Auxins, tropisms and apical dominance: The curious case of the crooked conifer

Cook Island pines grow straight up in the New Caledonia islands. But anywhere else, they grow toward the equator.

View of Piscine Naturelle D'Oro (natural pool) in New Caledonia

Here we are, the last week of August. The summer season is coming to an end, the kids are going back to school, our veggie beds and flower containers are winding down —although my overwintered geraniums seem to be just reaching their stride — and our lawns are parched — unless like me you are willing to spend your children’s inheritance to water it).

That is all about to change, which I will delve into next week in great detail as we explore all the wonderful planting options for fall containers and cool-season veggies. But, for now, I want to explore something both frustrating and amazing in the plant world.

In my front landscape, I planted a Blue Surprise Lawson cypress a couple of years ago, with the image in mind of a strong vertical accent. Blue Surprise is a beautiful, fine-textured evergreen whose needles are not unsurprisingly a lovely shade of blue. This is a plant that normally grows bolt-upright, as in straight as an arrow. But in my yard, it is listing strongly to the west as if someone or something is pushing it in that direction. In fact, what is happening is that it is growing toward the light of the afternoon sun, but more important perhaps, it is trying to get away from a towering white pine growing to the right and slightly above it. It’s as if it is running from big brother.

Of course, plants do naturally grow in different directions; some are very upright while others grow horizontally. Our native conifers, with their strong central leaders, are usually tall and narrow while our native big-leaf maple is broad and round. That kind of growth habit is caused by something called apical dominance. But the action of plants, like sunflowers, that wake up in the morning facing east and go to bed 180 degrees to the west is caused by various hormones called auxins that respond to the light. Movements of plants in this way are referred to as tropisms. Generally speaking, we categorize them into geotropism, phototropism and hydrotropism.

In the case of my Blue Surprise, my left brain is telling me this is simply a phototropism response, while my right brain likes to imagine it’s a relational response and that Blue just wants to get the heck away from the controlling influence of white. I find that scenario much more interesting.

Now, for a really whacky case of “crooked conifer syndrome” — CCS is not a real syndrome, I just made that up — one needs to travel to the New Caledonia islands and observe the Cook Island pine, which is not a pine at all (stupid common names) but a conifer related to the more familiar monkey puzzle tree that we see growing here in the Northwest.

Cook Island pines, in their native habitat, grow straight up, reaching 200 feet tall and only 15 to 20 feet wide. But move them away from the equator and they will grow at a 7 to 8-degree angle, always back in the direction of the equator. No matter how tall they grow, they will continue to lean toward the equator. Scientists don’t seem to be 100% sure of the cause but believe it may be a combination of sunlight, gravity and the Earth’s magnetic field pulling or pushing them in that direction.

Again, the left brain in me thinks this sounds reasonable while the right brain is leaning toward the thought that they are just home sick. Either way, it is a very curious sight to behold.

Plants are amazing creations that, while we may find it hard to believe that they are actually sentient, are clearly capable of performing tasks that seemingly require some level of cognition. Whatever you believe, don’t short change the plant world. After all, we would be up a creek without them.

Free class

The next free gardening class at Sunnyside Nursery in Marysville will be “Refresh Your Lawn” at 10 a.m. Sept. 9. For more information, go to www.sunnysidenursery.net/classes.

Steve Smith represents Sunnyside Nursery in Marysville and can be reached at sunnysidenursery@msn.com.

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