Atlantic stays above freezing. The water shares heat with the land, most of the time keeping the land from freezing.

Probably, also, the area that is London freezes less often that in did when it was a small Roman town, because humans leak heat. We give off heat from our bodies and from our energy-burning activities from driving to cooking, and especially, heating buildings in order to live in pleasant temperatures. My area does not have 8 million people releasing heat.

Some of London's big trees had lost their leaves of course:

Along the Thames, London, December

But in Colorado, all of them had. And the grass in Colorado was yellow where not snow-covered. (photos at top, bottom of this post). My London photos are full of green leaves.

One London-in-December experience that my photos don't show is the day length. London was dark until 8 am and again before 4 pm. That reflected how far north we were. The days never get quite that short in northern Colorado.

One more contrast:

Citrus (grapefruit) at Chelsea Botanic Garden (see the green fruits?). Ok, they're proud to have the northernmost grapefruit tree. But good grief, not only can't Colorado grow any citrus, this one has green leaves in December.

Citrus, Chelsea Botanic Garden, London, December

Landscape, Larimer County, Colorado, December

There's a lot more than latitude to the climate that determines plant abundance. The difference between London and northern Colorado is driven by the fact that large bodies of water hold heat longer than large areas of land, so oceans moderate the temperature of coastal cities. Or conversely, midcontinent regions experience much more change in temperature, daily and seasonally, than coastal areas.

If you live in the middle of a continent, check out the coasts some winter. And vice versa.

Questions and comments welcome.

Kathy Keeler, A Wandering Botanist

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