Why Does the Kale Taste Better Harvested after First Frost?

Kale is a cold-hardy vegetable.  For a long time I've wondered why it tastes better in the Fall than in Summer.  I finally found an answer in Jeff Ashton's book The 12-Month Gardener: Simple Strategies for Extending Your Growing Season.  He says, "...collards, mustard greens, Brussels sprouts, cabbage and kale will mature very well in the summer, but that doesn't mean they should be harvested in hot weather."

Why?  They are bitter (to varying degrees) he notes, when harvested then.

Why?  "Sugar (generated by photosynthesis) is the fuel that allows a plant to breathe.  In times of high stress, hardy plants are using every bit of sugar available to stay alive.  Bitterness is a result of sugar depletion during these periods of high stress when temperatures soar and the soil is dry."   Ashton observes, as do I, that they become much sweeter after being hit by a couple of frosts.

Why?  "The reason for this" he says, "is that the rate of respiration in hardy vegetables slows down in cool weather.  As the season progresses into cooler weather, excess or unused sugar is stored."  Mmmm.  Hence, sweeter leaves!

HARVESTING
In summer, if you must harvest your kale, make sure it is well-watered ahead and harvest after a couple of cloudy days for a sweeter experience.  Otherwise, wait until Fall's frosts have hit to experience the optimum flavor.

In our Garden, kale has been observed to winter over, especially if covered even lightly with the spun material (often called Reemay) that lets in sunlight and rain. Harvest can even take place during winter on more mild days.  I harvested both curly and lacinato (dinosaur) kale this week.

Beware! During the Fall and Winter, whiteflies can be a pest you don't want to bring indoors, especially if you have houseplants.  Shake harvested leaves while still in the Garden and wash well or submerge in water to remove any remaining flies before bringing indoors.