What is my USDA Hardiness Zone?

How to get in the zone with your USDA hardiness zone.

When it comes to xeriscaping, the most vital piece of information resides in your local climate and understanding what plants can survive and thrive in your hardiness zone. Hardiness is the basic measure of what plants can withstand the coldest temperatures experienced in your location. In this article, you’ll learn the answer to “What is my USDA hardiness zone?” and how to begin planning your xeriscaping project based on understanding your hardiness zone.

Origins of Hardiness Zones

The concept of hardiness zones has a rich history spanning almost a century. In 1927, researchers at the Arnold Arboretum of Harvard University developed the first climate-based zone map in the United States. This original black-and-white map, updated several times over the years, consisted of eight zones that helped people assess the winter survivability of various trees and shrubs in specific regions.

The 1948 version of the Arnold Arboretum map introduced 10 color-coded zones, each representing the lowest average temperature experienced during the coldest month. These zones varied in their degree separation, ranging from 5 to 15 degrees.

In 1960, the United States Department of Agriculture (USDA) launched its own Plant Hardiness Zone Map, utilizing weather data similar to the Arnold map. However, the USDA made a significant change by dividing the country into 10-degree zones, creating uniformity. In 1990, the map was further refined, incorporating an “A” and “B” system that subdivided each zone into two 5-degree sub-zones.

The most recent update to the USDA’s Plant Hardiness Zone Map was released in 2012, resulting in a version featuring 13 zones, each with an “A” and “B” subzone. You can determine your zone by finding your area on the map, matching the color code, or using the USDA’s website tool that allows you to discover your planting zone via zip code.

The Role of Hardiness Zones in Xeriscaping

To grasp the impact of hardiness zones, let’s consider some examples. Columbus, Ohio falls into Zone 6a, while Houston, Texas resides in Zone 9a. Southern Minnesota lies in Zone 4b. But how does this information influence your plant choices?

Many perennials, shrubs, and trees come with labels indicating their compatibility with specific hardiness zones, alongside details about light requirements and projected sizes. These zone assignments are based on plants’ known ability to tolerate low temperatures.

It’s important to note that hardiness zones primarily relate to a plant’s cold tolerance and are less relevant for annuals, which complete their life cycle within a year, or tropical plants like houseplants that don’t undergo full dormancy during winter.

Additional Factors to Consider

While hardiness zones provide a starting point, successfully cultivating cold-hardy perennials and other plants involves considering various factors beyond these zones. Dave Whitinger, executive director of the National Gardening Association, emphasizes the importance of examining other environmental aspects such as soil acidity or alkalinity, precipitation levels, elevation, thawing and frost dates, and snow accumulation. These factors are equally critical alongside winter temperatures.

For example, Los Angeles and Miami both fall into the same hardiness zone, 10b. However, their climates differ significantly. Los Angeles experiences a dry, mountainous environment with notable temperature fluctuations throughout the day, while Miami has a wet, low-lying landscape with relatively stable daily temperatures. Although orange trees thrive in both regions with proper watering, cacti flourish in Southern California’s arid climate but struggle with South Florida’s subtropical rain.

Snowfall also plays a vital role. Snow-covered regions like New York, despite being classified in colder hardiness zones, can grow plant varieties that may struggle in warmer zones. New Yorkers have successfully cultivated fig trees by protecting them with snow, which acts as an insulator, keeping the ground temperature beneath it warmer than the air. Conversely, regions further south with milder winters lack this insulating snow, potentially subjecting plants to lower temperatures.

Choosing the Right Plants

While no universal map provides precise guidelines for your unique backyard conditions, numerous resources can assist you. Whitinger suggests consulting your local extension service, which collaborates with land grant universities nationwide to conduct research on various topics, including plants. These services offer scientifically accurate guides, articles, and location-specific information. Many extension services have informative websites, and you can reach out to them directly for personalized advice. They can recommend native plant varieties and suitable fruits and vegetables for your area.

Your local independent garden center or nursery is another valuable resource. These businesses specialize in growing plants adapted to your region and possess extensive knowledge about the best tomato varieties for your summers and common pests you may encounter. They can also guide you on the optimal timing for planting your flowers in spring, reducing the risk of late frosts.

Remember, as you gain gardening experience, you’ll develop valuable insights specific to your own yard. Begin by identifying your hardiness zone, and then expand your knowledge. By embracing xeriscaping principles and considering various environmental factors, you can create a stunning, water-efficient garden that thrives within your specific climate zone.