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Old 01-04-2018, 04:51 PM
 
Location: 46060, Hardiness zone 5b/6a
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Ok, ok, I know that this question might be considered a bit repetitive in its nature, but, I realized that the USDA finally updated the National plant hardiness zone map back in 2012, the first revision in over 20 years, but after the past several winters, I am beginning to question the validity of these maps because even though the latest map shows the Indianapolis area as being designated as a zone 6a, this winter thus far has been a zone 5b winter in the city of Indianapolis, and winter isn’t even half over yet, the lowest temperature registered so far this winter in the city limits of Indianapolis has been between -12 F and -14 F, Which is obviously not a zone 6 winter, the winter of 2013-2014 also saw low temperatures dip below the zone 6 designation, The lowest temperatures I recall seeing that winter were in the -14 F to -16 F range.


So I guess my most legitimate questions are as follows:


1. Is the USDA hardiness zone map really all that reliable or factually accurate? 2. Also, in your particular hardiness growing zone, how far from the “Average” annual extreme low temperature have you seen your location get to in terms of standard deviation?


All thoughts and opinions on this subject are all held in high regard and greatly appreciated
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Old 01-04-2018, 05:11 PM
 
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I know the coconut line has moved a good 30 miles more to the north since 1981 in FL. It has warmed up so much since 1990 they are growing in Tarpon springs. All plants and zones will need to be adjusted more often as the planet warms at a more rapid rate.
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Old 01-04-2018, 05:25 PM
 
Location: The Driftless Area, WI
1,618 posts, read 616,368 times
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Quote:
Originally Posted by Isleofpalms85 View Post


1. Is the USDA hardiness zone map really all that reliable or factually accurate? 2. Also, in your particular hardiness growing zone, how far from the “Average” annual extreme low temperature have you seen your location get to in terms of standard deviation?


All thoughts and opinions on this subject are all held in high regard and greatly appreciated
Astute observation and excellent question, and I'm glad to see you use the term "standard deviation," suggesting you see what should be a role for statistics in determining the answer.

The fact that there is an obvious ignorance of reality by those who made the changes shows how "The Deep State" and politics permeates all levels of our federal govt. "Global Warming" continues to be the mantra of those with an agenda, despite the fact that we went almost 20 yrs with no discernible warming in the records, and that it took deliberate fudging of the data to show a slight warming the last year or so.

If you take the yearly average temps of the Central Anglican Record, the longest record available for a single area, going back 350 yrs, you'll see no single year was more than 2 St. Dev away from the mean for the entire period-- ie: there's no "GW." There are cyclic changes in weather. There are several different cyclic influences: solar cycle, cyclic changes in Atlantic & Pacific Ocean temps and changes in the Milankovic Cycle, among others.

The Hardiness Zones are delineated by lowest winter temps and divided into groups based on changes of 5-10 degrees. When the changes in temps measured over the past several decades show a rise of only a few tenths of a degree, why should these zones be re-defined? Is their revision based on science (obviously not) or something else (like politics)?
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Old 01-05-2018, 01:23 AM
 
Location: Northeast Tennessee
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With the weather this past week, it would make one wonder. lol. TWC was saying this evening that both Savannah GA and Charleston SC have had the all-time "low" high temperatures the last 4 days. Also, the next several nights are forecasted to be well below freezing, even down into northern Florida. You have to be careful and if you plant something even a little of the hardiness range, be sure to protect.

I live in northeast Tennessee (zone 7a - on the edge of 6b) and I have several Needle Palm trees. They have done fine the last couple of years with no protection, but a few years ago I lost a couple when it got down to about -11° in January-February of that year (which was about 36° below our average low for that time period - as our coldest average low is 25°) and they were supposed to be hardy down to about -20°.

This season, the last few days we have been experiencing (like everyone in the east) some of the coldest temperatures we have had in a few years and I actually have some of those outdoor flood lights shining on a couple of my palms to be safe. They put off a little heat (using the halogen bulbs), so that should help them.

I am interested to see how many of the southeastern palms hold up these next few days. I know that Spanish Moss does not like super cold and dry weather and parts of the southeast coast there it is everywhere is forecasted to have lows in the upper 10s and lower 20s for the next several nights and only in the 30s for highs. I hope it isn't destroyed.

