What Plant Hardiness Zones DON'T Tell You.
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Date: 2022-07-18
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Comments and reviews: 15
Paul
Good video. Good info. and intuition. I've been thinking on the same lines. My USDA hardiness zone is 9b. I grew up gardening in Hardiness Zone 6b. The USDA zones were good. They worked. Now that I'm here, they are useless. The city I live in is a micro-climate which does not in anyway confirm to USDA categories. Zone 9b is supposed to have hot summers. It is rare for the temperature here to exceed 63 degrees F. On the converse, the USDA Hardiness map works for the lows. Temperatures rarely drop below 36 degrees F. But, they did drop to 34 degrees two days ago, on April 16. I have began to use a combination of USDA zones with geography definitions such as Mediterranean Climate, Maritime Climate, Temperate Rain Forest, and etc. This has yielded a slightly more exact approximation of my climate zone. In the past, I wouldn't have needed this information, but as our family has been seeking to create a self-sustaining, permaculture garden, within space and environmental constraints, I have been looking at unfamiliar crops. To make things more complicated, our climate seems to be changing. The temperature actually got up to 73 degrees last year. My kids were complaining about the heat? The winter time lows dipped down to freezing more frequently, while staying above 27- 29 degrees (normal limits. And, though we supposedly live in a Mediterranean Climate there was no rain this winter. However, it's been raining cats and dogs this spring. It's like I'm back in Zone 6b again: totally atypical. Thanks,
again. I thought I would offer this for food for thought.
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Good video. Good info. and intuition. I've been thinking on the same lines. My USDA hardiness zone is 9b. I grew up gardening in Hardiness Zone 6b. The USDA zones were good. They worked. Now that I'm here, they are useless. The city I live in is a micro-climate which does not in anyway confirm to USDA categories. Zone 9b is supposed to have hot summers. It is rare for the temperature here to exceed 63 degrees F. On the converse, the USDA Hardiness map works for the lows. Temperatures rarely drop below 36 degrees F. But, they did drop to 34 degrees two days ago, on April 16. I have began to use a combination of USDA zones with geography definitions such as Mediterranean Climate, Maritime Climate, Temperate Rain Forest, and etc. This has yielded a slightly more exact approximation of my climate zone. In the past, I wouldn't have needed this information, but as our family has been seeking to create a self-sustaining, permaculture garden, within space and environmental constraints, I have been looking at unfamiliar crops. To make things more complicated, our climate seems to be changing. The temperature actually got up to 73 degrees last year. My kids were complaining about the heat? The winter time lows dipped down to freezing more frequently, while staying above 27- 29 degrees (normal limits. And, though we supposedly live in a Mediterranean Climate there was no rain this winter. However, it's been raining cats and dogs this spring. It's like I'm back in Zone 6b again: totally atypical. Thanks,
again. I thought I would offer this for food for thought.
reply
cameron
Meteorologist and plant nerd wannabe here. There is another rather large weakness of the hardiness zones. As you mentioned, it is based off the typical coldest temperature of the season. This temperature is based off a 30 year average. Take the the coldest temperature of each year over the last 30 years, add them together, and divide by 30. Nice simple math. Problem, it doesn't take into account the year to year variability. In San Diego, your annual minimum likely doesn't vary as much as it does in some other places. For most places east of the Rockies, the annual minimum typically varies quite a bit from year to year. I live in southeastern Houston. I'm simultaneously close to the urban heat core and the bay. My zone is 9B which equates to an annual minimum of 25-29F. The airport nearby averages an annual low of 28F. But in the 8 winters I have lived here 2 never froze, 3 never dipped below 30F, one dropped to 23F, and two dropped into the teens. Our annual minimum over 8 years has ranged from 15F to 36F. Another way to put it is we have had 5 winters in zone 10, 1 in zone 9, and two in zone 8. Where my mom lives in the North Carolina foothills is really similar. Her annual low average in the lower teens. But in the last decade, they have been as low as 1F while also having a winter that didn't dip below 25F.
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Meteorologist and plant nerd wannabe here. There is another rather large weakness of the hardiness zones. As you mentioned, it is based off the typical coldest temperature of the season. This temperature is based off a 30 year average. Take the the coldest temperature of each year over the last 30 years, add them together, and divide by 30. Nice simple math. Problem, it doesn't take into account the year to year variability. In San Diego, your annual minimum likely doesn't vary as much as it does in some other places. For most places east of the Rockies, the annual minimum typically varies quite a bit from year to year. I live in southeastern Houston. I'm simultaneously close to the urban heat core and the bay. My zone is 9B which equates to an annual minimum of 25-29F. The airport nearby averages an annual low of 28F. But in the 8 winters I have lived here 2 never froze, 3 never dipped below 30F, one dropped to 23F, and two dropped into the teens. Our annual minimum over 8 years has ranged from 15F to 36F. Another way to put it is we have had 5 winters in zone 10, 1 in zone 9, and two in zone 8. Where my mom lives in the North Carolina foothills is really similar. Her annual low average in the lower teens. But in the last decade, they have been as low as 1F while also having a winter that didn't dip below 25F.
