For six months of most years, California is a very dry place. Sometimes our climate is called “Mediterrean”, but that’s a misnomer because many places adjacent to that body of water actually get regular summer rainfall. In the Golden State outside of the mountains, we get an average of close to zero.
So how can it be that California produces more agricultural bounty than any other state in the U.S. ? As so many people ask during our droughts, “Why are we farming in a desert when it rains so much more in other places?”
Most of the food crops that are grown in the U.S. during the summer are actually native to places like California — not actual deserts nor Mediterrean areas, but places with distinct wet and dry seasons. Those crops — Corn, beans, tomatoes, melons, squash, cucumbers, peaches, almonds and pistachios — don’t like getting rained on. Some of them don’t mind getting their leaves wet when the plants are small or when their fruit is immature, but others are generally intolerant of any rainfall whatsoever.
Surface moisture on leaves and fruit causes a wide spectrum of plant diseases, both fungal and bacterial. Flooding of the soil causes fungal diseases that affect roots. Farmers who grow the summer crops I listed above in places that get regular summer rainfall and very hot weather use huge amounts of fungicides simply because they have to. Farming those crops organically in the South or parts of the Midwest is essentially impossible.
Summer rain and humidity also make it difficult to control weeds organically.
The lack of summer rain in California also usually translates into much lower humidity even — especially — in the hottest parts of the state. That is also good news for organic farmers, because there are numerous warm-weather plant diseases that don’t need rain but that thrive in higher humidity. We might get short periods — most often in the spring but sometimes in fall — where we see those problems spring up. But they rarely pose a severe threat.
One of the best known examples of a warm-weather, humidity-driven plant disease is the organism that caused the Irish Potato Famine. Phtyopthora Infestans, or “Late Blight” is a water mold that can also infest and kill Tomato plants. Late Blight is a common disease for organic growers in many parts of the U.S., but is extremely rare in California.
Our bone-dry California summers simply better for growing crops — organically or otherwise. Normally, most of the heat in the summer here comes directly from the sun. Once it sets, the dry air cools off relatively quickly and continues to cool overnight. At sunrise, it is usually no warmer than 60 degrees. It serves to chill the produce growing in the field and keep it fresher for the next day’s harvest. It also tends to temper the growth of the crops, keeping our work relatively manageable.
Speaking of work, cool mornings also make for pleasant conditions to start the day. This might surprise coastal dwellers in CA who recoil in horror when they encounter the hot, dry air of the Central Valley. But when we start at sunrise, the temperature here is often the same as it is in Berkeley or San Francisco. And we finish work at 2:30, which is usually several hours before the heat peaks. My in-laws from Texas, where it is just as hot as the Central Valley but much more humid, come here to the farm in the summer to escape.
This week, however, we’ve had an unwelcome visitor arrive in Northern California: the humid, wet and stormy remainders of a Tropical Storms from south of Baja. Its visit happened to coincide with a fairly routine heatwave, which means we are dealing with hundred-degree temperatures as well as high humidity and unusually warm nights. Since Monday, it’s been muggy, cloudy, hot and humid. We’ve had thunder and a little rain. Unfortunately, there’s also been lightning and now there are several fires burning in Norcal. That means we could end up with nasty, smokey air as well. And the humidity is expected not just to stick around, but to increase next week.
We are not acclimated for this Southern-style weather, nor are we experienced or equipped to deal with the potential plant diseases it might bring with it. Since 2020, August and September have thrown all kinds of new challenges at us and we haven’t always been able to manage them. Wish us luck!