The USDA Plant Hardiness Zone Map is a tool used by gardeners and growers to determine which perennial plants are most likely to thrive in specific regions. The map divides North America into 11 hardiness zones, with Zone 1 being the coldest and Zone 11 being the warmest. These zones are based on the average lowest temperatures of each region of the US.
The USDA Plant Hardiness Zone Map helps gardeners identify the plants that tolerate their climate and provide a guide to the best growing conditions. The 2023 map is based on 30-year averages of the lowest annual winter temperatures at specific locations and is divided into 10-degree Fahrenheit zones.
Growing in greenhouses offers an optimal environment for year-round vegetable and fruit cultivation in zones 7 to 9, offering an optimal environment for year-round vegetable and fruit cultivation. In the UK, Zone 8 allows for an early start in late winter, typically February, while Zone 7 in the milder southern regions, March, can be grown in Zone 6.
To grow anything in Zone 6 in a greenhouse, keep the temperature regulated and consider additional grow conditions. The USDA’s hardiness zones begin with Zone 1, which is the coldest, and end with Zone 13, which encompasses the warmest growing areas. By understanding the hardiness of plants and using the USDA Plant Hardiness Zone Map, gardeners can find the best plants for their specific climate and preferences.
📹 The NEW Hardiness Zone Map (Explained)
There’s a new Plant Hardiness Zone map from the USDA. About half of U.S. gardeners are now in a new zone. The 2023 map is …
What is the temperature regulation in greenhouses?
Install roof and wall vents in your greenhouse to ensure good ventilation. Use pockets in a high tunnel system to vent hot air, allowing cool, fresh air to enter. Opt for a wet wall method, which pumps water through the wall and cools evaporated water with a fan. Monitor humidity levels and cut off water supply when moisture rises. The greenhouse’s temperature can rise to 100 degrees Fahrenheit on hot days and equalize with outdoor settings on winter evenings, causing a chilly atmosphere. Ensure that the greenhouse is well-ventilated and that humidity levels are monitored.
Will an unheated greenhouse protect from frost?
Keeping your greenhouse unheated during autumn and winter is crucial for maintaining frost-free plants and growing hardy crops like salads and herbs. Unheated greenhouses can keep overnight temperatures up to 5°C warmer than outside, ensuring plants stay dry and frost-free. This helps plants survive by reducing the likelihood of freezing. To keep your greenhouse in top condition, consider using greenhouse accessories and a guide on the best pressure washers.
Ensure your plants get plenty of light, as natural light levels are low in winter. Remove any shading material and clean the glass to maximize available light. This will help keep your greenhouse in top condition and ensure the survival of your plants.
What is the best temperature for plants in a greenhouse?
Most common greenhouse crops require a temperature range of 18-24°C (64°F – 75°F) for optimal growth and quality. Temperatures outside this range can lead to slower growth and suboptimal crop quality. Controlling humidity is essential in greenhouses and indoor growing facilities to prevent problems and inefficiencies. Untreated humidity can cause crops to grow slower, smaller, and reduce their quality. Therefore, growers rarely stray from optimal greenhouse temperatures.
Can you grow plants in a greenhouse in the winter?
Winter is a great time to grow plants in a greenhouse, as they can still thrive with some protection from the elements. While some crops may not grow as quickly as in warmer months, they can still thrive with proper planning. The type of greenhouse and location will determine the appropriate crops for your greenhouse, but some common crops work well for everyone. Here are some tips for growing herbs and vegetables in a greenhouse in winter, as well as tips for insulating and ventilating your greenhouse during colder months.
What is the lowest temperature for a greenhouse?
To maintain optimal plant growth, keep your greenhouse temperature below 3C (37F). Tender plants like pelargoniums, half-hardy fuchsias, and citrus trees prefer a minimum of 7C (45F), and safest at 10C (50F). This temperature is ideal for young plants and plug plants. If you have a conservatory, use it to overwinter delicate plants. Position heaters carefully, placing them in an open, central spot away from water and angling the heater to prevent foliage desiccation by direct airflow above nearby plants.
What is the cold temperature in a greenhouse?
