The Growing Season
Frost-free days are your gardening window of opportunity. During the growing season, plants have time to mature, blooms to form and fruit or vegetables to ripen. Most vegetables purchased, whether seed or seedlings, will have a "days to maturity" listed on the tag or package.
Frost dates are based on historical data compiled by the United States Department of Agriculture, and should be used as a reference. The chance of an early or late surprise frost is always a possibility. The probability of frost or freeze is greatly affected by elevation, the direction of sunlight (north, south, east or west), prevailing winds and other factors. Cold air "drains" or flows down slopes to create frost pockets at the base of the slope. Valleys are more susceptible to frost. Areas near lakes or ponds are less likely. Spots sheltered by buildings get additional protection. A light breeze can reduce risk of frost, a cold wind can turn a mild frost into a killing freeze.
Frost or Freeze
Frost occurs when the temperature reaches 32 degrees Fahrenheit or below and water vapor freezes on a surface. It usually occurs on a clear night when heat radiates up from the ground. Tiny ice crystals form when water vapor condenses. Similar to dew, the temperature at ground level is the key. The temperature there is often colder than the air temperature just a few feet higher. Tender plants need to be covered for protection from frost.
Freeze involves a 32 degree Fahrenheit surface temperature that lasts for a significant length of time. Frost is not necessarily present. Vegetation damage is usually a result. Hard freeze is usually defined as 25 degrees Fahrenheit or below. The term killing freeze or frost depends upon the hardiness of the plant and the level of exposure.
Freeze warnings are issued in fall as the first frost and freeze conditions begin to appear and can occur in early spring as well. Use the information below to find the estimated dates for first frost and last frost in your USDA zone.
First and Last Frost Dates
USDA Zone 1
- Last Frost Date: June 15
- First Frost Date: July 1
- Minimum Number of Frost-Free Days: 30
USDA Zone 2
- Last Frost Date: May 15
- First Frost Date: August 15
- Minimum Number of Frost-Free Days: 90
USDA Zone 3
- Last Frost Date: May 15
- First Frost Date: September 15
- Minimum Number of Frost-Free Days: 120
USDA Zone 4
- Last Frost Date: May 15
- First Frost Date: September 15
- Minimum Number of Frost-Free Days: 120
USDA Zone 5
- Last Frost Date: April 15
- First Frost Date: October 15
- Minimum Number of Frost-Free Days: 180
USDA Zone 6
- Last Frost Date: April 15
- First Frost Date: October 15
- Minimum Number of Frost-Free Days: 180
USDA Zone 7
- Last Frost Date: April 15
- First Frost Date: October 15
- Minimum Number of Frost-Free Days: 180
USDA Zone 8
- Last Frost Date: March 15
- First Frost Date: November 15
- Minimum Number of Frost-Free Days: 240
USDA Zone 9
- Last Frost Date: February 15
- First Frost Date: December 15
- Minimum Number of Frost-Free Days: 300
USDA Zone 10
- Last Frost Date: January 31
- First Frost Date: December 15
- Minimum Number of Frost-Free Days: 315
USDA Zone 11
- Last Frost Date: No Frost
- First Frost Date: No Frost
- Minimum Number of Frost-Free Days: 365
Protecting Your Plants from Frost
Tender, herbaceous plants are more likely to suffer from frost than hardy woody plants. When sustained temperatures are at freezing or below, long-term protection is usually not feasible. But in the event of an early fall or late spring cold snap, you can provide temporary protection.
Methods of safeguarding plants vary. You can cover plants with specially designed row covers or common household items such as cloth, paper or plastic. In extreme cold, try to prevent the cover (especially plastic) from contacting foliage. The contact will conduct the cold and can damage the leaves.
A simple wooden frame can be draped with the cloth or plastic sheets. The radiated heat will be kept inside.
A layer of mulch will also help retain the heat from the soil to protect from cold.
You can keep a garden journal and record your own garden weather data. For advanced warning of cold weather listen to the weather on television or radio.
Frequently Asked Questions About Frost Dates
When you know the frost dates for your area, you can maximize your gardening efforts. Take a look at answers to these common questions about frost dates and see how you can get an early start with planting.
What Can You Plant Two Weeks Before the Last Frost?
Carrots, broccoli, beets, lettuce and turnips are examples of vegetables you can plant from seed a couple of weeks before the last frost. If you're planting a flower garden, you can seed flowers such as sweet alyssum, forget-me-not, larkspur, coreopsis, pansies, snapdragon and marigold two weeks before the last frost.
What Can I Plant Five Weeks Before the Last Frost?
There are some things you can plant as early as five weeks before the last frost. If you want to get an early start on a vegetable garden, you can seed beets, carrots and peas. Pansies and violas are two annual flowers you can plant five weeks prior to the first frost. Once the soil is no longer frozen, you can plant many dormant, bare-root perennials. Always check the plant tag or seed packet for planting guidelines for your specific plants.
Why Are Frost Dates Important?
Knowing the first frost date in the fall and last frost date in the spring will help you plan your garden. The dates are also crucial to the health of the plants since frost can damage or even kill some plants. In some cases, planting too early (before the last frost date) can send a plant into dormancy. If you know your last expected frost date, you've got a good idea of when you can start planting. Your first frost date will give you an indication of when you need to collect your final harvest.