Why Should I Learn Plant Hardiness Zones and Heat Zones?

Updated: October 26, 2022

USDA  plant hardiness zone and AHS heat zone maps tell you the same thing from two perspectives. Both help you to determine what to plant and when to plant to get the best output from gardening.

A plant hardy zone map tells you how cold and hardy your respective zone plants are and how many frost-free days you get in a year.

On the other hand, heat zone tells you how heat tolerance your respective zone plants are and how many averages warm days temperatures over 30 Celsius you get in a year.

Some plants are cold tolerant, some are heat tolerant, and some can survive all year round. These zone map studies help you find suitable plants for your garden.

USDA plant hardiness zones and AHS heat zones

Here are the Details on the Hardiness Zones and Heat Zones Insights from the Infographic:

1. What is the USDA Plant Hardiness Zone?

If you intend to grow something in your yard, you need to know the USDA plant hardiness zones, planting zones, or gardening zones.

This is the critical task after deciding to start a garden. Every plant needs a suitable zone and environment to grow up and thrive. They recommend which plants grow best in a specific climate.

In the beginning, it would be a bit confusing, but it is easier than you think, and the practice field is the best place to learn plant hardiness zone.

So, carefully decide the hardiness zones for your garden.

There are now thirteen planting zones in the United States, according to the revised USDA hardiness zone map 2012.

These plant hardiness zones show the difference between the following zones. Each zone has a 10-degree differential and is divided into subzones A and B, separated by 5 degrees based on the average annual extreme minimum temperature.

Zone 1 is the most northern and coolest, and zone 13 is the most southern and hottest. Furthermore, subzone A is cooler than subzone B.

Suppose your garden is located at the northern border of the USDA hardy zone. In that case, you can grow several plants from the previous location.

On the other hand, if your garden is located on the southern border of the USDA plant zone, you can probably grow some plants from the next hardy zone.

2. Reasons to Know Your Planting Zone

Studying the planting zones helps you understand the opportunities and threats for your specific locations. There are plenty of reasons out there to know your planting zone. Here are the top reasons.

Buying the Correct Item:

When you invest in seeds or plants, you must be concerned about the return on your investment.

Most seed packets give you the information (such as heirloom or hybrid, maturity date, size, hardiness zone, heat zone, etc.) of the specific item when you buy them from the seed market.

For example, if you choose to buy tomato seeds, you need to consider the following factors:

  • First, some days to mature and harvest the plants.
  • Second, you get several frost-free days around the year (Following the USDA Hardiness Zone Map).
  • Third, you get many heat days around the year when the average temperature is over 86° Fahrenheit or 30°Celsius (Following the AHS Heat Zone Map).
  • Average nighttime temperature.
  • Survival ability in unstable weather conditions.

On the other hand, if you collect plants from nurseries, they always label their plants by planting zones. But it would help if you verified before you buy anything from the nursery.

Protecting Plants:

Studying planting zones can protect your plants from unexpected damage and save money, time, and labor. In addition, following their basic guidelines for planting time can give you a better harvest.

Planting zones tell you whether the plant you select for your garden is suitable or not.

Taking Good Care of Your Plants:

Based on the climate of your specific zone, you need to have some special care for your plants.

Some zone plants need less water supply, and some need more. In addition, some zone plants need air protection or staking.

Warm zones create more extended seasons but invite different pests and insects. Moreover, some specific zones spread out some particular diseases.

Try Something New:

When you understand the planting zone, you will get the confidence to apply new ideas in your garden. Try different zones’ plant which best suits your location.

In addition, grow some native plants that can easily survive in your region. Native plants match your landscaping and have varieties of beautiful flowers, which attract wildlife to pollinate and thrive new plants.

Find out Native Plants Society in your area, and they will provide you with the source of plants and other information.

 3. Microclimate Effects

The microclimate is a unique climate with different atmospheric conditions inside an average, more significant atmosphere in that zone. Sometimes this can happen naturally, but there have some essential factors that affect microclimates.

Geographic Location:

Your garden land’s location and surroundings are essential to define your climate. For example, suppose your land is situated on the side of a ­­­mountain. In that case, it receives a certain amount of sunlight or rainfall exposure compared to plain land.

The angle of slope of your land and its facing also determine how much sunlight exposure it receives. And the influence of airflow, water supply, and drainage system on your site.

In the heavy rainfall area, a vertical slope causes soil erosion.


The soil structure of your land also determines the microclimate. For example, if the soil has a large portion of clay, it will preserve more moisture than sand. Besides, the ground, covered with plants or mulch, evaporates less moisture and heat.


A source of water like a lake, pond, stream, river, or other sources changes the temperature surrounding your garden location.


Vegetation covers the soil, protects it from direct sunlight, and holds the moisture of the ground, which controls the temperature. Moreover, it filters dust and other particles from the air and acts as a windbreak.

Artificial Structures:

Your house can play an essential role in microclimates. For example, it can protect your area from wind and balance temperature if your home is surrounded by big trees, high walls, high-rise buildings, or fences.

