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Saturdays in the Garden: Hot Enough for Lemon Trees Beyond the Tropics?

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When life gives you lemon trees, make lemonade!

tiny lemon trees in container with flowers in background

A couple of years ago, it was fascinating to see the United States Department of Agriculture shift its reliable Plant Hardiness Zone map to reflect a warmer climate for much of the United States.  In our area of East Tennessee, we shifted from a 6b to a 7a, with some of the state shifting into the 8 growing zone, feeling closer to the weather in North Florida.

I’ve always admired how friends in sunny Florida could grow their own citrus and wished I could have my own lemon tree in the backyard.  So, I saved seeds from an organic lemon and started my own, tiny lemon trees last summer.  I managed to keep four of them alive indoors through the winter.  In their second summer, one of the plants has shot up into what I can imagine producing fruit in a couple more years.

USDA Hardiness Zone map

To keep my baby lemon trees alive in Tennessee, I’ll need to transplant each into its own container, provide proper drainage, fertilize regularly and shelter them indoors between mid-October and mid-March. Of course, I don’t hold much hope for tremendous citrus orchard success just yet in my area. Lemon trees prefer Zone 9 or even warmer.

Since the USDA Hardiness Zone maps average the lowest winter temperatures over a past time period, the most recent covering 1976-2005 temperatures, it’s possible my garden is already getting warmer in the summer than the map reflects.  It seems we’ve been experiencing longer and longer growing seasons in my area with more hot, humid days that require attention to preventing mold or blight in the garden.  The National Climate Date Center reports we’ve had the fourth warmest July on record in 2014, although the US has also experienced some cold extremes in recent years, another reminder to bring those plants indoors this winter.  A cold snap late last winter even killed my typically winter-hardy rosemary, so those lemon trees wouldn’t stand a chance.

Where can gardeners look to stay even more up-to-date than the USDA data?  There may be hope in scientists using data tools to predict future growing zones.  The National Aeronautics and Space Administration has announced that Abdal Elhassani of Indiana University has an award-winning idea for an app to predict how plant hardiness zones will change along with our changing climate.  NASA is promoting the OpenNEX project to promote creative uses for climate projection using large sets of data. There’s even a $50,000 prize up for grabs for the best climate app!  Imagine the technology to help home gardeners and family farmers avoid losses from drought or floods, or the data to better predict wildfires.

Maybe you can grow something you never thought possible before in your garden.  Connect here with an interactive version of the USDA Hardiness Zone map.  I’m anticipating some tasty lemonade on a hot July day!


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