Heat Zones Map and USDA Plant Hardiness Zones confusio
Apr 23, 2023 7:00:51 GMT -5
datgirl, gardendmpls, and 1 more like this
Post by raphanus on Apr 23, 2023 7:00:51 GMT -5
I was very happy to see that the American Hort Society finally made a Heat Zones Map to compliment the USDA [cold] Hardiness Zones Map!
I see a lot of gardeners on social media like Facebook garden groups and occasionally meet people in person who misinterpret the USDA [cold] Hardiness Zones classifications.
Sometimes people will ask me questions that don’t make sense like “When do I plant tomatoes in Zone 7?” or “What can I plant in Zone 5b in April?” etc.
Traditional USDA [cold] Hardiness Zone numbers unfortunately don’t help with summer garden planning.
The USDA Zone numbers tell you what you can expect for winter extreme minimum temperatures, that’s it.
USDA [cold] Hardiness Zone numbers do not tell you when your first frost or last frost will be.
They do not tell you how long your winters will be.
They do not tell you how hot your summers will be.
They do not tell you when to sow seeds or when to transplant.
They tell you how cold your winters can get.
Emphasis on can. USDA Zones tell you average winter *extreme* minimums. They look at decades of weather data and see what the coldest days were each winter and take the average of those. Where I live, we have a lot of 80 degree days in December and February and people think they can grow mangoes, but because we get a couple nights in January where it drops down to 25 F, we are still Zone 8.
USDA [cold] Hardness Zone numbers are helpful for choosing perennials like fruit trees and helpful for planning late fall/ winter vegetables.
For example, if you are in Zone 8 or above, you can plant citrus trees because your winters are fairly mild. If you are in zone 10 or above, you can plant avocados and papayas because your winters are nearly frost-free. If you are zone 6 or above, you can probably grow spinach and carrots and lettuce and kale all winter long without much protection.
Different parts of the country can have the same USDA zone number but have incredibly different summer weather. Seattle area has some Zone 8 and North Florida has some Zone 8, but their summers are very different from each other.
Parts of Hawaii are Zone 12 and 13, but their summers are much cooler than parts of North Carolina that are Zone 7 or 8. There are places in the upper Midwest that are Zone 5, but see 100 degree temperatures in July and August.
USDA zone numbers only tell you what to expect for extreme winter minimums, that’s it.
Fortunately, there are now also Heat Zones that can help new gardeners plan for summer!
It’s still critical to know your first and last frost dates, but knowing your Heat Zone can help you plan your spring and summer gardens. Heat zones can help you decide how late into spring you can plant peas and beans and potatoes and tomatoes and other crops that don’t like hot weather.
If your summers are fairly cool, you may be able to grow peas and beans and potatoes and tomatoes and brassicas and root crops all summer long. But if you live in a high heat zone, you may have to replace all of your spring crops with more heat-tolerant crops like okra, sweetpotato, eggplant, cowpeas, watermelon, and peppers by May. If you live in a low heat zone, you may not be able to grow okra or sweetpotato or watermelon at all because these crops need very hot weather to really thrive.
Know your USDA [cold] Hardiness Zone to help you decide which perennials you can plant and which fall crops you can overwinter, but know your Heat Zone to help you decide which crops to grow in late spring and summer. Know your first and last frost dates to decide when to plant.
I see a lot of gardeners on social media like Facebook garden groups and occasionally meet people in person who misinterpret the USDA [cold] Hardiness Zones classifications.
Sometimes people will ask me questions that don’t make sense like “When do I plant tomatoes in Zone 7?” or “What can I plant in Zone 5b in April?” etc.
Traditional USDA [cold] Hardiness Zone numbers unfortunately don’t help with summer garden planning.
The USDA Zone numbers tell you what you can expect for winter extreme minimum temperatures, that’s it.
USDA [cold] Hardiness Zone numbers do not tell you when your first frost or last frost will be.
They do not tell you how long your winters will be.
They do not tell you how hot your summers will be.
They do not tell you when to sow seeds or when to transplant.
They tell you how cold your winters can get.
Emphasis on can. USDA Zones tell you average winter *extreme* minimums. They look at decades of weather data and see what the coldest days were each winter and take the average of those. Where I live, we have a lot of 80 degree days in December and February and people think they can grow mangoes, but because we get a couple nights in January where it drops down to 25 F, we are still Zone 8.
USDA [cold] Hardness Zone numbers are helpful for choosing perennials like fruit trees and helpful for planning late fall/ winter vegetables.
For example, if you are in Zone 8 or above, you can plant citrus trees because your winters are fairly mild. If you are in zone 10 or above, you can plant avocados and papayas because your winters are nearly frost-free. If you are zone 6 or above, you can probably grow spinach and carrots and lettuce and kale all winter long without much protection.
Different parts of the country can have the same USDA zone number but have incredibly different summer weather. Seattle area has some Zone 8 and North Florida has some Zone 8, but their summers are very different from each other.
Parts of Hawaii are Zone 12 and 13, but their summers are much cooler than parts of North Carolina that are Zone 7 or 8. There are places in the upper Midwest that are Zone 5, but see 100 degree temperatures in July and August.
USDA zone numbers only tell you what to expect for extreme winter minimums, that’s it.
Fortunately, there are now also Heat Zones that can help new gardeners plan for summer!
It’s still critical to know your first and last frost dates, but knowing your Heat Zone can help you plan your spring and summer gardens. Heat zones can help you decide how late into spring you can plant peas and beans and potatoes and tomatoes and other crops that don’t like hot weather.
If your summers are fairly cool, you may be able to grow peas and beans and potatoes and tomatoes and brassicas and root crops all summer long. But if you live in a high heat zone, you may have to replace all of your spring crops with more heat-tolerant crops like okra, sweetpotato, eggplant, cowpeas, watermelon, and peppers by May. If you live in a low heat zone, you may not be able to grow okra or sweetpotato or watermelon at all because these crops need very hot weather to really thrive.
Know your USDA [cold] Hardiness Zone to help you decide which perennials you can plant and which fall crops you can overwinter, but know your Heat Zone to help you decide which crops to grow in late spring and summer. Know your first and last frost dates to decide when to plant.
