Polar vortex in May? Looks like it. You may want to hold off planting those tender annuals.

Garden centers have been buzzing with activity this spring and flowers and  tender vegetables are flying off the shelves and into the ground. We are past the “official” last frost date in Cincinnati, right? Time to plant tomatoes, peppers, and impatiens, right?

Well, not so fast. Mother nature didn’t get the memo that the climate is warming and doesn’t recognize the warmer USDA hardiness zones and last frost dates. I have been saying all along that warming everything up was  unwise. We may see why this year.

You know that polar vortex which was absent from the US and tucked away in the arctic this winter? Well, it appears set to make a rare and unusual May appearance. Widespread frosts and some freezes will come down into the Great Lakes and New England and may even visit the Ohio and Tennessee valleys over the next couple weeks. Temperatures will fall well below normal all the way down to the gulf coast. There may even be some May snow in the Great Lakes and New England.

So, if you have been waiting to plant your tender plants, I would wait some more. If you have them in the ground, good luck. You heard it here first. The cold train is already pulling into the station with the coldest air expected this weekend. Temperatures will only slowly moderate after that (Revised last paragraph on 5.5.20200).

9 Replies to “Polar vortex in May? Looks like it. You may want to hold off planting those tender annuals.”

  1. Mother Nature doesn’t need the memo she creates the memo. It’s those of us planting that should be mindful of long term cyclical weather patterns like grand solar minimums

  2. I do not think that this map interpretaion is correct. For the periood indicated the map doesn’t precict a polar blitz but rather that the temperature will either be above or below normal.
    The dark blue area thus tells us that in those regions there is a 90% chance for the temperature to be below normal but doesn’t say how much below average it will be.

    1. Multiple other sources including NOAA are predicting a cold surge with near record cold in parts of the east. Frosts and freezes are likely at least as far south as the Ohio valley this weekend and possibly locations farther south. Remember, this is May. A lobe of the polar vortex pushing down cold air is still going to be modified by the warming sun angle and lack of snow cover. My post is a restatement of discussions from meteorologists. I do not make my own forecasts. I am an arborist. I draw on information, forecasts, and analysis from meteorologists. My degree includes environmental interpretation so I tend to be able to explain complex set ups in terms people can understand. As for how below normal it will be 20-30 degrees below normal for some.

  3. I see the two other links, but can you please provide the link to the NOAA page you took the screenshot from?

  4. Here in Central and northern Maine we don’t put anything in the ground until after the the full moon beginning of June. Even that’s been tricky in the past. We had a frost one year in June that wiped out all the new oak leaves on the trees in certain areas of the state. All my perennials and anything in the ground have a ready stack of straw mulch right next to them just in case.

  5. In the Cincinnati area it is better to wait until after Mother’s Day at the earliest to plant tender annuals. I wait until after the 15th to be sure we aren’t having a cold night where I have to cover everything.

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