Frost-free Dates Are Different Than Your Hardiness Zone

Frost-free Dates Are Different Than Your Hardiness Zone

Your Last Spring Frost and First Fall Frost Dates differ from your Hardiness Zones, they’re are two distinctly different things. Both are extremely valuable to know in achieving success in your garden.

Last Spring Frost and Fist Fall Frost Dates: What It Means To You

Native plants grow naturally and without problem where climate conditions are most suitable for them. When we plant introduced annual ornamental plants or garden vegetables and herbs they will usually adapt readily if climate and soil are suitable for them to thrive. This is important to know when growing annual plants, annual flowers, annual vegetables, and perennial seedlings.

Every year, we have two dates to be concerned with in all non-tropical climates: 1) the estimated last date of freezing in the spring, and… 2) the first date of estimated fall frost.

If there are any spring freezes, native plants are better programmed and adapted to wait for all frosts to pass before they begin growing.

Whereas, the annuals we love to put out into the garden every year for foliage and color lack the ability to survive any amount of frost or freezing temperatures.

Sometimes however, you may have experienced when you have planted annuals too early and for some reason they survived, while you may feel luck played a role it is more than likely that their survival was mostly due to the fact that you just happened to put them in and area that’s known as a ‘microclimate’.

Every garden has micro-climates, they are small areas that are protected by wind and frosts to some degree. For instance, the south side of your house will produce a micro-climate. Whereas a low laying area in your yard that dips down is quite likely to be the first spot that your annuals die, this is known as a “cold sink” (cold air sinks to the lowest laying land). Likewise, an area in your garden that is the last to get sun in the morning will also be a colder zone.

Observe your garden, where do you notice frost lingering in the early spring? Which area(s) of your garden do you see things blooming earlier?

While the right amount of heat and humidity are important for germinating seeds, excessive heat (above 90°F) can damage fragile annual and perennial seedlings.

If you want to know your average frost dates are this is a wonderful interactive map to find your first and last frost dates over at The Farmers’ Almanac – just click on your state and a little window will pop-up.

My Last Spring Frost date is March 28th, my First Fall Frost is November 5th.

Knowing these dates helps in being prepared for weather that could turn your gardening efforts into mush in one night.

Frost-free Dates Are Different Than Your Hardiness Zone

In the above image the dates listed are normal averages for a light freeze/frost in south eastern North Carolina, where I live. The possibility of a frost occurring after the spring dates and before the fall dates is 50 percent. Frost and freeze temperatures are categorized by their effect on plants:

  • Light freeze: 29 degrees F to 32 degrees F – tender plants killed, with little destructive effect on other vegetation.
  • Moderate freeze: 25 degrees F to 28 degrees F – widely destructive effect on most vegetation, with heavy damage to fruit blossoms and tender and semi-hardy plants.
  • Severe freeze: 24 degrees F and colder – damage to most plants.

You might also be interested in Help! What Should I do When There Is A Frost Or Freeze Warning?

Plant Hardiness Zones & Winter Temperature Extremes

Hardiness zones are determined by the United States Department of Agriculture (USDA). The USDA Hardiness Zone Map is the most common which determines a plants ability to live based on cold temperatures, not hot. This map is generally used for trees, shrubs and perennial plant hardiness.

  • When temperatures are too cold for an extended period, the plant’s ability to reproduce is curtailed where eventually the plant will die.
  • When temperatures are too high, plants dry out and die back.
  • Temperature influences plant growth. Every plant has high and low temperature extremes that they cannot endure.

Use this link to the USDA Plant Hardiness Zone Map – simply click on your state and a detailed map will display and you will be able to see which hardiness zone you’re located.

The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones. The map is now an interactive GIS-based map – meaning there’s a lot of detail and it is more representative of the zones, other maps I’ve seen are older and less accurate.

The USDA map tends to be more effective for the eastern two-thirds of the United States. This is because there are fewer mountains that influence cold air masses. In the mountains of the western regions of US there is much more profound impact within the climate, including more micro-climates. Micro-climates are weather conditions in a small area that can be different than other surrounding areas. The mountains along with the Pacific Ocean influence hardiness differently than along the east coast of the Atlantic.

The Hardiness Zone map is broken down into 11 zones, individual planting zones represents areas of winter temperature extremes throughout North America. The hardiness plant zone map does not take into consideration snow cover, precipitation, humidity, sunlight and seasonal winds.

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