Hardiness Zones, Heat Zones and Ecoregions

Hardiness Zones

A hardiness zone indicates the minimum winter temperature in your area, helping you choose which trees, shrubs, and perennials are hardy enough to withstand your area’s coldest winter temperatures and return year after year.
Tarrant County is primarily Zone 8b, with average annual minimum temperatures of 15 degrees F to 20 degrees F based upon the 2023 USDA update. Some portions of northern Tarrant Countymay be in Zone 8a.
Hardiness zones are based on only one factor: 30 year averages of temperature.
Therefore, other factors like extreme weather and microclimates in the area such as valleys that can have colder air, or rocky areas that reflect more heat, are not a factor in this calculation.

Ecoregions inform decisions about which native plants are best suited to the local climate and soil, promoting healthier, more resilient landscapes.
Ecoregions are formulated by assessing:
- Climate, Geology and Soil
- Landforms and topography
- Availability and movement of water, including rainfall, rivers and aquifers
- Vegetation and Wildlife
- Land Use such as urbanization, farming, ranching and timber production
Tarrant County is comprised of Western Cross Timbers and Grand Prairie
Each ecoregion has unique soil, climate, and rainfall patterns. Selecting plants native to your ecoregion ensures they are well-suited to the local conditions, requiring less maintenance and resources while thriving naturally.
Native plants are essential food sources and habitats for local wildlife, including pollinators like bees and butterflies.
Using native plants suited to your ecoregion reduces the need for excessive watering, fertilizing, and pest control.

For more information see Texas Ecoregions.

The heat zone map indicates the average number of days when temperatures exceed 86°F (30°C) in a region.
Tarrant County is in Heat Zone 9, which means there are on average 120-150 high heat days.
Heat zone data is not always included in plant catalogs or labels. When present, it is often displayed alongside hardiness zone information, creating a two-part code for plant cultivation.

For more information see Texas Heat Zones (US).

High temperatures, particularly above 86°F (30°C), can significantly affect plant biology, influenced by factors such as water availability, duration of heat, and plant type.
Heat causes increased transpiration, leading to quicker water loss, dehydration, and wilting. This water loss reduces photosynthetic productivity, limiting growth.
Most plants can cope with heat until around 86°F, but prolonged exposure can hinder recovery more than the temperature itself.
Plants employ various coping mechanisms, such as closing stomata to reduce water loss, which also limits carbon dioxide intake for photosynthesis.
While short periods of high heat may have minimal long-term effects, extended heat can stunt growth, inhibit flowering, and lead to fruit loss and leaf drop.

Water: Water is crucial for helping plants manage high temperatures. To minimize heat damage, ensure plants are adequately watered during heat waves.
Watering Timing: Water early in the day to allow plants to absorb moisture before peak evaporation.
Watering Method: Focus on the base of the plant to avoid leaf scorching from water droplets.
Mulching: Use mulch to retain moisture and regulate soil temperature
Shade: Consider temporary shade cloths to balance water loss and photosynthesis.