It’s a confusing world out there these days. Even plants, arguably the most rooted of the Earth’s denizens, can be baffled by our changing environment, with balmy temperatures teasing them into emerging too soon, only to be hit by freezing blasts that frost their tender shoots. But the USDA, which just updated its Plant Hardiness Zone Map for the first time since 2012, thinks it has some answers.
The horticultural season is already underway—if you count the flood of catalogs clogging mailboxes, enticing the gardeners who peruse them in eager anticipation. But what plants will fit into our changing environment? Which of the delightful confections brightening the catalog pages will thrive in our yards?
The new Plant Hardiness Zone Map shows Northwest Connecticut now falls in Zone 6, where average winter lows can be expected to be between five and 10 degrees below zero. This is considerably warmer than its previous designation as 5, where lows of 20 degrees below zero were possible.
For gardeners, this shift might seem modest, but it carries considerable implications, especially in how it relates to the year’s first frost. Knowing when to expect that first frost—which often freezes and kills plants—is vital for deciding when to bring vulnerable plants indoors or when to prepare the garden for the changing season.
But a word of caution is in order. Nash Pradhan of Ginger Creek Nursery, a horticulturalist with more than 40 years of experience in Norfolk’s chilly climes, says he advises against “pushing the envelope” when using the new hardiness map to choose perennials.
“Norfolk is different because of all its microclimates,” he cautioned. “I’m not going to change anything. I will plant the same perennials, the same trees.”
The key to successfully raising plants is selecting the right plant for the right location and planting it correctly, he continued. “It depends on your location. What kind of exposure do you have? Are you in a valley? Are you near water?”
He now exclusively plants native plants, which have a high survival rate because they have adapted and thrived under local conditions for millennia. “I will not plant invasives or potentially invasive plants,” he said. “Burning bush has beautiful fall foliage, but it is so invasive that I removed mine 20 years ago and I still find seedlings in the woods.”
He admits that there is uncertainty about what the warming temperatures will mean in future years. “There are some rare plants that grow here. Will they disappear? We don’t know,” he said.
The rising temperatures have lengthened his season. “Things have certainly changed,” he observed. “There is almost no frost in the ground this year. I was still planting until the first week in January, when my season usually ends in late October or early November.”
But while the winter has delivered unusually warm weather, plants can still be affected by the variable temperatures. That late February day when he offered his insights to this reporter temperatures hovered around the 5-degree mark. And the lack of snow in recent years is also problematic as snow insulates plant roots, allowing them to withstand lower temperatures.
He suggested that gardeners who want guidance about what plants would do well in their landscapes consult with the Berkshire Botanical Gardens in Stockbridge, Mass., which offers a number of informative classes, or contact the UConn Home & Garden Education Center.