Monday, February 4, 2019

My Year of Orchids: Water balance in epiphytes

It’s pouring rain outside but I’m not worried that my orchids will drown. Nor will any of my other epiphytes- tillandsias, bromeliads, or cacti. You can’t overwater an epiphyte.

Well I should modify that statement. An epiphyte living in the tree canopy in natural conditions can’t be overwatered. Plants in pots are another question. But I’m talking about orchids in a natural or neatly natural state.

Orchids in nature take in the water they need and no more. Water enters mostly through their roots, of which there are several kinds with lots of different roles-anchoring, exploring, etc. Once a root has absorbed its portion of water it stops. It can do no more. Some water is absorbed through the leaves and stem but these amounts are negligible. Mostly the orchid body, including the roots, is built to conserve water. Not to take in or let out too much.

Orchid metabolism is a further and very significant factor in water conservation. Since water vapor is lost through stomata (leaf pores) during photosynthesis the orchid does most of its photosynthetic activity after dark, when the ambient humidity of the air is higher. This way less water is lost from the orchid body. And sugars manufactured during sunlight hours are reconfigured to fuel energy-producing activities.

Orchids aren’t the only plants that do this. But they do live in some of the wettest environments. Which brings us back to the question. If they’re already living in a humid environment why conserve water so carefully? The answer is in their epiphyte lifestyle. Without a soil substrate where they can find water molecules during dry times the orchids are totally at the mercy of their immediate environment. Better to conserve water than to waste it.

If you’ve taken the time to feel your orchid’s leaves you’ll notice that they’re rubbery or leathery or otherwise thick and toughened. Something like a cactus. This kind of succulence is an anatomical feature that conserves water. So orchids are equipped in many ways, anatomically, metabolically, and structurally to conserve water and exert control over their immediate environment.

We still haven’t discussed why you can’t drown an orchid but doesn’t it make sense? If there’s no standing water-just a cascade of rain, and if there’s any kind of breeze, the orchid plant limits its intake and perhaps more important, retains plenty of contact with ambient oxygen. Unlike greenhouse or potted plants that are susceptible to molds and fungi, insect pests, and other pathogens, the outside orchid, which evolved to live in the open, has natural defenses that protect it.

As I continue to work with and observe my orchid garden I feel myself becoming more and more a champion of natural conditions (at least when it’s possible) for growing these fascinating plants.

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