In the Garden:
These Himalayan blue poppies are rated hardy in USDA Zones 7 and 8, but they're thriving in a Zone 4 garden in Quebec.
Can You Trust the Zone Map?
I fell in love with Meconopsis the moment I saw her photo, tucked in the pages of a seed catalog. Who wouldn't love this beauty, with her alluring sky blue flowers and delicate, fuzzy, nodding buds?
I've learned to be cautious about promising my heart to just any old plant. How many times have I been smitten, only to find my new love is not suitable for my climate? In this case, however, the catalog gives Meconopsis betonicifolia, the Himalayan blue poppy, a rating of USDA Zone 7 to 8. Time to celebrate? Not quite.
Several years ago I visited the famous Metis Gardens (Les Jardins de Metis, also called Reford Gardens) on the Gaspe Peninsula in Quebec, and to my amazement there were thousands of blue poppies in full bloom! I learned that this wasn't a fluke -- Metis is famous for its Meconopsis.
How could this be? I would think that even with the moderating effects of the St. Lawrence River, Metis is no warmer than USDA Zone 4. So why does Meconopsis not just survive, but actually thrive there?
Limitations of the Hardiness Map
Meconopsis offers a perfect example of the limitations of the USDA Hardiness Zone Map. The map divides the country into zones based on one statistic: the average minimum winter temperature. Meconopsis, rated to zones 7 and 8, would then theoretically thrive in places as diverse as Raleigh, North Carolina; San Antonio, Texas; Las Vegas, Nevada; and Seattle, Washington. Of that list, where will Meconopsis grow reasonably well? Only in Seattle.
Meconopsis cares less about the minimum winter temperature than it does about summer temperature and moisture. The plant thrives where summers are relatively cool and moist -- places like the Pacific Northwest, for example. And places very much unlike the other cities mentioned. So the hardiness rating of Zones 7 and 8 isn't particularly useful for determining where this plant will grow.
The USDA Hardiness Zone Map is just one tool for determining whether a plant will thrive in your region. There are also other zone maps, including the Sunset Map (most useful to gardeners in the west) and the Heat Zone map (most useful where soaring summer temperatures can damage plants). You also can consult with local horticulturists, refer to plant lists at nearby public gardens, or look in regional plant catalogs. Do some research on the plants you want to grow to determine their native habitats, which can give clues to cultural requirements.
For example, the Himalayan blue poppy, true to its name, is native to the mountains of China and Tibet. It's found in moist alpine meadows at altitudes of about 10,000 to 13,000 feet. While there are few places in the US that mimic that environment, there are areas that provide the cool summer temperatures, filtered shade, and moist, acidic soil Meconopsis enjoys in its native habitat.
Unfortunately, our region isn't one of them. Even though the USDA zone map indicates otherwise, I don't think the Himalayan blue poppy stands a fighting chance in my yard. The summer sun and heat are just too intense, and the winter temperature fluctuations are too great. I guess I'll have to settle for a road trip to Seattle or Quebec!
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