Zone 7: What does it mean for Long Island gardeners?
October 05, 2010 | 07:07 AM
Repeatedly, Long Island gardeners are told that we live in Zone 7. This is a fairly mild zone, as far as plant winter hardiness goes. It dips down as far south as Texas and New Mexico.
Other experts warn that well, yes, we're in zone 7, but occasionally we have a very cold winter, one cold enough to kill some "tender" plants.
Still other experts warn of "microclimates" that is, small areas on Long Island that have a slightly different climate from the rest of the area — either milder or colder. And yes, microclimates can be found in an area as small as part of your back yard. So you could actually have an area that is zone 6 where you are gardening.
Finally, the Arbor Day Foundation remapped the U.S. in 2006, noting that in general temperatures have been warmer. Long Island is still in zone 7, but more firmly now.
Although the idea of mapping the climate zones goes back to the 1920s and 1930s, the U.S. Department of Agriculture produced a map in 1960 based on how cold it gets each winter. This way people would know what plants would survive their winter. The map was then updated several times including in 1990. Long Island is in zone 7, a zone which generally has no colder temperatures in winter than between 0 and 10 F. The higher the zone number, the warmer the winter is expected to be.
Note, however, that successful gardening also depends on humidity or lack thereof, rainfall and summer heat. So we can't just go by the hardiness zones in selecting plants.
Gardening in zone 7
In general, I prefer to select plants which are rated for zones 6 and above. Six is a zone slightly colder in winter than we usually have. I do this because if, as the experts say, we could have an unusually cold winter, my plants should survive.
But, looking around Long Island now, it's obvious that plants which were rarely seen here are now found in abundance. For example, golden deodar cedar is rated as growing in zones 7 and above. Yes, there are more and more of them being planted here and obviously thriving, since they're getting so big. They've gone through many cold winters.
Another "warm" weather plant is the hibiscus, so associated with places like Hawaii. Those dinner plate size flowers can be seen almost anywhere now with many varieties cold hardy into zone 6 or 5 — check the tag that comes with the plant. Mine even survived last winter's bitter cold in a pot when I waited too long to plant it in fall.
Crepe myrtle is definitely considered to be a southern plant, yet their gorgeous blooms were very visible this year and not just on small, new plants. Many are enormous, having been growing here for 10 or more years like the cedar.
One plant which I haven't seen survive well here, which is rated for zone 7 and above is the Easter lily.
What does all of this mean for you, the gardener?
• Check out your new acquisitions carefully. Plants rated for zone 8 and above will not survive our winters.
• Consider growing your more tender plants in moveable tubs. My three fig trees did very well this year, having overwintered in an unheated garage.
• Don't invest a tremendous amount of money in plants rated for zone 7 or above since it is entirely possible they may not make it over winter. Losing a $20 plant is one thing. Losing a $200, $300 or more plant is quite another. If you insist on a tree that is rated for zone 7 and above, go to a nursery that guarantees their trees for several years. My golden deodar cedar was guaranteed for five years as long as the nursery planted it.
• Prepare for dieback. Crepe myrtle can do just that. So can some hydrangeas. However, since crepe myrtle blooms on new wood, you'll still get flowers, it will just be later in the season and the plant may remain a bush rather than grow to tree size.
• If you have an iffy plant, locate it in a more sheltered area, such as the south side of your house or behind a sturdy, solid fence which blocks cold winds. Make sure that you generously mulch any you are concerned about.
• Research each individual plant carefully. Some varieties of a species are hardier than others, having been specifically developed for colder weather. Others will survive if you wrap them up — such as fig trees.
• Remember that just because a plant is sold on Long Island, it doesn't necessarily mean it can survive our winters. I've seen Christmas evergreens which are not hardy and hydrangeas listed for zone 8 to 11 sold here. Look for the specific zone on the plant's label or terms such as "hardy" or "cold hardy" before investing in them.
Ellen Barcel is a freelance writer and master gardener. To reach Cornell Cooperative Extension and its Master Gardener Program, call 727-7850.