This week winter may return to the Loudoun Valley. It was almost 70 degrees here this afternoon, but the National Weather Service is forecasting lows in the mid-twenties Monday night and Tuesday night, and then again on Friday and Saturday. So the other day we put the strawberries back to bed. Many of those plants already have flowers on them, but we hope these row covers will trap enough heat from the soil to keep those flowers from freezing.
Temperatures that low are not unusual in early April, says Tony Wolf of the Virginia Cooperative Extension; the unusual temperatures were the ones we had in March, with historical rankings in the top ten warmest at many locations, and average temperatures nearly seven degrees about normal. In other words, March was like an average April, so sap started flowing and blossoms came out a lot earlier than usual in our orchard and our vineyard -- and you can't put blankets on the trees. "Plant development stage will determine how much frost damage may occur," Wolf says, "with variations according to wind speed, cloud cover, and humidity."
"The wind and sky conditions for the morning of 6 April indicate the strong potential for a primarily radiational cooling event – clear skies with winds abating after 1:00 am and calm the rest of the morning," Wolf says. "It is under these conditions that strong temperature gradients can develop as a function of altitude (or elevation), with coldest air temperatures found at ground level and warming temperatures aloft, up to a certain altitude (or elevation), above which the air temperature decreases again with increased altitude. Solid-set wind-machines and helicopters are useful under such radiational cooling conditions because they displace the colder air at the surface with warmer air created with the temperature inversion."
Here's hoping that cold air near the surface doesn't dawdle.
Unlike peaches and apricots, spinach and kale love frigid nights, so we expect to have them available as a you-pick bonus through the end of the week.
Member bonus: one clear bag. Additional bags at $4.99 per pound.