St. Louis is now Zone 7. What does that mean for spring planting?
We've gone from a 6B to a 7. It's not an average shoe size for St. Louisans but a clue to which plants survive winters in our gardens. The U.S. agriculture department has stated that changes in zones are not reliable evidence of global warming, as they are based on winter weather extremes. The department used better data from more weather stations for its cold hardiness map, which also indicates that about half of the country shifted to the next warmer half zone, while the other half remained in the same half zone. The botanical garden's climate garden tests plants recommended for warmer zones, which can cause them to become more sensitive to cold. The climate garden has also had success with plants deemed winter hardy, including a rosemary variety that survived two winters in the test garden.
Published : a month ago by jane henderson, Jane Henderson in Lifestyle
Some years ago, our area was actually a 5. Although the zone changes seem to indicate the effects of global warming, the U.S. agriculture department cautions that because the zones are based on winter weather extremes, "changes in zones are not reliable evidence of whether there has been global warming." It also explains that better data from more weather stations was used for the cold hardiness map.
It says that compared to its 2012 map, "the 2023 version reveals that about half of the country shifted to the next warmer half zone, and the other half of the country remained in the same half zone. That shift to the next warmer half zone means those areas warmed somewhere in the range of 0-5 degrees Fahrenheit ... "
"It's part of living in St. Louis. Everyone knows we have very erratic weather." The botanical garden's Kemper Center can also help home gardeners sort out new information. It has its own weather station and a climate garden where it tests plants recommended for warmer zones.
Still, the Kemper's climate garden has had some success with plants iffy for a Zone 6. A rosemary variety called Madeline Hill is touted as winter hardy. McKelvey says one has survived at least two winters in the test garden, but it was mostly brown on a recent March afternoon. Still, she saw a bit of green growing at its base.
When buying perennials, she recommends advice from the garden's own Plant Finder or from university extension services. If a plant is recommended for a range of zones, say 4-7, it should be fine if Zone 6 is in the middle of that range. This means that a plant recommended for Zone 6-10 is going to be more sensitive to cold.