New USDA Plant Hardiness Zones
I have not agreed with the changes to the hardiness zones by USDA, and now it has caused some issues for gardeners.
In 2012 USDA changed the plant hardiness zones to reflect the latest 30 year average. The problem I saw, and still see, is that the weather we are seeing in the Midwest is not necessarily warmer consistently. We are definitely seeing more extreme weather. Understanding averages and statistics gets complicated and clearly the extreme highs have raised the average.
But I see a fatal flaw in the logic of changing the zones based on the change of averages. The lowest temperatures experienced under the previous zones assigned still exist, if not worse. The extremes we have seen are frequently with longer warmer autumn and the longer growing season is really wonderful But the extremes surface also in the low temperatures, and that is what kills our plants in the north and Midwest. So, changing the zones does not change what will survive our winters.
Now the real problem shows itself. We have just come through, actually we are not even through it yet!, a winter of extreme cold with little or no snow cover during some of the coldest temperatures. And now the Midwest is struggling to get out of winter and we are well into April. Temperatures every single day have been below average and we have, hopefully, finished record breaking snow for the month.
Previously, no plants shipments are made into my region until May 14. This year, of all years, at least one Midwest nursery decided to make shipments according to the new zones. My plants were shipped from an Ohio nursery on April 11, literally 24 hours ahead of an enormous blizzard with warnings across the midsection of the country. I don't know what rock they were living under that they didn't have more sense than that in the first place, but our frost free date is still May 14 around here regardless of changes to the map. Now I have plants that got caught in a blizzard, sitting in unknown conditions in the back of a truck for 11 days, that I have to nurse along for another month before I can plant them.
It does appear that the perennials were frost damaged but it is difficult to determine what conditions caused damage. It may be possible to salvage the perennials but the results will not be known until they are cared for the next few weeks, hardened off, planted, then nurtured well into summer. If at that time they fail, well, that is a lot invested for bad shipping dates. And according to Classic Caladiums, temps in the forties and fifties can adversely affect caladium bulbs, even though they are dormant. Since it is likely the shipment was exposed to much lower temps than that and perhaps for many days, the caladium bulbs are probably not viable.
Be warned, check the shipping policies of mail order nurseries. Some have changed dates, some have not, and some do allow YOU to select a date range for shipping. Ok, I'm done ranting. It would be interesting to know if this has become a problem for others.