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Julie
Unfortunately, with permanent plants like trees, shrubs and perennials, that average cold would possibly mean that every so often, when you have a not so average cold blast, you may lose some plants that may be the bones of your garden/landscape.
I've also been wondering, if you have some tender plants in a greenhouse, and the low temp you might get a few hours comes a few degrees below what a plant or 2 can deal with outdoors, exposed to wind or rain, would that plant be able to handle that few degrees below the recommended lowest temperature?
It would be above freezing though. To be specific, a zone 10b hardy plant being in a greenhouse 42f.
My greenhouse is now 42f, and I am leery of going out to put on my backup heater because it's in the teens outside, and it's gonna be icy and I don't want to fall and bust my butt going to the GH.
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Unfortunately, with permanent plants like trees, shrubs and perennials, that average cold would possibly mean that every so often, when you have a not so average cold blast, you may lose some plants that may be the bones of your garden/landscape.
I've also been wondering, if you have some tender plants in a greenhouse, and the low temp you might get a few hours comes a few degrees below what a plant or 2 can deal with outdoors, exposed to wind or rain, would that plant be able to handle that few degrees below the recommended lowest temperature?
It would be above freezing though. To be specific, a zone 10b hardy plant being in a greenhouse 42f.
My greenhouse is now 42f, and I am leery of going out to put on my backup heater because it's in the teens outside, and it's gonna be icy and I don't want to fall and bust my butt going to the GH.
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George
The hardiness zones always confused me. I look at the record highs and lows as well as the average temps for each month for the past few years. Ill compare that to what the farmers almanac tells me for my zip code as well as Weather Undergrounds 7 day forecast (they predict polar vortexes very well. My goal is to predict when the lows are going to be 46f+ and when highs get over 98f. Until the lows reach 46f, Ill take my seedlings outside everyday and bring them inside every night. Once Im positive the lows are above 46f, Ill transplant the seedlings outside. The plants that dont like extreme heat and sunlight get put into potting bags so I can move them into the shade of the porch on those days when the highs hit 98f.
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The hardiness zones always confused me. I look at the record highs and lows as well as the average temps for each month for the past few years. Ill compare that to what the farmers almanac tells me for my zip code as well as Weather Undergrounds 7 day forecast (they predict polar vortexes very well. My goal is to predict when the lows are going to be 46f+ and when highs get over 98f. Until the lows reach 46f, Ill take my seedlings outside everyday and bring them inside every night. Once Im positive the lows are above 46f, Ill transplant the seedlings outside. The plants that dont like extreme heat and sunlight get put into potting bags so I can move them into the shade of the porch on those days when the highs hit 98f.
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Bob
The Western Garden book is not perfect. But its really good at addressing smaller zones. I worked for a large California Nursery that specialized in deciduous Fruit and shade trees outside Visalia California. I set up a program for selling deciduous fruit trees by microclimate. Because stone fruits, apples, Cherries, Pears and Nut Trees and other deciduous fruit trees rely on Chilling Hours (hours under 45 degrees Fahrenheit.
I put a TON of work into that. Basically informing each Nursery by Microclimate. So people wouldnt buy the inappropriate variety. VERY complex. And my boss just let it die. Didnt want to pay for Graphics the consumer could understand. Oh well, I did get paid to do the research.
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The Western Garden book is not perfect. But its really good at addressing smaller zones. I worked for a large California Nursery that specialized in deciduous Fruit and shade trees outside Visalia California. I set up a program for selling deciduous fruit trees by microclimate. Because stone fruits, apples, Cherries, Pears and Nut Trees and other deciduous fruit trees rely on Chilling Hours (hours under 45 degrees Fahrenheit.
I put a TON of work into that. Basically informing each Nursery by Microclimate. So people wouldnt buy the inappropriate variety. VERY complex. And my boss just let it die. Didnt want to pay for Graphics the consumer could understand. Oh well, I did get paid to do the research.
