Frost/Freeze, Weather and Gardening

Transitioning from winter to spring and summer to fall are the two times we expect to experience frost/freeze and the corresponding potential damage to plant tissue -- think of it as the dramatic change going into and coming out of a rest/recovery period, much like sleep. But way too many people (I have no doubt it is most) allow themselves to be convinced this weather event can be reliably predicted (i.e., in a calendar sense, like celestial cycles). It is NOT and cannot be. Wishful thinking. Here's why not. First, our weather records go back only to the 1880s. In fact, daily forecast meteorology started in the mid 19th century (1854), having been pioneered by Robert FitzRoy, not surprisingly a sailor who, you may be shocked to learn, was the captain of the HMS Beagle, the ship that transported Charles Darwin on his famous voyage of discovery. Further, if we were to include the first half of the 19th century the records would factor in the catastrophic aftermath caused by the explosive eruption of the Indonesian volcano Mount Tambora in 1815 which resulted in 1816 being referred to as the Year Without Summer. The prodigious quantity (est. 10 cubic miles of solid material) that was blown into the atmosphere caused a volcanic winter effect. In 1816 it frosted or froze every month in the Midwest -- no actual growing season, but more on that later.

Fast forward to the weather forecasts of today. We have advanced the technology and predictive ability remarkably, but (1) what will happen in the future is still only an educated guess and (2) what and when something happened last year has little to no bearing on what or when it might happen this year, or the next. It's called the Law of Independent Events, like flipping a coin, in this case a many sided coin. Yet when the self-assured forecasters give us the prediction most of us willing accept it as a certainty, as gospel. We want to believe it, hope its possible. Yes, THE AVERAGE the oracles provide is useful but it is FREQUENTLY wrong. For example, I recall hearing the most popular local forecaster say on the 6 o'clock evening segment a couple of years ago in July that the high the next day would be 88 degrees (F). The high was in fact just 66 -- off by 22 degrees even though the confident foretelling was made less than 24 hours in advance and with the aid of advanced predictive modeling provided by the National Weather Service. She was wrong, way wrong. If the forecasters have an annual professional meeting, the top award given might best be called the Nimbus Least Wrong Award :)

Too often the weather forecasters say "it's supposed to be" when in fact we will not know for sure until it happens -- it's called reality -- and I recently heard that weather forecasters are highly trusted by the public. I find this confidence perplexing given how often the prognosticators are wrong, and don't try to tell me you haven't heard it before. Yet one can find online claims (by meteorologists) that they are 80% right even on 5-day weather forecasts. I track this and would be willing to take that bet, assuming they want to stick with their precise guesses. I have a couple of Benjamins ready for the wager. I suspect the 80% correct claim is made with the idea that 82 and 84 are counted correct if the call was 83, perhaps even 81 and 85. Try collecting on a near miss at the casino. I have said many times, we would be better served and the ordained weather gods would be better off giving a range statement (e.g., low 80s, mid 80s, high 80s) rather than a specific targeted number. Moreover, the predictions about precipitation are even less accurate.  Jupiters they are not, although I get the feeling that the lauding has caused some of the guessers to think they have special insight, beyond what training and experience allow. Comments like "watch what I have in store for you" implies such power. And regarding long-range forecasts, 8-10 days out is about the max and speculative, perhaps 50/50. All we should count on being dependable for long-range are general suggestions based on seasonal changes. See also my Feb 2020 Farmers' Almanac Predictions blog posting. Finally, our climate is changing so rapidly that when providing averages we (especially gardeners) should concentrate on the results from "since the change took hold (1990s)" as well as focusing on the anomalies, especially going into and out of winter. And soil moisture, which mirrors organic content and regulates temperature, is overlooked as a weather and climate regulator. But I digress :)

