A cold frame is used to harden seedlings before planting them in the gardens. “Hardening” means getting the plants accustomed to the wind and direct sunlight.
Instructions for Building a Cold Frame
- Determine the length and width needed to house all the flats of seedlings that will be moved into the cold frame. We will call that area Dimension A
- Determine the length and width needed to house the flats of plants including width of the hay bales that will be surrounding Dimension A. We will call that area Dimension B
- Cover Dimension B with ground cloth and use landscaping pins to hold the ground cloth in place.
- Lay straw bales closely together along the outside edge of the dimension A. Straw bales can be purchased from any farm or feed store, i.e. Corrales Village Merchantile.
- If you replace all of the straw bales at once, haul the straw bales using the S2N trailer. A pickup truck will be too small to haul a full load. Each year, we generally replace any straw bale that is falling apart or that is significantly smaller in height. Height is important because the cold frame must be deep enough so it doesn’t interfere with plant growth.
- Use boards across the top of the cold frame to support the covering
- Cover the top of the cold frame with a sheet of Agribon Ag-15 row cover to provide shade and to protect the seedlings from beet leaf hoppers. If one sheet of Agribon is too narrow to completely cover the cold frame, sew two pieces together along the long edge. Use a sewing machine instead of hand stitching so the seam is strong and use a medium sewing machine stitch. Spread the Agribon cover over the straw bales and pin it in place with landscaping pins.
- Place shade cloth over the top of the row cover and duct tape it to a 2” PVC pipe leaving at least 1’ of pipe extending beyond each end. That will allow the shade cloth to be rolled up when opening the cold frame.
- Unroll the row cover and shade cloth and use landscape pins to secure it to the straw bales on the far side. The pins in the far side will remain permanently in place.
- Once seedlings are moved into the cold frame, monitor the temperature at least twice each day – early morning and around noon. If the temperature gets too warm, immediate steps must be taken to cool the seedlings, i.e., a shadier location or more ventilation.
- Also, monitor nighttime temperatures. If the temperature gets near freezing, the only options may be to add another layer of covering or to move the seedlings back into the greenhouse.
2023 Strategy
Our approach in 2023 will be to move the cold frame near the cottonwood trees along the south fence of the Sageser property to provide the cold frame with some light shade. There is a water spigot there but no electricity. It will be covered by row cover during the day to protect the seedlings from beet leafhoppers and by row cover and shade cloth at night to protect the plants from frost.
Once the seedlings have been moved into the cold frame they must be watered daily and gradually exposed to longer periods of sun. Check the temperature inside the cold frame at least once in the morning and once at mid-day to make sure the cold frame does not overheat during the day or get too cold at night.
