Dear Tom –
I recall several on-line conversations last winter about protecting coldframes for winter weather. What steps do you suggest? Thanks.
— Sarah from Asheville
Dear Sarah –
This is a good time of year to be finishing up coldframe preparations but our preparations start with the yearly seed order. If we go to all the trouble to build a coldframe, we try to be sure that it is overflowing with good food through the winter. A great source for what to grow in your winter coldframe is Eliot Coleman’s Winter Harvest Handbook (Chelsea Green 2009). For which varieties to plant, I often use Johnny’s Selected Seeds snowflake icon. Early on we tried planting all the greens with a snowflake to see what worked for us. That experiment led to our winter salad mix with Claytonia as a leading component.
Timing of the winter crop is important too. As the days become shorter, cooler, and grayer, plants have less energy for growth. Coleman offers a goal of growing plants to a mature size before days are less than 10 hours long. For Asheville that short day period is roughly from Thanksgiving to mid-January. It also makes sense to plan for the crops that will follow your fall-planted crops so that your transplants are ready as the winter crops are harvested. With the major investment in the coldframe structure, we hate to see it ever empty.
Steve Moore at the NCSU Center for Environmental Farming Systems gives a great talk on the benefits of double layers of protection for coldframe productivity. Most folks use row cover over hoops inside the coldframe for this second layer but Steve prefers used greenhouse plastic as the second inner layer. A word of caution – row cover breathes and but plastic does not so be sure and pull the plastic off on sunny days if you go that route. He hosted an August webinar on season extension, which may be in the CEFS archives if you want more detail on his research.
Hoops are important to support inner row cover. On cold nights the fabric freezes and will scorch the crop wherever it touches. We use the largest high tensile wire we can get at Southern States. Often the roll of wire is just the right diameter so we cut through the roll in one place and the hoops are ready. We use a hoop about every 5 feet and offset the hoops in adjoining beds. Inside the coldframe wind is rarely a problem but we usually put weights on one side to make handling the fabric easier. The October Growing for Market has a clever system for managing fabric using cables instead of hoops if you are feeling innovative. . Another alternative is fiberglass rods that bend over the bed. I believe Reems Creek nursery has them.
Be sure and winterize your irrigation system before temperatures get into the 20s. Hoses will thaw out eventually but it can be several frustrating weeks. PVC pipes usually rupture when the water in them freezes. Putting a drain at the low point of your system and allowing air to enter at the high point will usually work if your supply line has no dips. A frost-proof hose bib and supply lines below 2 feet will simplify winter irrigation.
Finally getting back to your comment about protecting the frame from snow load, here are a few tips from our experience last winter and conversations with other growers:
- A gothic shaped coldframe sheds snow better than quonset shaped houses
- Four-foot hoop spacing is stronger than six feet or more.
- Avoid drilling into hoops – use clamp-style brackets instead – to avoid weakening the frame
- Be sure your house is anchored to the ground to avoid liftoff in high wind
- Brace your end walls outward to avoid snow load pulling both ends toward the center.
- Have portable heaters ready to melt a layer of snow under the snowpack for easier removal
- Use center posts sized 4X4 or greater to provide added snow load resistance.
- Place a rigid pad under posts to avoid the snow load driving them into moist soil
- Have extra brooms and a list of phone numbers handy just in case.
- Be cautious if the snow gets ahead of you. Coldframes can collapse suddenly when their snow load is exceeded.
To avoid ending on that not very cheerful note, NOAA predicts a warmer than average winter with average precipitation.
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Author: Tom Elmore
Tom Elmore is co-owner and operator of Thatchmore Farm in Leicester NC. He has grown certified organic fruits and vegetables for 25 years and serves on the Boards of the NC Greenhouse Vegetable Growers Association and the Organic Growers School.