Picture of Dawn Redwood tree in the distance in front of a fence
Beginner Gardening

How to Determine Your Area’s Frost Dates

Learn about your zone’s frost dates and planning your growing season

Beginner’s Guide to Gardening

Picture of Dawn Redwood tree in the distance in front of a fence
Dawn Redwood at Cedar Homestead in Winter

Introduction

I’m determined to create a series of posts for the beginner gardener. Whether you’re brand new and just starting out, have been gardening for a little while already, or even if you’ve been gardening for quite some time but want to see what others are up to, this is for you. 

The thought of planting your garden can be very exciting! But before running outside and planting, it helps to do a bit of planning. In my blog post, ‘How to Plan Your Vegetable Garden: The Five Most Important Things to Know’, I provided a glimpse at what it looks like to start planning a garden. 

The post discussed a few topics:

  • Plant hardiness zones – how to determine which gardening zone you’re in. 
  • Growing seasons – familiarizing yourself with the seasons in your area
  • Plant families – learning about the plant families to have a better understanding of how they grow, what temperatures they can tolerate, learn about common pests and companion planting
  • Plotting out what to plant and when – when is the appropriate time to plant your garden, whether the plants are appropriate for your area, planting what you eat.
  • Soil composition and what makes your plants thrive – learning about the building blocks in your soil for healthy plants

We’re going to be honing in a bit more on the plant hardiness zone and focus on determining frost dates.

What are frost dates?

Before diving into frost dates, get to know your climate. Does your climate get frost? If not, then you will not have to worry about pinpointing frost dates. However, I think it’s a good idea for those who don’t commonly get frost to still be on the lookout in the forecast. It would therefore be helpful for someone to understand what temperatures their plants can tolerate. In areas that do have frost, there are two frost dates that will have to be marked on your calendar – a first frost date and a last frost date.

What is a ‘first frost date’?

The first frost date is the first date in the fall or winter that your area will have frost.

What is a ‘last frost date’?

The last frost date is the last date your area is forecasted to have frost in the spring.

The NOAA and Calculating Frost Dates

The National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Environmental Information collects a variety of data, which helps to calculate frost dates. 

They are the “Nation’s leading authority for environmental data, and manage one of the largest archives of atmospheric, coastal, geophysical, and oceanic research in the world. NCEI contributes to the NESDIS mission by developing new products and services that span the science disciplines and enable better data discovery.”

Classification of Freezing Temperatures

There are 3 different classifications of freeze temperatures that you should be aware of: light freeze, moderate freeze, severe freeze.

Determining Frost Date: Regional, Zip Code, and Microclimates

Determining frost dates in your area is really important. It can literally mean the difference of life and death of your plant. For instance, transplanting a tomato plant outside when frost is in the forecast is not the best idea. Tomato plants are frost tender and cannot tolerate frost. They are really not good at handling anything below 50-60 degrees Fahrenheit. 

It’s important to keep in mind that the regional frost dates, like those provided by the USDA Plant Hardiness Zones, are only a guide and not exact or foolproof. The noted frost dates are based on historical climate data and do not take into account factors that may affect future climate or weather changes. 

Determining Frost Dates by Zip Code

Determining frost dates by zip code is also a general guide, and will not be entirely accurate.

Microclimates on Your Property

Each property has its own microclimates that differ from gardening zones. Start making note of how the sun touches (or exposure) each part of your property. There are 4 different microclimates to be aware of on your property:

  1. Southern exposure – most heat and light

    a. For example, our side yard faces south. It receives the most amount of heat and sunshine and there are no trees. However, it’s important to note that there is some shading depending on the proximity of plants next to our garage.
Southern facing side garden with seedlings in late evening
  1. Northern exposure – weak, little to no exposure to the sun

    a. On our property, we have a section that gets very minimal sun. It will only get sun in the late evening since it’s located in the northern part of our property, but also blocked by our house. We have plants that thrive in little exposure to full shade, like ferns. This area of the property also has snow that keeps for quite some time in comparison to the rest of the yard.
  2. Eastern exposure – sun in the morning (coolest part of the day)  and may have shade later in the day, thereby avoiding the hottest temperatures.
  3. Western exposure – shaded in the morning and exposed to sun later in the day (afternoon, late afternoon, and evening). Plants will be exposed to the hottest temperatures during the day.

Besides sun exposure, there are other microzones to make note of:

  • Natural slopes
  • Wind breaks
  • Rock, cement, walls, and even fences

Local Forecast

When evaluating when to begin transferring plants or direct sowing outside, I look at least two weeks ahead at the local forecast. For my area, the last frost date for spring is between May 5 to May 20. However, we’ve experienced an unexpected snow in early May two years ago, and freezing temperatures up until May 20 in 2021. For now, I’ve marked my last potential frost date as May 20. However, it is possible this year that the last frost date can be sooner during the month of May.

Refer to Your Local Extension Office

For further help, refer to your Local Extension Office, or also known as Cooperative Extension. The Spruce discusses what an extension office is and how it can help you in their article, “What Is an Extension Office? Here’s What Can It Do for You. A Place to Get Research-Based Information for Your Location”.

To locate an Extension Office near you, conduct a search by ‘extension office’ results will populate. Since I’m in New Jersey, we have Cooperative Extension offices divided up by county that are listed on the Rutgers University New Jersey Agricultural Experiment Station website.

What zone are you in and does your area deal with frost? Share below what you experience as you prepare for the growing season!

Resources

Farmer’s Almanac

National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Environmental Information 

Rutgers University Cooperative Extension County Offices

USDA Plant Hardiness Zone Map

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