Changing Zones

Moving from a house in San Jose, California, to an apartment in downtown Seattle, Washington brought many changes to this gardener’s life. Raised beds, fruit and nut trees, and many of my larger plants had to be left behind. Potted herbs came along, and they seem to be enjoying balcony life. But temperatures are dropping. It was time to learn more about my new USDA Hardiness Zone. What I learned surprised me.

Seattle tree badly sunburned (Kate Russell)

Normal changes

It’s not unusual to discover that a new location has a different set of conditions related to gardening. The weather is certainly different. I went from a scorching hot, drought-prone climate to cool, overcast skies and a lot more greenery. The soil situation is very different. My heavy clay made better with wood chips must now be replaced with bagged potting soil. Instead of a compost pile for plant food, I will be using store-bought fertilizers. I’m sure there will be new pests and diseases to contend with, but I haven’t run into them yet. The biggest surprise for me, and one that affects all gardeners, was the change in Hardiness Zone.

USDA Hardiness Zones

The USDA Hardiness Zone map divides the U.S. into zones based on average winter low temperatures. Understanding these zones helps gardeners select plants that will thrive. The 1990 map, which I have been using for years, told me that my San Jose garden was in zone 8. The more recent 2012 map says it’s in zone 9. The same shift is true of Seattle. The older map puts Seattle in zone 7, while the newer map says 8. More on that in a moment.

Each zone is divided into 10°F increments. That means temperatures, as far as gardening goes, have risen profoundly in recent years. Before you panic, you need to know that some of those changes are due to better science and improved measurements. But temperatures are changing. Temperatures are critical in determining what will grow well and what will struggle in your garden.

​Global zone issues

Back to Seattle. This past summer, there was a week with temperatures around 110°F. For anyone familiar with Seattle weather, you will know that this is unheard of. As we drove along I-5 to our new home, we could see the damage caused by those temperatures. Trees exposed to the afternoon sun were badly bronzed. Extensive sunburn damage can be seen everywhere. These plants were not able to protect themselves against the unusual heat. Many trees will die as a result.

Seattle trees shaded by buildings were protected from sunburn (Kate Russell)

This type of damage is occurring in food production around the world, too. An article published by Science Daily tells us that fully one-third of the world’s food crops are at risk because of climate change. Master Gardeners, farmers, and researchers around the world are trying to find out what works and what doesn’t under these new conditions.

What changes, if any, have you seen in your garden over the past few years? Have temperature changes altered what and how you grow?