Growing Concerns: Don’t let a little frost put your garden on ice

September 30, 2018

Frost is a dirty word in the garden world. It signals that the end of the garden season is near. A freeze can put a quick end to the garden season.

What is the difference between a frost and a freeze?

A freeze is when the temperature dips below freezing. A frost can occur when the temperature is above freezing. A frost relates to the amount of water in the air.

There are two ways to measure the amount of water in the air. One is relative humidity, which measures the amount of water in the air compared to the maximum amount of water vapor the air can hold. At saturation, the relative humidity is 100 percent.

The other measure is dew point, which measures absolute amount of water in the air. The dew point is the temperature at which the air is saturated and relative humidity is 100 percent. For a given volume of air with a set amount of water vapor, the relative humidity varies with the temperature, but the dew point is always the same. If the dew point is above freezing, a frost is unlikely but if the dew point is below freezing, then a frost is likely.

Freezing temperatures do have some benefits. One is killing those pesky insects. Another is creating tastier vegetables. There are several vegetables that taste sweeter after a freeze.

Plants are composed of 90 percent water, and the water inside a plant can freeze during a frost. I use the word “can” because some cool-season plants are frost-tolerant. These plants prevent internal water from freezing by producing more sugar, which lowers the temperature at which the tissue will freeze. This is known as freezing point depression.

The dissolved sugar molecules interfere with the formation of ice crystals. The sugar gives the plant a sweeter flavor.

The root crops — beets, carrots, turnips and parsnips — are tastier after a freeze, but remember to harvest before the ground freezes. Leeks are more flavorful after a freeze and should also be harvested before the ground freezes.

Members of the Brassicaceae family, including broccoli, cauliflower, kale, cabbage and Brussels sprouts, all taste better after a freeze. The plants in this family grow better in cool environments. The plant works hard to prevent cells from freezing by sending sugars to the cells in the leaves or preventing the sugars that were produced during the day in the leaves from moving to the roots.

These hardy vegetables can survive temperatures as low as 20 degrees. After thawing out, these vegetables will continue to grow between freezes. Even after the tops of root crops like carrots are killed off, the roots will remain in good condition until the ground freezes. Keep the ground from freezing with a generous layer of mulch and you can harvest root crops all winter.

Fall has arrived. It is time to accept that the growing season is coming to an end. However, there is still plenty of time for a bountiful harvest of cool-season vegetables. Enjoy the sweet bounty!

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