To maintain a greenhouse, monitor conditions, regulate temperatures, and use appropriate heating systems. Use thermometers, thermostats, and heating mats to monitor and regulate horticultural temperatures. Use safe heat sources like radiant heaters, heating cables, or small space heaters on cold nights. Avoid propane or kerosene heaters to prevent carbon monoxide production. Maintain proper ventilation to prevent fungal diseases and use vents, exhaust fans, and cracked doors for air circulation. Place sensors throughout the greenhouse to track excessive humidity, with dehumidifiers or exhaust fans helping lower humidity levels.
What happens if greenhouse gets too cold?
Freezing injury is a condition where plants are exposed to temperatures below freezing, causing damage that is more noticeable after a day or two of warmer temperatures. This injury can occur at temperatures above freezing and as high as 54° F. Common symptoms include water-soaked lesions on leaves, bronzing or browning of leaves, and wilting. More severe chilling injury can result in stem and leaf collapse. Young plants, including plugs and cuttings, are more susceptible to low-temperature damage than mature ones.
Some cold-sensitive crops develop temporary symptoms, such as pale green or yellow-green leaves at moderately low temperatures. Freezing injury is more obvious, with tissue dying and turning brown or black. Rooted plants can recover from mild to moderate chilling damage, but affected tissue may need to be removed and additional production time may be needed. It is generally best to dispose of and replace young plants with chilling or freezing damage.
Can you grow plants in a unheated greenhouse?
Growing plants without heat can be achieved using cold frames or hoop tunnels in a greenhouse. However, it’s crucial to vent the heat on sunny days, even on cold days. Adding thermal mass can help moderate the temperature in an unheated greenhouse. Initially, the greenhouse had no temperature-regulating features, so the only way to control temperature was to open or close the doors and windows.
What is the lowest hardiness zone?
The Cold Hardiness Map is a tool that employs a categorization system based on the average annual minimum temperature observed in a given area. The coldest USDA Zone is 1, which experiences temperatures as low as minus 50 degrees Fahrenheit, while the warmest USDA Zone is 13, which has temperatures above 60 degrees Fahrenheit. The map’s colored zones are separated by 10 degrees, and users can locate their area by matching the corresponding color.
What is the coldest gardening zone?
Canada is divided into various climate zones, ranging from 0 (coldest) to 8a (warmest). Each plant we carry has a Hardiness Zone rating, which indicates its ability to be grown in your area. It’s crucial to choose plants that are suitable for your climate zone, as they have adapted to the specific conditions of that area, such as temperature, rainfall, and soil type. Plants not suited to your climate zone may struggle to survive or perish, wasting time and money.
Selecting plants with a Hardiness Zone rating matches your area ensures they will thrive and provide aesthetic appeal to your garden. Additionally, choosing plants well-suited to your climate zone can reduce the need for excessive watering, fertilizing, and other maintenance practices, saving time and money in the long run. Understanding your climate zone and selecting appropriate plants is essential for creating a beautiful and thriving garden.
What is the warmest plant hardiness zone?
The USDA Plant Hardiness Map divides North America into 11 hardiness zones, with Zone 1 being the coldest and Zone 11 being the warmest. This map helps gardeners determine which plants are most likely to thrive in a location based on the average annual minimum winter temperature. It is available as an interactive GIS-based map or users can type in a ZIP Code to find the hardiness zone for that area. Knowing your USDA zone is crucial for correctly interpreting references in catalogs or garden books. Gardeners in the western United States may be confused by the 11 Hardiness Zones.
📹 Find Your Plant Hardiness Zone | Backyard Smart: Know Your Zone | YouTube
Watch this Backyard Smart to learn about plant hardiness and what zone you live in. A plant’s hardiness is essential to know when …
My area was moved from 8b to 9a. I understand they use 30 years to come up with the averages, but my past couple of winters have actually been many degrees COLDER than average. I don’t think the zone change is going to impact my gardening plans. I’ll continue to make my gardening decisions based on the patterns and averages of my experience.