Similarly, if your garden surface and walkways are covered with rocks or pavement, they can also moderate temperature.

If your garden has shade and shelter for your plants, a greenhouse might affect the microclimates in your location.

Besides, suppose you have a rooftop garden in an urban area. In that case, you should also consider the high-rise buildings surrounding the roof, sunlight exposure, airflow, water supply, and other factors.

4. What Plants Grow Well in My Area?

New gardeners need help choosing the right plant because of the puzzle of the hardy zone. So which plants grow well in your area is a burning question.

The USDA plant hardiness zone map gives you a basic idea about planting zones, how many frost-free days you will get for cultivation, and planting time.

However, it only gives you some instructions on what to do next after selecting the planting time for your garden.

You can go to your nearest local garden center or neighbor and ask which plants they suggest growing in your garden. If your garden is located in a microclimate zone, you will get some favor or face challenges.

Besides, the seed packets have proper instructions and guidelines for planting seeds and hardiness zone. They can help you to decide which plants to grow in your area.

Most of the local nurseries label their plants according to the planting zones. Therefore, this can be an excellent source for selecting plants.

If you wish to start a container or raised bed garden outside, you should pick plants that are a hardy minimum of two zones lower than the zone you live in. It’s because containers and raised beds are cooler than the ground level.

For example, if you are in zone 6, pick some plants from zone 4 or lower for your outside container or raised bed garden.

On the other hand, if you are in zone 4, you can lift your hardiness zone to zone 6 or 7 by using a greenhouse or clear plastic cold-resistant frame.

5. Limitations of the Hardiness Zone Map:

A planting zone introduces you to the time frame of cultivation, average extreme minimum temperature, and the climate of a specific region, but it doesn’t cover everything.

Some other significant factors influence your gardening.

Unpredicted Weather:

Weather is an essential factor in gardening. However, the hardiness zone only shows you the average data of a specific climate, and climate calculates the last 25 years’ data of higher and lower temperatures and other factors of a particular zone.

But, your garden plants are affected by the unpredicted weather pattern of the current season. The weather only matches the hardiness zone map sometimes. Vegetables and herbs gardening mainly depends on the temperature your garden belongs to during that time.

Soil Health:

Planting zones show a specific zone’s average higher and lower temperature data. But they don’t tell about the soil health of your garden location.

No matter your garden zone, soil health is essential in gardening. Therefore, you must check your garden soil nutrients with a soil test kit before the start.

Besides, it would help if you considered your location’s rainwater ratio, humidity, and proper drainage system.

Pests and Diseases:

The hardiness zone gives you the idea of the last and first frost date and the average minimum temperature of a growing season. But it doesn’t help you to control pests and diseases.

6. What is the Plant Heat Zone Map?

Heat zone map helps to determine the suitable heat tolerant plants which can survive in your respective zone where the average temperature is over 86° Fahrenheit or 30°Celsius.

7. Why Does Above 86° Fahrenheit Temperature Matter in Gardening?

Some cold-hardy plants cannot take overheat and become damaged. Heat zone map selects plants that can thrive in your garden all year round.

When you buy seed packets from the market or plants from the nursery, you may notice two sets of numbers. The first set indicates extreme and minimum hardiness zone, and the second set indicates maximum and minimum heat zone for particular plants.

For example, if the seed packet or plant tag indicates numbers like 7-9, 9-7, the particular plant can survive between USDA hardy zone 7-9. And the second set of numbers indicates the plant is suitable for AHS heat zone 9-7.

Therefore, this heat zone map would be an ideal guideline for gardeners regarding which plants can survive in a particular heat zone.

8. How Does the Heat Zone Map Work?

The USDA Plant hardiness zone map is the well-known and most popular way to determine plants that can survive in winter cold and thrive over the year.

But you cannot determine plants using the hardy zone map during drought season. It would help if you considered other factors to choose the right plants for your garden.

Therefore, the American Horticultural Society first introduced the AHS plant heat zone map, divided into 12 heat zones. This heat zone map calculates the average number of heat days over 86° Fahrenheit each year.

Reaching the temperature at that point can cause physical damage to the plants from heat.

Over 15000 plants coded heat tolerance for the time being, which can withstand cold weather and tolerate overheating. This heat zone map makes the job easier to select the suitable plants for your specific garden location.


Hardiness and heat zone maps are the basic guidelines for selecting plants but don’t let them limit you. Instead, you better study the zone maps deeply to understand and apply them to innovate something new.

It would be best if you mentioned that, no matter what your zone maps, plant tags, or other statistics say about your location, you couldn’t get it 100% accurate. There still have some hope if your research finds a negative result.

Start small to reduce the risk and understand the exact situation. You may face some unique problems or get some exceptional opportunities and solutions to the issues that nobody can explain about the particular location you live in.

Wish your gardening journey will be innovative and adventurous.

Sources and Citations:

John Michael
John Michael is a self-help writer and a hobby gardener. Michael’s passion in writing is to inspire the beginner gardeners to not just “hang in there” or “make it through” but to thrive. He does this through blogging.

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