Plants for a warmer world

    Recently the USDA made it official: the Philadelphia area is now in plant hardiness zone 7.

    That may not mean much to everyone, but gardeners will know that it means we are now out there working in a warmer climate.

    It’s based on a map the USDA puts out, which separates the country into different zones based on the average annual minimum winter temperature, divided into 10 degree increments. We used to be zone 6. 

    On a number of levels this news is troubling, even terrifying, and incontrovertible evidence that our climate is changing. But I’m going to serve some good news with the bad. If you’re a gardener, now there are a lot more plants you can grow. 

    When I came to this area almost twenty years ago, you couldn’t reliably grow trees like crape myrtle or southern magnolia. Camellias were touch and go, as were lavender and rosemary. Figs? You could maybe a crop every couple of years when the plant didn’t die back during winter.

    But things have changed. All these plants are now completely reliable in Philadelphia, and our selection of what’s growable has expanded considerably. In the past year I’ve been surprised to visit Philadelphia area gardens overwintering hardy cactus, calla lilies, several kinds of palm trees, and even giant bananas. The bananas died to the ground in winter, but sprang up again in spring and were twelve feet tall by September. 

    Since I heard about the zone change, in my own garden I’ve decided to try out a gardenia bush and a couple of pomegranates, as well as a few eucalyptus plants, which aren’t looking happy since it got cold again. Inn theory at least, all these plants are hardy to zone 7.

    I’m not saying climate change isn’t scary; it’s likely to bring tremendous unpleasant consequences. But a longer growing season and milder winters have also created opportunities for adding new kinds of plants to gardens, both vegetable and ornamental. It’s a new environment, and we’ll have to adapt to living in it and possibly switch to trees and plants that can adapt to it as well.

    Not all of them will. Some plants that have been garden stalwarts in Philadelphia are already harder to grow. The old fashioned Lilacs are really not fond of long, hot summers, and they may become more of a memory than a presence in the coming years. 

    Which is all the more reason to start looking for some replacements. Because when life hands you lemons, you might as well make lemonade. Or these days, pomegranate juice.

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