According to this new Zoning, we have gone from 8a to 9a but the local nursery told me we were moving to Zone 7. We’ve lived here for 30 years. In that time we’ve experienced heat and drought in the summers but mild winters. That has gradually been changing. The last 3 winters have been devastating with freezes, sleet, and snow along with cold fronts following mild moments. So we have put up green houses, cold frames, and high tunnels to protect our winter crops. We’ve lost native plants that were doing fine in the previous winters so I no longer will grow Agave and Rosemary. Landscaping that doesn’t grow through the winter doesn’t get replanted so several things are off our list. What’s going on? There’s that new zoning, but there is also our experience and our experience says that Central Texas is getting colder in the winter.
Up in the True North, our environmental department re-classified the Canadian zones not too long ago also. But they dug deeper then just temperature. They identified plant species, geography and other items to come up with a very detailed zoning system. They even converted the USDA zones in Canada to their new system. The funny thing is though, since you guys down south are so much larger then us with your population and buying power, most seeds and plants still use the USDA zoning guide in Canada! And most gardeners here also! I will have to see if the data was updated here also. Love your website Scott, very informative.
Thank you for sharing your knowledge!! So grateful! Here in Northern California just 10 miles from point Reyes I am amazed at the microclimates in the San Geronimo valley. Definitely changed in past 20 years I have been here. Appreciate the work you put in to help make map updated and easy to use. Be well
Thank you for sharing! This was great information and while my zone hasn’t changed either, I’m glad they are looking at the increasing averages and adjusting accordingly. It’s mid-end November and I’m still growing tomatoes in zone 8b. I’m definitely using this as a guide, but experience as my best teacher.
Does zones really matter anymore? The weather is so wacky now, I just use it as a loose guide. Texas is so hot. I went from 8b to 9 zone. Alot of websites are not updated. My tomatoes and peppers are just now fruiting. That link you had, they should of use more colors that stand out. Because some colors are too close and you can’t tell which yiu fall under.
Still in 5A, 5B all around me, think the pavement and concrete pushed Madison into 5B. Really cool you were part of this. I would imagine other professional gardeners throughout the country were consulted on their specific locations. 30 years is less than a fraction of an instant of our climate history. Wonder how quickly the planet is warming now, compared to other events. Terrific article! Congratulations on being selected to be a part of it. Stay Well !!!!
How amazing that you got to help create the new map. It’s so interesting to hear how it’s created and used. We do things the other way around here in the UK, the changes happen so often and with such small distance boundaries that using zones for areas doesn’t work here. Instead we have a similar system but for plants. So plants here carry hardiness ratings so you know what temperatures and weathers it will survive in and you can then decide if it would work for your garden.
Wow. I think this may be more accurate. I am in northern California which had been 9a, however my micro climate is a shorter growing season. I am a new gardener and in the spring I had talked with master gardeners from UCDavis. They were the ones who told me to choose varieties that grow 100 days or less. I found that to be true since I had already started varieties with longer grow time and found they did not do as well or failed as compared to the ones that were in alignment of what the master gardeners had explained. I am now listed as zone 8b. We will see how this works out for next year. Great explanation on the development of new map.
Very cool that you were asked to be part of the review team. My zone is the same (5B) but there is now a completely new zone 6A that 10-12 miles east of me. It would not surprise me if 10 years from now, my house becomes zone 6A. The same is likely for your house 10 years from now. The way things are going, they will need to update the maps more often.
Winters here (western Iowa) are colder, setting record low temps each year when polar vortexes sweep in — people in houses with frozen, broken pipes. Didn’t use to be that way. Got down to -40° actual degrees last year. Previously, -20° was rare. Warmer temps would be welcome. Zone here didn’t change.
I was checking the climate zone on my Evan’s (Bali) sour cherry that delivered $950.00 worth of pitted frozen cherries this year, and wondered how a “Zone 5 tree” has survived in my Zone 3 in S. Central Montana. Turns out my 20 year average is now Zone 5a in a tiny “worm” about 5 miles wide and 10 miles long on the west side of Billings. We had almost a 160 day frost free season this year. The freezer is full, we canned, and dehydrated most of the rest. There were numerous trips to the food bank, including a 42 pound Musquee d; Provence heirloom winter squash, apples, kale and chard, out of our 25’ x 35’ garden and 9 fruit trees. We picked about seventeen 5-gallon pails of apples, ten 5 gallon pails of pears, and four 5 gallon pails of plums We still have about 80 pounds of Small sugar, Long Island Cheese, butternut and Musquee d’ Provence squashes in the cool basement. I estimate HALF of that will take a trip to the food bank this winter for pies, soups and side vegetables. “Climate change” is no crisis here!
