How does fog affect your plants? Let’s find out.
First, what is fog?
Fog is the low-flying equivalent of stratus clouds. It contains tiny droplets of water and ice crystals that have formed through condensation. This condensation occurs when the difference between air temperature and the dew point is less than 4.5°F (2.5°C). Dew point is the temperature that ambient air must reach to become saturated with water. When that point is reached, water particles start collecting around any dust, ice, pollen, or salt in the air.
Unlike mist, which we can see through, fog tends to be harder to see through. Technically, fog reduces visibility to less than 0.62 miles, but who’s counting? There are several different types of fog, but I’ll leave that to you to explore. Let’s find out what all this moisture in the air does to our garden plants.
Fog diffuses sunlight, much the way smoke from fires does. [See Yellow Sky Days] Instead of simply shining downward, light particles get bounced around, allowing photosynthesis to occur in places where it normally might not. Of course, if there’s too much fog, photosynthesis is significantly reduced.
Periods of fog often cause discoloration, stunting, and even wilting in crops such as wheat. These responses are temporary and they often disappear once the sky clears.
Extended periods of moisture often increase the likelihood of disease. Bacterial head rot, black scurf, black spot, cucurbit scab, russeting, sooty blotch and flyspeck, and tomato gray wall are more likely in areas with frequent fog.
Foggy days are a good time to apply insecticidal soaps to manage cabbage aphids and other pests. And dormant oils are best applied just after a period of fog. Fog reduces topsoil drying, acts as a protective blanket during cold weather, and slows evapotranspiration, reducing the need for irrigation.
If you’ve never heard Eddie Izzard’s hysterical description of fog, check out his Dressed to Kill video. It cracks me up every time.
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