by Sarah West
Winter farmers’ markets offer two basic categories of produce: storage crops and cold hardy crops. We know the characters well—whiskered roots, boxes of potatoes blinking in the daylight, stoic winter squash, bunches of bitter greens, snow-white leeks, fluffy blends of salad leaves looking like a pile of delicate miracles. We are lucky in our climate to enjoy a wide range of fresh vegetables throughout the cold season, from bunching greens to rutabaga, tonic to starchy sweet.
Storage crops are typically harvested in fall or early winter and held in barns or cellars at a temperature that protects them from freezing or sprouting. Cold hardy crops are planted in early fall and kept in the ground through winter, growing slowly and providing ultra fresh food at a time of year when it is much harder to find.
This year, hardy crops in our area faced an exceptional winter foe. Temperatures two weeks ago reached near record lows, dipping ten degrees below zero in Eugene area and hovering between six and ten degrees above zero around Portland. They were the kind of temperatures we rarely see west of the Cascades, for which farmers would be foolish to prepare defenses. The added cost of the necessary protections required to successfully grow cold hardy vegetables in sub-freezing temps is significant and largely unnecessary in our region most years.
As sure as any average is the occasional anomaly. We are tempered to expect mild winters and even in the wake of ominous forecasts, it can be hard to know how bad a freeze will be. Though area farms endured over a week of freezing temperatures, moderate cold can sometimes do more good than harm to edibles. A few seemingly insignificant degrees can mean the difference between frost-sweetened or frost-killed vegetables. And it is difficult to tell which fate has befallen your fields until they’ve thawed.
Many winter vegetable varieties are built to withstand a certain amount of cold, especially if it arrives incrementally. In a process known as “hardening off,” plants initiate subtle shifts in their physiology, making their cell walls more permeable to water (to allow movement of expanding fluids and avoid cell rupture) and increasing the sugar content of their cells’ cytoplasm. Sugar solution has a lower freezing point than water, thus acting as cellular antifreeze in a properly hardened plant.
Despite these clever defenses, physics demands that water turn into ice under 32-degrees Fahrenheit. When a vegetable plant is exposed to sub-freezing air, the water between cells inevitably forms into ice crystals, a process that attracts additional water from inside the cells. As the ice crystals grow, the plant responds again by increasing the sugar content of the cytoplasm, improving its ability to prevent ice formation inside the cells.
Winter vegetables can endure this game for a bit (typically to around 15-degrees), but if the temperature remains advantageous for ice, the cells will eventually become dehydrated and die. Add to this process the additional cooling and drying effects of wind chill on exposed plant tissue, and the chances of a field planting of broccoli or kale surviving our recent cold snap look ominous at best.
Crops under various forms of protection (plastic high-tunnels or row cover cloths) may have gotten the 3- to 6-degree buffer necessary to pull through. In most cases, it comes down to location. If the field is in a protected site (away from wind or cold pockets), got enough snow cover to act as insulation or stayed in the warmer range of our recent lows, its crops might have pulled through.
Farmers are a resilient lot. Though this winter’s cornucopia may look slightly less magnificent than years’ past, know your able farmers are already plotting the next round, adding this anomaly to their seasoned calculations, taking the good with the bad because they know, as some of us forget from time to time, that the two are always inseparable.
“Don’t worry and fret about the crops. After you have done all you can for them, let them stand in the weather on their own.
If the crop of any one year was all, a man would have to cut his throat every time it hailed.
[…] the real products of any year’s work are the farmer’s mind and the cropland itself.”
(from Prayers and Sayings of the Mad Farmer)