Wow! Thanks! I see I have changed from 6b to 7a and the border runs right through my county, in the northeast section, only a few miles away from me. Interesting! I’m literally a five or six minute drive from 6b and I won’t change from what I have been doing the last few years in the garden. Thanks again! I had no idea it was that precise when look at the county map.
I moved recently and a week ago was talking to some farmers in my area about our zone 4b/5a because we’re in a strange little 5-mile microclimate circle. Couple days later this map came out and the dividing line is now in my yard 😂 I’m going to assume the colder, though these last few winters have been weirdly warm.
When I put in my zip it shows my town is now 9b. However, zooming in on the map there is only a small part of our town in 9b in the SW corner. So in reality where I live and most of the town is in 9a which is not a change. Not really a big deal though. I still plant by first and last frost dates and summer heat for my vegetable garden. The trees and perennials will stay the same as we rarely get close to 25F.
As soon as I saw the Oregon seal, I was wondering if this was the project you mentioned you were working on. Very cool! I tried looking at the map for better detail but it keeps crashing, at least it tells me my zip code is zone 8a instead of 7b. Probably overloaded with excited gardeners checking it😅. Congratulations on getting to work on such a neat project and thanks for the article!
Happy to have found your website! I’ve always gardened for zone 3b- the zones change quickly heading into the mountains and what they have for me has never been correct. I live not far from Yellowstone, yet we’re in the same zone as Billings??? So it got down to – 30 F a few days ago. I’m supposed to be in zone 5a. I think I’ll stick to my old ways, the microclimates here are just too crazy!
I am in the Upstate of South Carolina. I was considered zone 7b but now it’s 8a. It’s been back and forth the past few years. Last year it got to 7 degrees which is zone 7. But that’s because we had that wicked cold snap that froze half the country last winter. But we’re playing averages. So go have a zone 8 winter average means we must have had some winters that were warmer in the past. I’ll take it. I have a food forest and I’ve planted a few plants rated at zone 8 just in case I ever moved up a zone. Mainly loquats and a pindo palm with a few fruiting bananas. It may not be a true 8a yet, but we’re moving that direction and I can dig it 🙂
3 Years ago I moved from North Alabama to Middle Tennessee which is not very far, but I am still in shock and how much colder it is. Supposedly I went from 7b to 7a, but last winter we had a flash freeze that went from 53 degrees down to 10 below zero in a snap of your fingers.. the botanical gardens in Nashville lost 17 full grown mature cryptomeria trees, which I was planning to plant in my yard. If anything I consider myself to be in z6 and will not be planting anything that can’t take -10. I will continue to observe mother nature and not be fooled by a map.
I checked your map. My zone has gone up! I’m happy. Many of the fruits I like to eat will grow on trees in zone 9A but not in zone 8B- where I was. That having been writ, I have an interesting tidbit about gardening that I learned recently. Many TREES will survive in zone 9A and 8B, but the SAPLINGS won’t survive in 8B. Trees produce fruit. Saplings don’t. They’re too young. It’s the saplings that will die- not the trees. All I have to do is keep my saplings alive until they produce fruit. Then they’ll survive in both zones!
