Since the microclimate around our house has temperatures similar to those at South Lake Tahoe, we are more likely to freeze than Carson City or Minden. Cold air is trapped on our property. At this time of year, I pay attention to the weather or lose my plants. I check the weather report every evening. I look at the sky after the sun goes down to see if it is clear. I assess the wind. A clear calm night often indicates a freeze, particularly in autumn. I’m keeping the plant covers handy.
A microclimate is the climate of a small area that is different than the area around it. It may be warmer or colder, wetter or drier, or more or less prone to frosts (Cornell University). A microclimate may be a large area such as Washoe Valley, where we live, or it may be as a small as the north or south side of a house, a courtyard, or an area next to a building. Elevation, vegetation, proximity to water, exposure to sun or wind, or protection of trees, fences or boulders create and influence microclimates. Buildings, concrete and the asphalt of a city can warm an area. Fruit tree blossoms located on a slope often survive a late spring freeze, while those at the bottom of a valley may lose their flowers and produce no fruit.
The average first frost ranges from Sept. 15 to Oct. 1 and the average last frost ranges from May 1 to May 15. However, the microclimate around a home may make those dates inaccurate. Our yard generally has a freeze around the first week in June and again in early September. Successful gardeners know their microclimates.
Good gardeners also pay attention to frosts (32-36 degrees), light freezes (28-31 degrees), moderate freezes (24-28 degrees) or severe freezes (below 24 degrees). Tender plants such as tomatoes, peppers and cucumbers may be damaged during a frost, depending on its duration. Most of the non-cold hardy plants in the garden die with a freeze, even a light freeze. However, a safe time to prune evergreens such as pines is after a severe freeze when bark beetles and borer insects are done for the season.
Covering plants gives two to five degrees of protection. Covers that don’t touch the plant give better protection. Woven fabrics are better than plastics or paper. The extra work of covering plants may buy you a few more weeks of harvest.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.
