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Zones - How important are they?

The answer to this question is "Very". Plain and simple.

Let's begin by understanding what the growing season is for a particular area. It is those number of days between the last frost in the spring and the first frost in the fall. This may be not all that important or critical for fruits, perennial flowers, trees and shrubs (this is where stretching the zone comes into play, later), but for vegetables and annuals, it is.

The Growing season for your zone

The growing season is the total number of frost free days.

The United States Department of Agriculture did a study of average annual minimum temperatures throughout North America.

This USDA Plant Hardiness Zone Map reflects the ability of a plants hardiness. What temperature will a particular plant withstand in regard to its minimum tolerant degree.

The following is a chart of the USDA zones and their frost dates.

Zone Last Frost
First Frost
Number of frost
free days
1 June 15 July 15 30
2 May 15 August 15 90
3 May 15 September 15 120
4 May 10 September 15 125
5 April 30 October 15 165
6 April 15 October 15 180
7 April 15 October 15 180
8 March 10 November 15 245
9 February 15 December 15 265
10 January 20 December 20 335
11 Frost Free 365

Zone 1 has the distinction of being susceptible to frost virtually all year long.

Keep in mind this is just one of the factors, aside from, moisture, soil, fertility, humidity, drainage that will gauge a plants success.

Choosing Varieties

It is particularly important to know your zone and to get a general idea of the dates. No two years are going to be the same. Sometimes spring arrives early and sometimes very late. The same goes for the end of the growing season in the fall.

Going on that basis, choose varieties that are specific to your zone.

Remember, some varieties may grow in your zone and some will not. There are exceptions to this rule and that is known as stretching the zone with micro climates and gardening aids.

Most seed packets will give information such as "120 days growing time" (i.e.. Zone 1 is in trouble).

But more importantly, nurseries do not necessarily sell things that grow just for their area. We would like to think they do, but every so often other plant material appears. Just double check and be safe.

Stretching the zone

Now what about stretching the zone requirements to get more growing days? Especially for vegetable and sneaking in some annuals and perennials, you might want to try creating a microclimate. Brick walls, stone fences, raised beds, sheltered garden areas may all help.

Basically, you are trying to fool Mother Nature and this may or may not work.

Another way to stretch the growing season or zone for annual seeds is to start indoors. Plant early and you will have a jump on the frost date. Your plant will be weeks ahead of schedule.

The use of cold frames is another way to speed up germination and also will provide frost-free shelter. The options of propping the top to allow for ventilation and then lowering for the evening to conserve the heat of the day is great.

Another stretcher is hot caps. These individual protectors will protect from possible early or late frost. Commercially, some are fiberglass, but you can make some from large plastic milk jugs.

Choches are known from the Victorian days. Glass bells to protect the plants. Now, from the same concept there are water-filled cloches. Using the heat's sun rays from the day, where heat is released for evening protection.

Row covers will help extend your growing days. Often, lightweight synthetic fabrics can be used. These are known as floating rows.

A somewhat costly method, if you are paying for water, is to turn on a very fine spray from your garden sprinkler. If the temperature drops below 33F keeps the misty spray on until the sun pops up. this is often done by commercial growers where frost is not generally expected.

And, lastly, fooling Mother nature entirely is to grow in a greenhouse. It's Zone 4 on the outside, but a nice tropical Zone 10 all year round inside. What could be more wonderful? The ultimate dream of many gardeners.

Another Consideration - Heat

With global warming, zones may be tested in several other ways. That's why the next consideration should be the Plant Heat Zone Map put out by the American Horticultural Society.

USDA hardiness zone map on the Internet (with close-up of your area): http://www.usna.usda.gov/Hardzone/

European Zone Maps

Many Emily readers have asked about USDA equivalent European Zones. You might want to take a look at one of these European Zone maps to see if they are helpful.

The Swedish Fuchsia Society's map: http://www2.dicom.se/fuchsias/eurozoner.html