We have lots of perennial plants in bloom at the nursery, and their foliage and flowers could be severely damaged by those temperatures. We also have many, many crops that we would have moved outside by now - all our gallon perennials except the tenderest, like salvias and hebes. We normally would have our 4" perennials in the field by now, or have their moving well underway.
Because of the record cold temperatures we have experienced in the past few years, we grew our 4" perennials in a different manner this year. Usually, we sow them in 288 cells from July to October, depending on seedling size and vigor, and then plant them to their finished containers in unheated houses in November. This year, we sowed them in 105 cells - a substantially larger unit - and kept them in houses that could be heated if necessary until after the first of the year. All were planted in their final containers in January and early February, and there was room to put them back in houses that could be heated. Our customers' advertising schedules are the drivers here - not the needs of consumers.
Many perennials that are in unheated houses are at risk from the coming cold temperatures. We have covered them with a non-woven frost protection cloth, which will stay in place until the weather changes. They are growing in an unheated coldframe - usually perfect for winter protection of perennials, and spring production of cold-conditioned annuals. 18 degrees would be nothing at all in many parts of the United States - it's 10 degrees in Spokane as I write - but the demand for marginally hardy plants in the Pacific Northwest has influence what we grow. And, we need to have really good perennials early in the season to keep our place in the market.
Here are some steel hoop houses that have 2x4 lumber crutches in place t0 reinforce their bows and ridge. All of our steel houses have had some damage in the past from snow load - of course, they are inexpensive structures that would have no utility whatsoever in harsher climates.
When we had our crazy snowstorm a few years ago, with 16" of snow over several days, we actually removed the polyethylene from most of our unheated greenhouses. We ended up cutting the polyethylene from 13 coldframes to save the structures. It was not extremely cold during that weather event, and all that snow was a great insulator for the crop. There is actually a nursery in the Skagit Valley that owns a snow-making machine - the kind that ski resorts use to supplement low snowfalls - that they use to cover their crops with snow in advance of Arctic air masses and low temperatures.
Guys have come into work today to help with snow removal. These unheated houses can easily carry the snow that is on them now, but we are concerned about the possibility of more accumulation. We've had situations in the past where a few inches of snow were on greenhouses roofs, and then freezing rain occurred. The snow on the roofs took up the water like a giant sponge, multiplying the weight, and then more snow fell. Nasty! That was the first year we ever cut poly to save greenhouses.
Only Chi and all the little kids that get to stay home from school really like snow here in western Oregon. For nursery operators, it means many hours of cold, wet work. And the 18 degrees? Months and months of careful cultivation can be destroyed over night. With all our precautions, temperatures in the unheated houses, under the thermal blankets, should go no lower than 25 degrees, and we will probably have modest damage to our crops if any.
Let's just hope that we'll have a beautiful spring this year, and that it starts next week!