This roller coaster of weather also makes the protection of plants in our container farm a rather dynamic process. In order to keep our plants from either experiencing too much cold or warmth, we must alter the environment they are in. We employ five different methods of overwintering, each one has their specific process for handling the fluctuations in temperatures. Below is a list of each and how we address them throughout the winter:
1. Lay over and hay: This method is utilized for specific deciduous plants that do not have much of an issue with leaf retention or hairy stems. We allow them to go completely dormant, knock off any remaining leaves, lay them over, cover them with plastic, and lastly with an 8" -12" layer of hay. These plants will remain under the above material until about mid-March, when the very cold days of winter are typically over. Because of the level of insulation, there is minimal temperature fluctuations making the threat of them prematurely breaking dormancy fairly unlikely.
2. Minihut: These are small houses constructed out of bent ¾" PVC, covered with a layer of white plastic and held down with sand filled tubes. This method is used for 1 gallon containers. With these, we typically will completely uncover them when the temperatures are going to be above freezing for a solid week. This allows them to air out some and we typically irrigate them at this point to flush out any salts and ensure they are well hydrated for the next round of cold.
3. MiniHouse: We erect these 6' metal structures each year over deciduous material that typically has a leaf retention problem (Itea) or fuzzy stems (Perovskia), but can also tolerate more rapid changes in temperatures due to it being a smaller structure (unlike Buddleia which would have significant winter loss in a minihouse). Once up, these are covered with a white plastic film and secured to the ground using a system of 2x4 boards and rebar. A week of above freezing temperatures warrant tying open each end of the structure. For longer periods of warm weather, we will completely uncover the structure and irrigate where necessary.
4. Hoop Houses: This is the signature of the nursery as people pass by on I-35. Being large, permanent structures, they really jump out. Covered in a white plastic film and secured with lath and staples, these structures house our broadleaf evergreens and more "finicky" plants that don't like large, frequent swings in temperature. Because they are so much larger inside, the temperature change is much slower than minihouses and is more easily regulated by opening the doors on the end when the daytime temperatures are above 30 or it is sunny.
5. Open Air Overwintering: For almost all of our needled evergreens, we overwinter them in jammed beds lined with containers filled with potting media. The containers around the edge are strictly for insulation and will have the material in them reused. We really don't respond to temperature swings with these plants aside from irrigating them the soil is thawed.
The weather forecasts are very important to us throughout the winter. By staying on top of temperature changes and responding to them appropriately, we allow our plants to stay healthy and ready to leap into action once the warmth of spring arrives.