I have heard some disagreement about 'zones' from bamboo enthusiasts and gardeners. Can I ask if everyone on here is going by the USDA Plant Hardiness Map or if they use something else? I think it is important because when comparing growing habits in various zones it would be necessary to all go by the same metric. I for example have only had bamboo gardens in a zone 8b per the USDA plant hardiness map, but all of the local nursery 'experts' insist it is a zone 7. Curious if anyone has some insight here on what the right resource to use is to determine ag zones. Thanks!

USDA Zones are maybe good for very rough comparisons but on an individual basis conditions are just too varied to throw them into such few categories.

What exactly does it mean to be in zone 8b? Wikipedia states that 8b is a minimum temp range from -9.4°C to -6.7°C. Notice there is nothing on the maximum temperature, how long these minimums can occur and when in the year they might occur. Precipitation, light intensity etc. is not factored. In short, a large portion of the factors that make up your climate zone are actually not considered.

Let's face it, if we want to compare conditions to our local environment we need as much data as possible. At least it gives us a good reason to troll the internet with our thoughts and estimates on bamboo and other plant hardiness

This has been a matter of much confusion for me as well. Here is what I know. There are three main issues complicating this issue.

The first issue is that we seem to be trending toward a warmer climate in the U.S. and the climate maps have been recently updated to reflect this. Sometimes resulting in a supposed increase of 2 (half zones-ex 6b - 7b) for some areas.
The second issue is that there are multiple zone maps going around. The main two being the USDA map and the Arbor Day map.
The third issue is microclimates. Cities are a prime example of this and sometimes can be a full zone higher than the surrounding area.

In the end your best bet seems to be to look around you. If it will grow in your neighbor's yard in similar conditions (aka sheltered, full sun, etc.) it will probably grow in yours.

To demonstrate the hardiness map issue i will show you some links.
Changes:
https://www.arborday.org/media/map_change.cfm
http://www.washingtonpost.com/wp-srv/special/local/planthardinesszones/index.html?tid=a_inl

Current maps:
https://www.arborday.org/media/zones.cfm
http://www.planthardiness.ars.usda.gov

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As stated above, the hardiness zones are a general guideline. Day length, micro climate, inland, maritime, altitude, all come into play as far as plant performance is concerned..

Also, the USDA zones are based on averages, it is not uncommon to have weather events that fall outside of zone temp parameters.

For instance, in the last couple of winters have seen zone 6 and lower temp events here, where it is supposed to be zone 7a. My plants were set back accordingly. Even though temperature averages for the year were closer to 7b.

For plants I provide my customers, I'll tend to be pessimistic about what zone we are in; better to provide a zone 6 plant that lives than a more marginal one that gets set back while under warranty.

Good feedback, but Nicholas, the metric of Ag Zones I think is very important. I know you mentioned a variety of other facts to consider such as precipitation and amount of sunlight etc. but the Ag Zone is especially important because it is a factor that cannot be manipulated as easily. I can control sun hours by opening my canopy or planting my bamboos in full sun or part shade or full shade. Also I control the 'rainfall' by watering as much or as little as possible. However the average lowest temperature over a span of a decade or so seem more critical in determining which plants will die or not. Even hotter than normal temperatures will not kill any bamboos that I own. But putting them in the ground in an area with extreme lows for a given variety will result in top kill or the death of the planting altogether. So I do find that Ag Zones are very critical, maybe more than anything else. Essentially I want to know what my plants will experience on the low end for temps. Of course it is not 100% since it is simply an average of past lows, but a good barometer nonetheless. Although I agree nothing beats simply seeing what grows down the street from you All good except that us bamboo nuts generally are not in huge numbers in a given neighborhood!

the Zone 7 the nurseries are talking about is the Sunset zone 7 which is the upper foothill zone out here . Zone 9 is the lower hills and 8 and 14 the valley. its a more specific zoning guideline than the usda zoning which is very general

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Jason Floyd
Hangtown Farms

Emmett Idaho
Zone 7A
Potato country

In my area heat is usually also not that much of a problem but there will be people with hot and dry areas that struggle to keep boo like fargesias alive. If you want a common ground for discussion obviously you also have to include climates dissimilar to yours!

Average lows are definitely not the best metric for determining plant survival. All it can take is a few hours of extreme cold to topkill or completely erase a plant.
When you have an average value it is not clear how extreme outliers can be. It makes a huge difference if most of the year you have moderate lows and then once in a while it gets extremely cold or if it is a bit colder more often but you never see those extremes. The average lows of both will look similar and don't tell that story.

For instance where I am from we generally have mild winters with almost no frost till well after Christmas, after which you can get cold spells of -20°C and lower for short periods of time.
This does not happen every year so it adds to the problem. Slow growing plants that are marginal at that temperature may or may not make it depending on the local micro-climate.

I'd argue that you can't separate out single factors as they are all interconnected. Soil composition can make a difference in combination with temperature (even day and night differences), wind exposure and precipitation. It explains why people have quite varied reports on hardiness and also why seemingly one year a boo will do fine with a specific minimum temperature while another time much less lows cause leaf loss or even topkill. This year my aurea and violascens (potted) had massive damage with a low of not even -15°C for just a couple of nights while fargesia/borinda gaolinensis which was standing right next to them had almost no leaf damage. I have no idea why as the gaolinensis is usually much more sensitive.

A truer climate zone map would more closely resemble the typical topo map in many areas, given the fact that 1000' elevation is usually a 3F degree change. There's a 5F degree change on my daily jogging route. I probably posted earlier that I used a local online reporting weather station's historical data to confirm the Arbor Day map is more accurate for us.