Jessica Damiano's award-winning garden blog gets to the root of things.
Frost vs. Freeze: What's the difference to plants?
It's snowing outside, and my thermostat tells me it's 34 degrees, but this could only be the tip of the iceberg, so to speak: Long Island could be headed into a deep freeze this week, beginning with potentially plant-killing temperatures tonight into tomorrow morning. If you haven't already, bring in your tropicals, tender perennials, herbs and vacationing houseplants -- immediately.
What we're expecting is a freeze, not a frost. To gardeners, both terms are cautionary, although many -- even long-term, successful green thumbs -- can confuse the two. Here's the difference:
Frost: Think of frost as frozen dew. The ground or other surface temperature drops below freezing when the ambient air temperature is warmer, causing the water vapor to turn into ice crystals on the soil (or car windshield) surface. Frost typically occurs overnight in windless conditions under a clear sky. Actively blooming plants, most summer annuals and tender perennials are susceptible to frost damage and should be covered with fabric overnight when frost is expected. Larger plants can be wrapped in bedsheets and loosely tied with twine. (October 15 is the average first frost date on Long Island, but it can be sooner or later.)
Freeze: Cold air, often exacerbated by cloud cover and wind. The temperature drops below 32 degrees for at least a few hours. Plants can be damaged. (November 1 is the average first freeze date on Long Island.)
Deep freeze: Same as a freeze, except the temperature remains below 28 degrees.
If you have trees that require winter protection, such as fig trees, cover them with a breathable fabric on a dry, cloudy day, delaying the process for a few days after rainfall, if necessary, to ensure plant parts are completely dry before wrapping. Never use plastic because it can trap moisture and encourage condensation, which could harm the plant.