I grew up on the East Coast, and if you’ve ever spent any time there — or of course, in the South — you’re familiar with the term “it’s not the heat, it’s the humidity”. We got a tiny taste of that weather this week in Northern California as a moist airmass moved over us, bringing clouds, thunderstorms, and sticky damp heat. It makes for a nice sunrise over the farm, but not much else good. .
The majority of the most common summer vegetables and fruit grown and eaten in the U.S. are native to places with dry, warm weather — so called “Mediterranean climates”: Italy, Greece, Spain, Mexico and Peru, and the Middle East. I could list them all, but it’s much easier to list the ones that enjoy humidity. Sweet Potatoes, for example, are originally from Africa. That’s about it.
Our supermarkets are full of tropical fruit adapted to hot and wet areas: bananas, mangos, papayas, pineapples, etc. But most of these are extremely sensitive to cold weather, and since they are almost all trees, cannot survive winter in most parts of the U.S.. Others will not flower or make fruit in places where the length of day changes over the course of the year. The only tropical fruit species that is commonly grown in the U.S. is citrus, and even then only in a few states.
Due to their genetic propensity towards dry weather, tomatoes, melons, beans, cucumbers, zucchini as well peaches, figs, grapes, plums and apricots all share a common trait: a lack of tolerance for wet weather and high humidity. Powdery Mildew is a common fungus that is spread by heavy dew; Late Blight, Brown Rot and Fire Blight are triggered by heavy rains. In an ideal situation, most of these summer crops prefer access to water through their roots but have their leaves and fruit stay dry. Put a different way: they grow best in a dry climate with irrigation.
There is a deeply held and persistent belief among urbanites that there is something bad about farming in dry areas, and that irrigation is profoundly unnatural. This belies a profound lack of understanding of geography, agriculture and history. The best soil for farming is usually located alongside rivers, often in valleys below mountains with extensive drainages. The Hopi practiced irrigation for thousands of years sustainably. The Aztec, Maya, Egyptian, Roman and other ancient civilizations grew all their food in a dry climate using irrigation. This is why so many of the foods that we eat grow so well in California.
After one of the driest winters on record in California, we have been having an unusually humid summer in the Central Valley, owing to an abnormal weather pattern. Most summer days here proceed from sunrise to sunset without a single cloud in the sky; this year we have had numerous days where we don’t see the sun until afternoon or when clouds have dotted the sky all day.
Clouds = humidity = plant diseases and we have had those in abundance this year. It’s really hard to imagine trying to farm the crops we grow in someplace like Georgia, Virginia or upstate New York, where the driest days in the summer are twice as humid as anything we see.
Sure it’s hot in the Central Valley. But most of the time, relief is as close as the nearest shade, or at worst, nightfall. The sun is the source of the heat, and when it goes away the temperature drops. I’ll take it any time over a day like Tuesday, when you couldn’t even sit under a tree without breaking a sweat. And so will the summer crops.