We actually have some Spanish Moss that my cousin brought me from her house in Columbia South Carolina. We had it in our cypress tree since the spring and brought it in the sunroom the other night and keeping it moist until we can take it back out.
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Old 01-05-2018, 07:07 AM
 
Location: East of Seattle since 1992, originally from SF Bay Area
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There will always be exceptions, more lately. Those plants that are listed as hardy in your area may, at time require additional protection to survive. When we lived in California I lost a very nice, older bougainvillea one winter when the temperature dropped to 20F. It was too big to protect by covering with anything insulated enough to keep it from freezing hard. We are now in zone 8B, minimum 15-20F, but have been down to 10 a couple of times.
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Old 01-05-2018, 09:06 AM
 
1,004 posts, read 517,944 times
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I think the USDA zone map shows the *average* minimum low temps. So in any given year the minimum low temp is likely to fall within the zone's range.

But the zone map doesn't include the extremes, the all-time minimum lows for an area. That gives you more of an idea how low it potentially can go.

In the places I have lived, generally the extreme lows were actually 1-2 zones colder.
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Old 01-05-2018, 01:54 PM
 
Location: Minnesota
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I've had luck with a few plants that are doing good out of their zone. I'm In 4b, Minneapolis, and started some French lavender, (said on package hardly to zone 7,i think) by directly sowing into a small garden area. I tried starting indoors but they always die on me, seedlings are finer than hair. I thought I would do just to see if it was possible. It is in a spot that my house block wind from two directions. The first year it grew but no flowers, second year flowers, and has been doing well for eight years, in same spot. The plant get a little larger each year but not by much, I don't really know how rigorous it is in preferred zone. Two years ago I dug a small one up that had self seeded and gave to sister. She planted it in a semi protected spot and it still alive.

Anyway, long story short, you can get away with planting things outside its zone it you can create a micro climate or protect in some way.
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Old 01-05-2018, 02:45 PM
 
1,480 posts, read 789,195 times
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Quote:
Originally Posted by noodlecat View Post
I think the USDA zone map shows the *average* minimum low temps. So in any given year the minimum low temp is likely to fall within the zone's range.

But the zone map doesn't include the extremes, the all-time minimum lows for an area. That gives you more of an idea how low it potentially can go.

In the places I have lived, generally the extreme lows were actually 1-2 zones colder.

think you're right. the USDA zones are at best a ROUGH guideline for the "average" lowest winter temps and do not factor in the "un"average extremes of cold that may come every once in awhile and hurt or kill otherwise "hardy" or "adapted" plants. IMHO, plants themselves are the real best guide to what can be regarded as reliable in a given area. take a walk or a drive through the older parts of your town and see what has probably gone through all sorts of weather over a long period of time---that is likely the "bone hardy" stuff that may be the basic plants for your garden. look at parks and botanic garden for "new" and different plants that you don't see in the older sections---some of these MAY be reliable additions to your garden.


after you looked at what's actually growing then you may want to compare it with "recommended" and "indicator" plants for the USDA (or Sunset Western Garden Book or Southern Living Garden Book for that matter if you're in the west or south) and see what matches up. no matter what the USDA or any other "expert" says should (or should not) grow where you are IF you seeing a plant growing, growing well, and growing long term then it's probably "hardy".

plants are living things growing and changing in an environment that itself is changing through "natural" variances in heat, cold, moisture, and drought in natural ways further complicated by how we may treat the plants by "artificial" means of add water, fertilizer, winter cold or summer heat protection, etc. and by our loving attention and/or casual indifference. it's hard to fully predict or know just what they will do and how they will grow under the particular climate and micro-climate conditions of our particular garden and often the truest thing we can say even to our next door neighbor is, "it'd doing o.k. now and has done so for a number of years for me---it MIGHT just do the same for you!!!".
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Old 01-05-2018, 04:32 PM
 
Location: Forests of Maine
29,682 posts, read 47,391,075 times
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Ask a local or Master Gardener in your area. I have been here since 2005, I see what the low temps are, and whenever it matches my USDA 'zone' I make note of it.

In my area I know others who grow things I can not grow. There are micro-climates and variations that must be considered.
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Old 01-06-2018, 09:28 AM
 
9,168 posts, read 7,234,472 times
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How are you using the hardiness zones? I use them as a general guideline. I use trial and error to get empirical data.
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