November 21, 2021
Cold Prep (or not)
by Farmer Derek

All season long we monitor the overall weather forecast but this time of year we focus more on the temperature than the precipitation prediction. Because just about everything we're currently harvesting is under protection in a tunnel and we're no longer disturbing outside soil, rainfall doesn't matter so much. We're still retrieving field kale because that has a very high tolerance to cold and sometimes even overwinters. All other crops, plus additional kale, reside inside. However, those cold tolerant crops have a varying degree of ability to withstand cold temperatures. Aforementioned kale, as well as spinach, are the most hardy, followed by bok choy, arugula, mustard, chard, and lettuce. Age of the crop matters too. Generally, younger is hardier if mature crops spent most of their life growing in warmer conditions.

At this point all of the crops in the tunnels have been exposed to sub-freezing conditions a few times so they should be fairly well acclimated. The roof overhead prevents moisture from settling and freezing on leaf surfaces and causing frost damage that way. During the day the sun heats the indoor space and closing it up at night hopefully traps some heat to keep tunnel temperatures warmer than outside. If nighttime temperatures are forecast to bottom out in the low 20s or teens we erect an interior tunnel which adds even greater protection by keeping warmer air right around the plants.

Over the years crops have survived and gone on to thrive even after single-digit outdoor temperatures. Interior covers kept the temperature in the mid and upper 20s around the plants. They froze, looked lifeless on the ground, then a few days later after temperatures warmed a bit, they perked up and resembled their good old selves.

This coming week I'm now seeing lows forecast in the mid-20s which is on the cusp of breaking my low-temperature-confident-no-damage-will-occure threshold. I may hold out and give full trust to the plants, or I may give in and provide the extra protection. Why not just add the extra cover and be done with it? Good question. Trying to erect interior hoops around large and mature plants is challenging to accomplish without damaging the crops or getting them dirty. Putting extra covers over the hoops traps more moisture and can sometimes promote mold/rot/decay due to lack of airflow and requires removal during warm sunny days. The covers can be a pain to work with due to their size. Why do it if the plants don't really need it? Hopefully growing during this time of year for 10 seasons now enables us to better predict an outcome and avoid either unnecessary work or unnecessary damage. We shall see.