I am hoping that the USDA will continue to work on this map. I am very very close to a borderline, and IMHO, I am still zone 6A here in New England. It is about extreme winter temps, and although our winters have been mild in recent years, just this year temps dropped to -10F. So, I am planning on -10 F not -5F as the historic low (selecting 5b hardiness whenever possible). That being said, where I grew up, the change is long overdue. It is the borders – that is where I think there is some work to do…
Good morning Scott. We too are in zone 5b, but in Maine lat 45 degrees north (longer days than you) and only about 50-60 miles from the ocean where tidal head waters, tide has an affect on both water and air temperatures. We have no fruit trees, so it’s all veg we are growing. Maine. Storms/temps vary vastly. Dip in the jet stream, temps bottom out. Up the coast, well wetter and higher temps 50 degree swings in less than 12 hours. It happened last Spring. 94 degree high, one day and woke up to 40 degree low. Based on all of this, we plant by variety of plant, acceptable soil temps, and germination length. Also, frost possibility. Our last frost recorded date, on record, not average date, was May 26th. First frost, Sept 3rd. Having said all that, climate change, IMHO, is like an umbrella, that controls all of these other factors. All this considered, we have a very short growing season but, being aware of our individual surroundings, a normal 90 day garden can turn into a 120+ day season. We are no different than anyone reading this, we want to see GREEN in the garden as soon as possible, just have to know your plants. Soil temps primarily is what we use. Oh, and Green means Go. We all just have to adapt. Great info Scott, TYFS
Good to know! Hope we got a bit warmer as we were on a line. Just did front yard landscaping and questioned company if a couple cultivars of redbuds would survive here Z5a and they said yes. We still have our microclimate though🙄. I will check it out, thank you. Edit: Ugh! No such luck, we are too low and still a 5a. The higher bluff areas are 5b. Well, hope the new trees make it.
7 to 8 % of the population is colorblind. I am one of them. Looking at the map doesn’t do me much good as I find it very difficult to distinguish between the shades of colors. Might I suggest some form of various cross hatching be included with each shade of color. It would sure help those of us in the 7 to 8 % category.
The new map has me in the same zone (7a) as before, but I’m now pretty clearly in 7a, rather than right on the boundary with 6b. That said, I don’t really use these maps much, as I don’t grow a ton of perennials and I consider using them as a proxy for frost dates (as many gardeners do) to be far less reliable than actually using frost date data for my local area.
I think they should have used “C and W” (colder and warmer) instead of the A/B division when this first began… I see people get this mixed up in descriptions. I mainly keep it straight by remembering that as A comes before B, as lower numbers come before higher numbers… (And yeah, my 7b zone changed to 8a on the new map)
They shifted me from zone 7 to 8, but we had a zone 6 winter this year. It got cold enough to kill wild onions growing in the yard, or so I hoped at the time. They seemed to come back pretty well still. It was the first time I’d ever seen or at least noticed the yard looking like it did. It’s just been weird weather here the last 2 years. This June, normally our wettest month, was dry as could be and insanely hot. We got less than 20%, maybe less than 10%, our normal rainfall that month. But then August was usually mild. We’ve already had a 24F freeze that killed all the summer annuals. But then days later we were setting new record highs in the upper 80s.
zones are really amazing. I own a rental property that is one street over from me and I can grow upright elephant ears there that will make it through the winter but here at my house everyone of them dies over the winter. I also will notice that like when the first frost kills the banana tree leaves at my house the leaves on the ones at that rental house are ok for about one to two weeks later. Really weird.
I have been planting Dahlias and Cannnas in the ground and they have been making it through the winter even though I am now on the border of 6a/b in Indianapolis. It did get down to -10deg.F last winter. I suspect the frost didn’t go deep enough to kill the rhizomes. I am going to mulch more this year anyway.
I wish there was a way to account for micro-climates on the map. Technically I’m in 8a – 8b, but due to our elevation and a few other factors, I have to garden almost like I’m in zone 6. When we first moved here and saw the map said we were still in zone 8, that’s how I planted the first year…..that did NOT work out at all lol.
In the ten years I’ve lived in Zone 7b… there has not been one winter that didn’t get down to zero or below. -15 one winter and it killed half the prickly pears. Try planting a cold hardy olive, it won’t last the first winter. 5 to 10 degrees as the coldest, is the best case… I haven’t seen it but I hope to someday.
Weirdly, it shows my area as warmer and moved us up but the last 5 years have had record lows for our towns. A record set in the 40s. I had a rose bush that was 15 years old (now 20) and an even older raspberry bush. Both died from -20 degree weather. I don’t like the idea of removing outliers. That’s not sound statistics.
