Winter Farming Problems—It’s More than Frosty Fingers
Plants often die in the winter because ice crystals form in their cells. As water expands when frozen plant cells explode, causing permanent damage. Many plants, such as lettuce or swiss chard, can live through a few light frosts, but eventually the cell damage is too great and the leaves turn to mush. During our unseasonably cold December this year, with consecutive days of -15°F weather, we lost all but our hardiest crops.
Even in these kinds of extreme conditions, with proper selection at Joseph Decuis we can grow a variety of crops in our unheated hoop house. How do plants such as kale and spinach survive the winter?
Thinking Like a Plant
Plants store water and sugars (sucrose) in their roots during the warmer seasons. When colder weather hits, plants cycle this water and sugar through their leaf membranes. Water is a great insulator and the sucrose depresses the freezing point (think salt on a sidewalk). This combination helps protect the plants from freezing and permanent cell damage.
Plants do most of the work, so our job is simple: slow the process of freezing. Joseph Decuis’ hoop house is covered by two sheets of plastic with an insulative air pocket between layers. We use floating row covers just above the plants as an additional layer of protection. Each layer adds 3-5°F depending on conditions.
While these “blankets” add warmth, their primary purpose is to buy the plants time. In many ways, the floating row covers simulate snow, which acts as an insulator and protects crops from the harsh cold. Like snow, the covers slow the freezing process at night, allowing plants to move water and sugars from the ground to their leaves. In this way, we are simply allowing plants to be plants–we are not attempting to recreate summer.
In Greek mythology, Persephone, the goddess of vegetation, was abducted and forced to spend the winter months in the underworld, leaving a barren world during her annual absence. Eliot Coleman, a winter farming guru in northern Maine, was inspired by this story and coined the term Persephone Days to refer to the period in which day length drops below ten hours of sunlight. In Northern Indiana, this occurs from approximately November 10th through February 1st. This is significant because during this time, little to no plant growth occurs.
Due to this dormant period, we farmers must time our fall plantings perfectly. Our goal is to have everything between 75-90% mature by the time the Persephone period hits. If planting starts too late the plant will not reach maturity; too early and the crop will be overripe. Warm falls, such as that of 2016, complicate these calculations. The short days also force us to grow enough to pick over a three-month period, as crops require several weeks between pickings (as opposed to several days in the spring).
Less sunlight means less opportunity for the plants and the soil to dry out. On cloudy winter days, excessive soil moisture condensates on the plastic, giving the appearance that it is raining inside. Fungus and mildew thrive in dark, moist environments and can easily devastate an entire winter crop if it goes unchecked.
Since fungal diseases usually don’t show symptoms until it’s too late, prevention is essential. We promptly remove any dying plant residue immediately and terminate any sick plants. Tools and harvest equipment is cleaned regularly so as not to spread diseases. On sunny days, we “open up” the hoop by removing blankets to allow the plants to breathe and air to circulate around the base of the plants. We open vents for additional airflow and to allow the dry, outside air to suck out the moisture.
As you can now appreciate, winter farming has its challenges. But with proper planning and an eye on the weather, we can bring fresh veggies to your plate all season. When giving winter farm tours, I usually tell people to think of the hoop house as a large, living refrigerator. While the plants are alive, they are more or less dormant, waiting to be harvested and enjoyed even in the dead of winter.