How does frost affect carrot harvesting?

Frost affects carrots in a radical way. "A light frost below 40°F (4°C)" writes noted carrot grower John C. Hagan, "Will convert the starch into natural sugar and produce a sweetness in the carrot that is most excellent," but, "prolonged freezing more than 36 hours at a time below 15°F (-9°C)" sub-cellular processes begin to break down and the root is ruined. Knowing these temperatures allows us to reap the benefits and avoid loss: I plan my carrot harvests around forecasts of frost.

After several light frosts, sugar development has reached a peak within the plant. Enzymes are utilized to convert the complex carbohydrates stored in the roots into simple sugars. This process requires temperatures in the range of 32-40°F (0-4°C) for a minimum of 8+ continuous hours. An example of this would be carrots that I have harvested after the roots have undergone 5-6 frost cycles. The difference is very noticeable.

Every plant has its limits as to how much it can take before damage occurs. Below 25°F (-4°C), ice crystals begin to form. At 15°F (-9°C), complete freezing ruins everything, and the thawed roots are watery mush. There was a polar vortex, and I lost a crop once. Now I harvest at under 20°F (-7°C).

Harvest during the thaw in the middle of the day, when the soil is softening. Insert the thermometer 6 inches down. Only some will be above 25° (-4°C). Pull them out and heap up the others straight away before it refreezes. I use a grubbing fork, not a spade, as it causes less injury to the remaining roots.

Mulching protects the plants from severe cold. Apply at least 6 inches (15 cm) of straw before the first hard frost. Chopped straw keeps the soil from dropping below critical temperatures. In my Zone 5 garden, the mulch keeps the roots harvestable all winter long. Check all beds after snowstorms or high winds have passed.

Read the full article: 5 Key Signs: When to Harvest Carrots Perfectly