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Tara
Im in a Zone 4 (Alaska)- and I can say that our climate and seasons have changed a lot over the past 20 years. And even year to year. This year we still have snow several weeks later than we did last year. We also have such a short growing season but very long daylight hours. So we have the capacity to grow certain crops that a shorter day Zone 4 cannot. Zone 4 is a challenge. But its not hopeless. You just have to work with what youve got. Root vegetables/potatoes, pumpkins and most squash, leafy greens, cabbage and berries do exceptionally well without a greenhouse. Most things that are slow to mature, not so much. We grow record breaking pumpkins and cabbage in Alaska. its a whole thing. Haha
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Im in a Zone 4 (Alaska)- and I can say that our climate and seasons have changed a lot over the past 20 years. And even year to year. This year we still have snow several weeks later than we did last year. We also have such a short growing season but very long daylight hours. So we have the capacity to grow certain crops that a shorter day Zone 4 cannot. Zone 4 is a challenge. But its not hopeless. You just have to work with what youve got. Root vegetables/potatoes, pumpkins and most squash, leafy greens, cabbage and berries do exceptionally well without a greenhouse. Most things that are slow to mature, not so much. We grow record breaking pumpkins and cabbage in Alaska. its a whole thing. Haha
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Alyce
This is helpful. I have a house in Joshua trees which is a zone 9 and in desert hot springs (palm springs) which is also a zone 9. It freezes and shows sometimes in JT but never in DHS. I didnt understand how they were both zone 9! In DHS the summers can be over 120/100 but in winter it averages about 60/40. I was thinking it is a zone 10. Also there is more rain in DHS than JT so it is more humid (especially with all the golf courses. So I think Im going to go with zone 10 from now on.
Im just starting and I was going threw a lot of plants. Luckily most I started from seeds I saved from my corner produce stand and the woman there helps me with tips on how to grow stuff.
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This is helpful. I have a house in Joshua trees which is a zone 9 and in desert hot springs (palm springs) which is also a zone 9. It freezes and shows sometimes in JT but never in DHS. I didnt understand how they were both zone 9! In DHS the summers can be over 120/100 but in winter it averages about 60/40. I was thinking it is a zone 10. Also there is more rain in DHS than JT so it is more humid (especially with all the golf courses. So I think Im going to go with zone 10 from now on.
Im just starting and I was going threw a lot of plants. Luckily most I started from seeds I saved from my corner produce stand and the woman there helps me with tips on how to grow stuff.
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The
Thank You! For the easy explanation on this. It's very confusing for me living in the Pacific Northwest, just south of Seattle our weather is pretty mild, with a cool temperate climate. Lot's of overcast, rainy or sprinkly days in Spring, and fall. July - Thru Sept. even Oct. pretty nice 70's maybe 80's. And yet according to the Grow Zone we are the same zone as FLORIDA. Not even close. I remember watching a video on someone in my same zone HARVESTING Zucchini in MAY as I was just planting them! I tend to think my grow zone is more like Gary's from 'The rusted Garden' 7, Which he mentioned that YOU are doing the tomato contest with him this year. Good luck!
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Thank You! For the easy explanation on this. It's very confusing for me living in the Pacific Northwest, just south of Seattle our weather is pretty mild, with a cool temperate climate. Lot's of overcast, rainy or sprinkly days in Spring, and fall. July - Thru Sept. even Oct. pretty nice 70's maybe 80's. And yet according to the Grow Zone we are the same zone as FLORIDA. Not even close. I remember watching a video on someone in my same zone HARVESTING Zucchini in MAY as I was just planting them! I tend to think my grow zone is more like Gary's from 'The rusted Garden' 7, Which he mentioned that YOU are doing the tomato contest with him this year. Good luck!
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Bobbun
Not mentioned here as a consideration: the relationship between day length and first/last frost date. Consider this specific application: I'm planning on planting some roselle this year, and I live in zone 7a. The growing season is definitely long enough to grow it, but because it's a short day flowering tropical plant, no matter how much the plants have matured it won't start flowing until pretty close to my first frost date, which will kill it. This crop should be doable, but I'll definitely have to resort to some combination of covering the plants for darkness and polytunnels for warmth to make it work.
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Not mentioned here as a consideration: the relationship between day length and first/last frost date. Consider this specific application: I'm planning on planting some roselle this year, and I live in zone 7a. The growing season is definitely long enough to grow it, but because it's a short day flowering tropical plant, no matter how much the plants have matured it won't start flowing until pretty close to my first frost date, which will kill it. This crop should be doable, but I'll definitely have to resort to some combination of covering the plants for darkness and polytunnels for warmth to make it work.
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Uranus
We use the USDA zones in Europe as well. They are actually very helpful for a first look, or for beginners. Also as a gardener in the mildest parts of Germany I can explain to ordinary people, why I'm able to grow palm trees and exotic plants with little to no protection and others in Germany might not.
But my tip is always: When you want to plant something, research the original habitat and distribution of the plant. This works very well. And then just risk it! I've often grown stuff, that wasn't supposed to cope well with my climate but did amazing.
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We use the USDA zones in Europe as well. They are actually very helpful for a first look, or for beginners. Also as a gardener in the mildest parts of Germany I can explain to ordinary people, why I'm able to grow palm trees and exotic plants with little to no protection and others in Germany might not.
