Zones - are they meaningless?

[caliloo]

I iread with interest that the USDA has recently rezoned many areas in the US, including mine. For a very long time, Bucks County (just north of Philadelphia) was considered zone 6, it has recently been recategorized as zone 7.

I believe (correct me if I am mistaken) that the zones are determined by *average* winter low temperature. Now if the actualy temperatures were close to the average on a daily basis, then I could still put faith in the zone maps. However, that is not the case in most years and certainly not the case this year.

In January, we had several days in the mid-60's, even reaching 70 on a day or two. Of course, this caused all sorts of plants to break dormancy, most notable several roses began to leaf out in ernest. Move ahead a couple of weeks and we are now enjoying single digit temps every night and highs in the teens during the day.

If you *average* these temps, along with the other more normal temps we've expereinced, then maybe it would factor out to what the USDA considers a zone 7 garden. The truth is, I have grave doubts that many of my hardy to zone 7 perennials are going to make it after a week of temps like what we are experiencing.

So what do you think - should zones reflect *average* temps or should there be a better method for determining a plants survivability in your area......

Inquiring minds

Alexa

[maidofshade]

I was also just dreaming of what could grow here now that I have be also upgraded to a fringy zone 5 but with temps down to just about 20 below this week I will stick to what I know will do well here. My husband said that it isn't so much the highs and lows but you must figure in the wind and also the freeze and thaw that usually does the plants in. We have been having luck with apricots--usually the blooms get caught in a late cold snap, so we bank them up with snow and have some on the north side of buildings so they don't break their dormant cycle too early. My feelings are that there are more things to consider as the big picture as far as what will grow in your own backyard. I would not mind losing a few perennial plants but trees or other more major plantings are what makes me stick to things I see doing well for several years in someone else yard. I do dream of Japanese maples though but I am not willing to drag a large pot of them somewhere to hide for the winter.
I wish it would be simple but I am not sure anyone can promise we won't still have a year here or there with very cold weather or very late spring frosts.
Does anyone know how they come up with the zones????????
Sorry to ramble but this is very confusing. Also alot of nurseries carry Plants that are not zone hardy here and that also makes me crazy. (crazier )
Cheryl

[kHT]

What is average these days? Zonal Denial here!!

[viktoria]

I thought it had to do with minimum temperatures as well: how cold it actually gets in winter. For example, one's average temperatures might say he/she is in zone 6, but a plant that will not tolerate temperatures below -20 won't make it there if there are a few nights at that temperature, no matter what the average temperature for the season is.

[John]

Viktoria is correct, so I think zones are still of some use. Here in zone 6/7, the temperatures would rarely drop below zero, so that is of some help selecting plants, even when one decides to challenge the 'rule'.

I have a small collection of hardy bamboos, and it makes it much easier to keep the zone in mind when acquiring those more likely to survive here.

[DryGulch]

Fellow gardeners, determining your zone is a bit more complicated than the maps would have you believe. It is actually a complicated formula using number of days at certain temperatures,coldest temperature, number of days below a certain temperature, last frost date, number of days below freezing in a row, etc., lots of stuff. It is a pretty long algorithym.

Once when I lived in the greater Chicagoland area, it didn't freeze that year until after Dec. 1. I had dahlias as table centerpieces in Dec. from my own garden. That got me interested and I researched it and plotted out the zone for that particular winter. It ended up as a 7B. At the time we were classified as 5A. I see that my old home is now squarely in zone 6, which follows what I had intuited, as I was able to grow certain zone 6 plants there over 5 years ago.

The USDA map is based on more than one year of historical data using the complicated algorithym.

[John]

Interesting.

I still think of zones as a useful guide, but as something that can sometimes be successfully challenged.

When I am talking to a garden friend in zone 9 FL, I know that she cannot grow apples, or peonies... or dormant daylilies (for long.) It helps.