Why Should I Learn Plant Hardiness Zones and Heat Zones?

Hardiness zone and heat zone map tell you the same thing from two different perspectives. Both help you to determine what to plant and when to plant? for getting the best output of gardening.

Hardy zone map tells you how cold hardiness 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 average warm days temperature over 30 Celsius you get in a year.

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

Hardiness zone infographic, heat zone  infographic

Here’s the details on the hardiness zones and heat zones insights from the infographic:

1. What is a plant hardiness zone?

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

This is the key 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 little bit confusing, but it is not as difficult as you think and the practice field is the best place to learn plant hardiness zone.

So, decide carefully 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 next zones, and each zone has a 10-degree differential, and 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 as well as zone 13 is the most southern and hottest. Furthermore, subzone A is cooler than subzone B.

If your garden located at the northern border of USDA hardy zone, you can grow a number of plants from the previous zone.

On the other hand, if your garden 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 help you to understand the opportunities with threats for your specific locations. There are plenty of reasons out there to know your planting zone. Here are the top reasons.

Buying the right item:

When you invest in seeds or plants, you must have to concern about the return of your investment.

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

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

  • A number of days to mature and harvest the plants.
  • A number of frost-free days you get around the year (Following the USDA Hardiness Zone Map).
  • A number of heat days you get around the year when the average temperature over 86° Fahrenheit or 30°Celsius (Following the AHS Heat Zone Map).
  • Average nighttime temperature.
  • Survival ability in the uneven weather condition.

On the other hand, if you collect plants from the nurseries, they always label their plants by planting zones. But you need to verify before you buy anything from the nursery.

Protecting plants:

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

Planting zones tell you 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. Some zone plants need air protection or staking.

Warm zones create longer season but they 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 zone’s plant which best suits in your location.

In addition, grow some native plants which can easily survive in your region. Native plants match with 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:

Microclimate is a unique climate which has different atmospheric conditions inside an average larger climate in that zone. Sometimes this can happen naturally, but there have some major factors that affect microclimates.

Geographic location: 

The location of your garden land and its surroundings is really important to define your climate. If your land is situated on the side of a ­­­mountain it receives a certain amount of sunlight or rainfall exposure compared to a plain land.

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

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


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


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


Vegetation covers the soil and protects it from direct sunlight as well as hold the moisture of the soil, 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 important role in microclimates. If your house surrounded by big trees, high walls, high rise buildings or fences, it can protect your area from wind and balance temperature.

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

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

Besides, if you have a rooftop garden in urban areas, you should also take into consideration 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 face some troubles to choose the right plant because of the puzzle of the hardy zone. So which plants grow well in your area is a burning question.

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 does not give you an exact instruction what to do next after selecting the planting time for your garden.

You can go to your nearest local garden center or neighbor and talk to them, which plants they suggest to grow in your garden. If your garden located in a microclimate zone you will get some favor or face some 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 a nice source for selecting plants.

If you wish to start a container or raised bed garden outside, you should pick the plants, which are hardy minimum 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 also lift up 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:

Planting zone introduces you the time frame of cultivation, average extreme minimum temperature, and the climate of a specific region but doesn’t cover all things.

There are some other major factors influences your gardening.

Unpredicted weather:

Weather is an important factor in gardening. Hardiness zone only shows you the average data of a specific climate and climate calculates last 25 years data of higher and lower temperature and other factors of a specific zone.

But, your garden plants affected by the unpredicted weather pattern of the current season. Weather doesn’t match the hardiness zone map all the time. Vegetables and herbs gardening mainly depends on the weather your garden belongs during that time.

Soil health:

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

No matter what is your garden zone, soil health is one of the important factors of gardening. You must check your garden soil nutrients with soil test kit before the start.

Besides, you should consider the rainwater ratio, humidity and proper drainage system in your location.

Pests and diseases:

Hardiness zone gives you the idea of last and first frost date and the average minimum temperature of a growing season. But it doesn’t help you to control pest 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 over 86° Fahrenheit or 30°Celsius.


7. Why above 86° Fahrenheit temperature matters in gardening?

Some cold-hardy plants cannot take overheat and become damaged. Heat zone map selects plant 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 the particular plants.

For example, if the seed packet or plant tag indicate numbers like 7-9, 9-7; that means the particular plant can survive in-between USDA hardy zone 7-9, as well as the second set of numbers, indicate the plant is suitable for AHS heat zone 9-7.

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


8. How does heat zone map work?

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

But you cannot determine plants using the hardy zone map during the season of drought. You need to consider some other factors to choose the right plants for your garden.

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

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

There are over 15000 plants coded heat tolerance for the time being, which can withstand in cold weather and tolerant the overheat. 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. You better study the zone maps deeply to understand and apply them to innovate something new.

Need to mention that, no matter what your zone maps or plant tags and other statistics say about your location, you couldn’t get it 100% accurate. There still have some hope if your research found a negative result.

Start small to reduce the risk and understand the exact situation. You may face some unique problems or get some special opportunities and solutions against the problems 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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