How to use your hardiness zone.
Some plants will adapt to a variety of conditions, including soil type, watering fluctuations, and humidity differences, but most plants will only tolerate a specific degree of chill in the winter. That’s where hardiness zones come in—they list the average lowest temp in every area of the country, so gardeners can select perennial plants that will survive the type of winters common to specific regions.
Use a hardiness map to find the average lowest winter temperature in your community and then choose plants that will survive that temp. To simplify the process, most commercial greenhouses provide detailed plant labels that list suitable hardiness zones, the lowest temperatures the plants can survive, and other vital information, such as whether they will grow better in the sun or shade.
Use a zone map as one factor in choosing a plant. However, don’t forget to check off all the boxes on its other needs.
- Maximum temperature
- Precipitation
- Average frost dates
What are Frost Dates?
A frost date is the average date of the last light freeze in spring or the first light freeze in fall.
The classification of freeze temperatures is based on their effect on plants:
- Light freeze: 29° to 32°F (-1.7° to 0°C)—tender plants are killed.
- Moderate freeze: 25° to 28°F (-3.9° to -2.2°C)—widely destructive to most vegetation.
- Severe freeze: 24°F (-4.4°C) and colder—heavy damage to most garden plants.
Note that frost dates are only an estimate based on historical climate data and are not set in stone. The probability of a frost occurring after the spring frost date or before the fall frost date is 30%, which means that there is still a chance of frost occurring before or after the given dates!
Frost is predicted when air temperatures reach 32°F (0°C), but because it is colder closer to the ground, a frost may occur even when air temperatures are just above freezing. Always keep an eye on your local weather forecast and plan to protect tender plants accordingly. Weather, topography, and microclimates may also cause considerable variations in the occurrence of frost in your garden.
Last and first frost dates are 30% probability. Calculated using 1991-2020 Climate Normals from NOAA (National Oceanic and Atmospheric Administration).
On the reverse side of most seed packets will be a map of the suggested outdoor sowing months for areas, sowing instructions and information on the variety such as how deep to plant, how many days to harvest, light requirements (full sun, part shade, etc.) and plant size and how long till the seeds emerge (7-10 days from sowing).
With your own knowledge and the information above you can decide what plants/seeds to start indoors and when to start plants/seeds outdoors.
Happy Gardening!
