|We've been arguing at work over what zone we are in. What zone is Pittsburgh, Pennsylvania? I say it is zone 5, but other people at work say, well|
|The winter hardiness zones work based on average minimum winter temperatures, and within each zone there are designations of A, meaning the colder part, and B, meaning the warmer part of the zone. There are also undocumented microclimates so if you lived in what is ostensibly zone 5B but have a sheltered location with wind protection and with lots of heat holding concrete around you for example, you might actually be gardening in a zone 6A microclimate. And your gardening friend a few miles outside of town in a windy, exposed, rural spot might be in a microclimate better considered zone 5A. So the zones work as a rough guideline but individual circumstances may vary often by as much as a half a zone.
Using your zip code, you are in a nominal 6A -- so it's either a solid 6, a cold 6A, or a warm 5B. I guess that doesn't give you a firm answer but I hope it helps explain why there can be so much discussion about it. Your plants will tell you better than the map ever can. If you consistently lose plants considered hardy to zone 6, then in your garden you are probably more of a 5.
Never say never but ... you can sometimes hope for a half zone gain based on microclimate, but to gain from the colder part of 6 to a solid 7 is unlikely. You can experiment and see, if you have sheltered spot up against a building that would help hold some heat and you also mulch well in late fall and if the plant is well established and very healthy going into the winter, it might work -- at least during years when there is good snow cover to help insulate the plants during the coldest months or in years when you experience a milder than usual winter. Also in my experience plants that require good drainage are often lost in winter if the soil is not perfectly drained even if they should be hardy in your zone, so take that into consideration as well.
You can try to overwinter plants in a garage or unheated cool basement. It is important to allow them to go dormant outdoors in the fall, then bring them in for the coldest months (keep them dark and cool/cold but above freezing, the soil should be just barely damp not bone dry -- this helps keep them dormant), then take them back outside in the spring so they can wake up normally with the season. Sometimes it takes some experimenting to figure out what works best for you.
If you want to check more zip codes, here is a chart you can use. There is also a zone map and some explanation about how to interpret the information.