We have a dry and warming trend in the weather for the next several days. A west coast ridge of high pressure will build up, keeping our skies clear and helping to warm out temperatures well up into the 70s Friday, and into the low 80s through Monday. Things begin to cool next week, and we bring a slight chance of rain showers back to the area by Thursday of next week.
Yesterday I said objects can lose heat by conduction, but they can also lose heat by radiation. When this occurs, the energy passes from the ground directly into outer space, without (much) affecting the atmosphere. As a result, the ground can cool off to a temperature much colder than the surrounding air. So what does this mean when it comes to protecting tomatoes against the “Black Death?” Often, all it takes is a light tarp thrown over the top of them. And it doesn’t have to be a thick blanket… in fact the insulating properties of the covering usually won’t matter.
Here’s why: Assuming the frost is occurring on a clear night, all you have to do is block the radiational pathway from the plant to the sky in order for the tomato to keep from getting colder than the air. The thickness of the blanket doesn’t matter… just its opacity. Of course if the air temperature gets below freezing, you might be hosed no matter what you do.