Frost dates determine when to plant

Published 7:44 am Wednesday, October 7, 2009

Years ago, the term “frost zone”, meant absolutely nothing to me. Now I realize that the “frost zone” is an important presence in the world of gardening, revealing information that is useful to all gardeners.

As you start planning your garden, planting zones and frost dates must be considered.

Accurate selections of garden and landscape plants depend on this information for their survival.

Plant hardiness zones divide the U.S. into 11 planting zones based on a 10 degree Fahrenheit difference in the average annual minimum temperatures.

An example is that the average annual minimum temperature in zone 2 is -50 to -40 degrees Fahrenheit, and the average annual minimum lowest temperature in zone 10 is +30 to +40 degrees Fahrenheit.

There are also different climates and frost dates within planting zones in a region due to the topography, lakes and rivers, canyons or mountains.

These can cause altered air flows, which can raise or lower the temperature as well as zones.

We in this area that have been considered to be zone 7, have slid into zone 8 as well, due to the fluctuating air flow.

Other factors that will effect plant hardiness are the chemical balance and texture of the soil, exposure, altitude, rainfall, humidity, sun light levels, wind and wind chill factors.

When selecting plants and shrubs, the hardiness rating is considered, since some will not survive severe winters, others will wither in heat and many spring-flowering bulbs and trees need a cold period to stimulate their growth cycles.

Plants usually survive the cold better in a dry area.

Deciduous plants tolerate more exposure and the summer heat. Evergreens prefer a sheltered area with more humidity and cooler summers.

Zone 7 — Average dates of last frost are March 30 to April 30. Average date for the first frost, which we haven’t had to worry about lately, was Sept. 30 until Oct. 30. Average dates of the last frost are usually Feb. 28 til March 30 for zone 8 with the first frost date being the same as zone 7.

Frost occurs around 32+ degrees — light freeze with damage depends upon the duration of the frost, humidity, topography, etc.

A light freeze, 29F to 32F, will kill all the tender plants.

A moderate freeze, 25F to 28F, will damage most vegetation with heaver damage to fruit blossoms. Severe freeze, 24F and colder, means damage to all but the hardiest of plants.

Mother Nature will have her way and gardeners continue to do what they can to stay balanced. A joint effort is needed to succeed in gardening between the forces of nature and our desire for a successful outcome.

Gwen holt is a master gardener from Isle of Wight. Her e-mail address is Virginia Master Gardeners are volunteer educators who work within their communities to encourage and promote environmentally sound horticulture practices through sustainable landscape management education and training. As an educational program of Virginia Cooperative Extension, Virginia Master Gardeners bring the resources of Virginia’s land-grant universities, Virginia Tech and Virginia State University, to the people of the commonwealth.