But my tip is always: When you want to plant something, research the original habitat and distribution of the plant. This works very well. And then just risk it! I've often grown stuff, that wasn't supposed to cope well with my climate but did amazing.
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Cristia
I'm in a zone 10 microclimate pocket caused by our city being at the edge of the Sierra foothills (cold air rolls down into the valley, surround by zone 9. My yard has never had frost in the 6 years I've lived here, and my neighbors grow avocados, but my parents across town get black ice on their street if it rains in January.
Thing is, because it still does get cold, just not quite freezing, at the same time as the rest of the valley, I still get about 700 chill hours.
End result: I can grow both a mango tree and a cherry tree in my yard.
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I'm in a zone 10 microclimate pocket caused by our city being at the edge of the Sierra foothills (cold air rolls down into the valley, surround by zone 9. My yard has never had frost in the 6 years I've lived here, and my neighbors grow avocados, but my parents across town get black ice on their street if it rains in January.
Thing is, because it still does get cold, just not quite freezing, at the same time as the rest of the valley, I still get about 700 chill hours.
End result: I can grow both a mango tree and a cherry tree in my yard.
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Sylvie
I'm in zone 6a and we are trying to grow lemon trees in the pot because it getts to cold for them in the winter so we have to bring them inside and we bring them out in the warmer months. I'm in massachusetts so average highs are in the low 80s and we a higher humidity throughout the year. We also gonna try yot plant a native plant known as the Beach Plum or Prunus Maritima. Because they are around here mostly on the coast we will be able to plant it and it can stay outside all year round. Can't wait to get beach plums so I can make jam out of them
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I'm in zone 6a and we are trying to grow lemon trees in the pot because it getts to cold for them in the winter so we have to bring them inside and we bring them out in the warmer months. I'm in massachusetts so average highs are in the low 80s and we a higher humidity throughout the year. We also gonna try yot plant a native plant known as the Beach Plum or Prunus Maritima. Because they are around here mostly on the coast we will be able to plant it and it can stay outside all year round. Can't wait to get beach plums so I can make jam out of them
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Peter
Just found this April 2021. Very good video Mahalo. Long time zone 5 Gardner NE Rural Illinois, Moved to Maui, HI just restarting, You talk about micro climates this place is the king of them. Just go up 100 ft. vertical and the game changes. Wind direction can make the temp swing 20 degF on the high side. Then you take into the account of the length of day changes all sorts of new challenges. Old went from 11 hr. to 17 hr. daylight and new goes from 12 to 13 hr. daylight length. I'm an old dog (69) trying to learn new tricks.
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Just found this April 2021. Very good video Mahalo. Long time zone 5 Gardner NE Rural Illinois, Moved to Maui, HI just restarting, You talk about micro climates this place is the king of them. Just go up 100 ft. vertical and the game changes. Wind direction can make the temp swing 20 degF on the high side. Then you take into the account of the length of day changes all sorts of new challenges. Old went from 11 hr. to 17 hr. daylight and new goes from 12 to 13 hr. daylight length. I'm an old dog (69) trying to learn new tricks.
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Jody
Zone 10B in Florida means we can only grow Florida vegg, its too hot for greens without a filter, its too cold for tropical, we get no frost so no winter vegg will grow and were too humid for mediterranean plants to grow without constant babysitting. Were big on monoculture. If you want lots of rice or big sugar weve got you covered! I would love to grow sweet corn or sweet grapes or beets! Nope! Im looking into Asian options. They have weather like ours and Im considering using a zone manipulation to grow some tropical fruits.
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Zone 10B in Florida means we can only grow Florida vegg, its too hot for greens without a filter, its too cold for tropical, we get no frost so no winter vegg will grow and were too humid for mediterranean plants to grow without constant babysitting. Were big on monoculture. If you want lots of rice or big sugar weve got you covered! I would love to grow sweet corn or sweet grapes or beets! Nope! Im looking into Asian options. They have weather like ours and Im considering using a zone manipulation to grow some tropical fruits.
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Bolshevik
The Canadian Hardiness Zones are better as they are determined via an equation that takes into account the average minimum temperature of the coldest month, the average number of frost-free days, the average total precipitation between the months of June and November (switch that to December and May for the Southern Hemisphere, the average maximum temperature of the warmest month, the average snow depth at its deepest and the strongest gust of the last thirty years.
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The Canadian Hardiness Zones are better as they are determined via an equation that takes into account the average minimum temperature of the coldest month, the average number of frost-free days, the average total precipitation between the months of June and November (switch that to December and May for the Southern Hemisphere, the average maximum temperature of the warmest month, the average snow depth at its deepest and the strongest gust of the last thirty years.
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