I live in the zip code you highlighted here! And we went to 6a which I find kind of funny after last winter. I’m pretty sure we got to -18 or -16 just last winter right around Christmas (conflicting thermometers). We also used to live in another part of town that is also now a 6a and I know it was -16 there. Moving forward it won’t have a whole lot of impact on me anyway. I’d rather have plants more suited to go through the winter with less maintenance. I do bring some of the less hardy ones in pots into the garage during the coldest months when I can, but I’d rather not worry.
While I appreciate updates and attempts to be more accurate regarding local areas. . . ***for my area***. . . I consider this a fail. We moved from an 8a to an 8b. We’ve lived in the area since 2016 and not a SINGLE year over the past 7 years has either 8a or 8b properly reflected our area. We have hit 5 F multiple times EACH year and some years lower. 8a is only supposed to hit 10 F, now we are in an area that is only supposed to hit 15 F. . . I am curious of their methodology and calculations. I know the weather station they pull the data from for my area. . . it used to be in a small parking lot and surrounded by fields. Not anymore. Now there is an elementary and a LOT of pavement and asphalt. This isn’t going to affect how I do anything, but I feel bad for people that move into the area thinking 8b. . . . and spend MONEY on those plants, because they WILL die.
Near as I can tell, I went from the northside of the 9a/9b line to the southside of the 9a/9b line. So… still zone 9, but things might be a little less likely to get hit by frost. Bismark Palms would still get killed in a bad freeze and still not warm enough to grow mangos. But growing apples and blueberries got a little tougher!
Howany of these weather stations they get data from are in heat islands, next to parking lots or next to buildings that have been built in the last 30 years. I have been hearing stories for the last 3 years that plants have been getting burned more thna in previous years. No matter what they publish natiral cycles and variations in local climate will top their science. We have had increased winds from the south rather than the north in winter time. Everything changes with the greater cycle of the universe. Good luck. Plant more varieties and save your seeds. You will need them.
Question? I’m in wester NY, 6a and it did not change. This year we just had are first killing frost, but it snowed a few weeks back. The next street up is 6b. I’m confused because I watch the weather for the past 6 years and even mark lows and highs and I totally disagree with there extreme lows. I haven’t recorded a below 15 reading. So how are they coming to these results? Love the new map❤
My biggest concern is how fast and big everything is growing! Waaay different this year especially, than even last year,. Also, the deer are eating things they had NEVER touched before. This causes me to think the growth speed is causing fewer nutrients in everything they’ve been eating since there were deer, thus they are expanding their diet. I blame the rise is CO2…
the hardiness zone map for Canada was interesting. Sent to me by a climate alarmist showing zones moving north, a closer look showed where I lived in Saskatchewan the zones moved south. we were zone 2 almost zone 3, and the new map had us zone 2 almost zone 1. Trust what you see, not what you are told. It looked like areas that had an increase in population and had airports surrounded by urban sprall had an increase in temperature, while the areas that had little change in population and urban sprall actually cool. I farmed 600 acres and know for a fact it cooled. so we moved to Missouri.
Scott, how do you balance the 30 year average vs the coldest recorded temp for an area? For example, Denver / Aurora moved from 5B to 6A (-5 – -10F) based on 30 year average, but last year, Denver had its 2nd coldest (1 time) temp (-23F) in recoded history (approx 150 yrs of record keeping). Thank you.
This map just does not apply to my address. I am above the 48th parrallel and it has me as 6b. I have been here 7 years and every one of those years it has gone below -5, last year -15. My local extension service advises us to be guided by the pre 2012 map… buy plants for zone 5 or less. I lived for 60 years in zone 6, and the mountainous inland northern border of the USA is not zone 6, no matter what the data crunchers say.
My area is still 8b, but the temps in winter have been colder. When the weather predicts a temperature, it is at least 5 degrees colder. I put up a green house to protect plants I did not want frozen. I am suspect of the government changing this with the climate change agenda. If someone plants food and it all freezes, you starve once the food gets cut off. We had a hard freeze in October, I measured 24 degrees at my farm, when we usually don’t get a freeze until Mid November, and usually 30 degrees. Cooling, not warming…
The climate zones in the US have been moving north at a rate of about 13 miles every 10 years. I’m still in zone 7b on the east coast. We’ve been getting noticeably warmer winters since moving here. However, recent years have had cold springs that delay the start of the growing season, then Indian summers that last well past the end of October. While I still cannot grow cold sensitive plants outside through the winter, this does open up new possibilities for what might survive in the greenhouses.
