Hardiness Zones and Islamabad

Now now, this could be a whole can of worms. Whenever I go to find any information about any plant there's always the Hardiness Zone described next to it. My location Islamabad falls somewhere around 9a and/or 9b. That is all well and good because it tells you how much cold the plant will tolerate.

Now where it gets muddy is how much HEAT the plant will tolerate. Because you know it so often happens that you buy a plant in spring, it does look beautiful and seems to be thriving but come summer and you have to do a thousand things just to keep it barely alive (forget about blooms and stuff). 

A good example can be Oxalis. Its a beautiful plant, perfectly suited to my climate according to the Hardiness Zone described (Zone 8a-11). It is also described as a semi-shade plant so out you go, buy a pretty looking plant and plant in a semi-shaded spot. Then summer comes around!!!! The temperature is hovering around 35 degrees Celsius for most days from May until early September and you've got a problem!! The semi-shade bit goes right out the window and you have to find a fully shaded spot but that may not guarantee you any luck with this plant either. It may still require watering 3-4 times a days (yes I know!!!!). Even after doing all this and keeping the plant barely alive there's another surprise HUMIDITY!!! The monsoon season in Islamabad (July-August) will see most days as having 70 to 80% humidity and sometimes even in high 90s. Combine the heat and humidity together (Its like living in Arizona AND Florida at the same time) and all that extra watering and shady spot doesn't seem a good idea anymore!!! 

CONFUSED????? .................... Welcome to the club!!!!

One solution to this problem is to know your Heat Zone. Heat Zone system has been devised based on the number of days an area has when the temperature reaches at least 86^oF (30^oC). Now the AHS (American Horticultural Society) Heat Zone map goes upto Zone 12 i.e. having days of 30^oC or above for more than 210 days per year. By my estimation (correct me if I'm wrong) in Islamabad there are at least 250 days a year with such high temperatures  so we're way off the map (Zone 14 approx if there was one). This may help you find the right plant but the Heat Zone system is not widely used yet and most web-sites or books will not give you this information.........So we're still in the trial and error stage.

In my opinion the only feasible way out of this dilemma at the present moment (until there is a Pakistan/Sub-Continent specific zone map) is to introduce new plants by trial and error. But as you fellow gardeners and plant lovers will know what a heart-breaking experience it is to buy a plant, see it grow before your eyes and the see it  just drop dead a while later. 

So the search for an accurate zoning system continues........