Our first frost came about one week earlier than the last few years, here in the mid-Willamette Valley. I walked through my gardens at around 7:30 this morning, and I noted frost only on the the main lawn, and temperatures in the 40’s. This really illustrated the concept of a micro-climate. What is a micro-climate? This is a term we use to describe an area that, due to geography (hills, valleys, near a lake, near a house, etc), differs in climate (high and low temperatures in particular) compared to the greater surrounding area. If you live in a micro-climate, you might watch the news & weather for your region, and find that the low predicted temperatures do not correlate with what you are seeing at your home. This is especially common in Oregon, where hills, valleys, and mountains can change weather dramatically within just a few miles. A smaller version of a micro-climate would be a garden bed next to your home, where it will be kept slightly warmer than other areas due to the radiant heat from your house, and perhaps have longer protection from frost. In my yard this morning, the exposed large lawn had frost, while areas more sheltered by vegetation seemed spared. It is important to be aware of your average first frost—tender annuals such as flowers and vegetables are often killed by frost (especially a “hard frost”). If you want to extend their lives, you need to anticipate frost and cover things the previous night. A good predictor of frost in the Willamette Valley are clear nights starting in mid to late September or early October. Cloud cover actually keeps our ground warmer. Today, our frost was what I would call a light frost, and most plants would survive it.
Posted in Gardening