I find this pretty amazing, especially when you think about this process going on in each and every leaf in the garden.
What Will Grow In My Hot Garden?
Plants have adapted to their native habitats over hundreds, if not thousands of years. They can usually come to terms with the vagaries of their local weather and survive the periodic stress of hot and dry periods. This is one of the reasons that ecologists are recommending the use of native plants in our gardens. This is a laudable goal, if not carried to extremes, and one of the ways we can limit plant stress in our gardens when the weather is not cooperative.
But, as gardeners, we grow plants in our gardens from far corners of the world for many reasons, including the fact that "foreign" plants enrich our gardening lives. In the US, the climate varies so greatly from one part to another that zone maps have been developed to help us figure out what plants might survive in our gardens. (Maps illustrated link to larger versions.)
Hardiness Zones
A number of hardiness zones have been devised and published, but the one most usually referenced is the USDA Plant Hardiness Zone Map. In 1960, the USDA (United States Department of Agriculture) published a plant hardiness zone map. Its creation was sponsored by the American Horticultural Society (AHS) in conjunction with the U.S. National Arboretum. An update was published in 1990 with data collected from 8,000 weather stations between 1984 and 1990.
The map divides the country into eleven zones based on average annual minimum temperature, with a ten degree difference between each zone. Thousands of plants have been keyed to these zones and most nurseries note the zone range for each plant they sell. The range is important, not just the lowest or coldest zone, because many plants have a requirement for some cold temperature in order to flourish. Tulips, daffodils, lilacs and most fruit trees, to mention a few, require a certain number of chilling days for their needed dormancy period or they won't flower or set fruit.
While the zones don't take into consideration local micro climates, knowing your zone and whether a plant is likely to survive the winter in it, is a good starting point. However, cold isn't the only factor that determines whether a plant will survive in our gardens. A plants ability to withstand heat is equally important.
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