You can’t take the map as a guarantee to buy and plant specimens “appropriate ” for the zone it says you’re in. It only takes 1 cold night to kill off anything not hardy enough. The map is based on averages, which your precious plants don’t care about. Nurseries and large retailers can’t be trusted either; they’re selling things because people are buying them, not because someone who has lived in the area their whole life endorsed the product line. If you want to buy a plant and are unsure if it’s tough enough, Ask an old-timer if they think it will make it.
I live in the southwest and, anymore, I would find a map of heat zones considerably more informative than this. It’s not the cold temps, which have increased just slightly that affect my garden and yard. It is the heat, which has had a more dramatic change. I am now worried about getting my garden in to avoid the earlier and longer heat, much more than I am worried about a possible late, and rare cold snap. I need to be able to identify which plants can tolerate high temps more than those who can survive the cold, and when to anticipate heat -not cold.
Hi @Gardener Scott, The USDA could not have selected a more qualified technical review team member and beta tester than yourself! Perhaps your presence would explain the paradox of just how this updated map (a neuro-typical resource) could be so profoundly clear, comprehensive, and unambiguous (my theory is that you’re either on the autism spectrum or have 180+ IQ. Most likely just the latter. Possibly both). The new map appears to be the antitheses of ‘neuro-typicality’. Fascinating! 🙂
I’m a GIS analyst by training, i work with lots of national data sets (for canada but its a similar scale) and as close as you are to the line I would say don’t really assume your yard fits nicely in either zone. On a grid that course on a national sclae that line could have a buffer that extended for miles in either direction and it still would be fuzzy if your specific yard really fit into one or the other zone. As somone who works with this stuff more than most people I understand the need to draw those lines somewhere but I also understand equally as well how much more concrete they seem compared to the reality on the ground. I was working with similar climatic data once and disticltly remember a conversation where I had to explain to someone that it’s not like the clouds part and a beam of light shines down on one side of the line all year but not the other haha. Also great advice on dropping down a one just to be safe.
The old map was not accurate for our area and neither is this one. We should have been moved back not up. We are now listed if we zoom in as 7a…there is no way. I can see that to our west a couple miles because they are 2000 feet lower. 1/2 mile to our east it is listed as 6b. This also I feel is too high. I rarely can get zone 6 plants to survive with out extreme protection. Our temps are always colder than what they say for our zone.
The methods they use to make those maps do not really work. Plants do not care about 10 or 30-year averages. One bad winter and those plants are fried. It’d be more accurate if it’s with absolute absolutes. For example, for the last 10 years, it’s : 1: -10F 2: -10F 3: -10F 4: -10F 5: -10F 6: -10F 7: -10F 8: -10F 9: -29F 10: -10F you should be a zone that is for -29F (zone 4a ) not the average – zone 5
The new map is very inaccurate for the I-35 coordinator. Mostly because it doesn’t take into consideration data from 2021-2023 where coldest days were 10+ degrees colder (2 hardiness zones) than the old map much less the new map. I understand its the average over x years but on areas that lie between the airid and humid climates the variance of winter lows vary drastically as it can greatly change based on golf moisture (warmer) or lack of it (colder) you get in a winter. Meaning the new data misses a near record lows we got that would have left or shifted the map to be in a colder zone.
It’s so sad that the USDA is STILL using the primitive 10+ zone map. In the West, we have had a more complex, and more reliable 24 zone map for more than 50 years. It reflects not only minimum but also maximum temperature, altitude, dry winds and air drained situations, ocean and lake influences, etc.
These zones are completely worthless in Northern California. Too many microclimates here. What does it matter when your average last frost date is if you typically get 2 straight weeks of cloudy cold days a month after this date? Your plants suffer in bad weather. It doesn’t have to freeze in order to stunt/kill your plants. Maybe these zones work for others. They are completely worthless to me.