Earlier I introduced growing season. I was stunned when told that a current biology professor at Indiana University was unfamiliar with the concept. How can anyone, never mind a Ph.D. biologist who has lived in an agriculture state for decades, not know? Obviously the fellow is not a gardener. Those of us who are know that growing season is the number of days (the period) between the last freeze of spring and the first freeze of autumn in any given year and remember that it varies by region and even within a region. When I say freeze I am referring to an air temp of 32 degrees Fahrenheit, but know that in certain circumstances ice crystals can form a few degrees above 32 or it may not freeze at 32 degress. Again, like the daily averages calculated from days past, the growing season is NOT a fixed number. I keep and have analyzed gardening related data for my area (central Indiana) over the last half century and can tell you that the mean growing season has been 189 days, but the range is 62 days (153 - 214). The shortest was in 1976 and the longest in 2016 and 2019 and, for those interested in such things, the median was 184 and the span was modeless since several dates occurred multiple times but none more than twice. Furthermore, there was not and is no relationship between what happened the previous year nor does when the start (last spring freeze) occurs affect the stop (the first fall freeze). Moreover, when the last (spring) and first (fall) freeze occurs is NOT A RELIABLE CALENDAR EVENT DATE like say lunar cycles or an eclipse. Never has been, never will be! It is NOT preordained! For examples, in central Indiana over the last five decades the average date for the last spring freeze has been April 17 but it has NOT occurred on that date. Yes, on 20(3), 19, 18(2), 16, 15 and 14(2), but not the 17th. The earliest date during this 50-year span was March 24 (1998) and the latest May 19 (2002), for a range of 56 days, but not the 17th. For the first freeze of fall the average has been October 19, but that happened only one (1988). By comparison, the range for the first fall freeze has been only 44 days. Again, the average is meaningless with respect to what will happen the next year. Know that when the 50 years is halved, profound differences are evident, among them the mean maximum low temp was much higher during the most recent 25 years. I maintain an ALMANAC on this website which has climatic info and other gardening related data. It is useful and a good idea thus I am surprised other people and places have not done something similar, as the data could be very useful in the short- and long-term. I tried a couple of times to get my state's main agronomy school (Purdue) interested -- crickets. How plants interact with the environment is far more complicated than the average temperature and rainfall.

FUN FACT: In case you were thinking of placing a bet counting on April 17 and October 19 to be better winning choices, since they have hit so infrequently, you would be wrong. It's called GAMBLERS FALLACY and relates to the previously noted Law of Independent Events. Past events do not influence future outcome. The likelihood you would hit are more like one in 56 for spring and one in 44 for fall, but even those numbers could increase. Bottomline, (1) Objective reasoning and rational action should be the norm but most people (including gardeners) are frequently unable.  (2) Larger sample size can show trends but not dependable calendar dates. And (3) weather people should rethink and be careful about what they say (especially use of the verbs should and will), perhaps giving an occasional lessons on some aspect of weather, climate and forecasting (take time from the sports segment that day) since the public is woefully deficient regarding environmental issues, not just meteorology.

Here are some factors that gardeners need to know regarding frost/freeze:

1. moist soil will help prevent damage (due to the thermal capacity of water, its ability to get and store heat)

2. wind can and will help prevent damage (by mixing the air, preventing cold pockets from forming)

3. humid air usually produces more frost (more water vapor for freezing) and know that freeze can happen without frost

4. plants in lower areas are more prone to damage (convection causes cold air to sink)

5. frost (surface) and freeze (internal) can occur at temperature above 32 degrees F when suitable conditions exist

6. poorly sited specimens can be more affected - again, plants in low lying areas and (in spring) species that naturally open early if planted against (on the S side of) buildings are susceptible (are forced to open too early (solar thermal load inducement)

7. hard or killing frost - when the ground temp drops to or below freezing -- but bear in mind ground temperature has a delayed thermal response (i.e., after the spring freeze) as well as after the fall atmospheric freeze, but since the ground stays warm the roots will continue to grow

8. previously stressed specimens are more susceptible

9. covering plants can sometimes prevent damage from cold temps but the covering and uncovering is burdensome and often results in mechanical damage, plus if the temp is more than a few degrees below freezing covering may not help; I would instead recommend watering the ground below the plant(s) and then yourself with a stiff one (to pacify the anxious gardener) and keep it mind, in the fall it is going to happen soon regardless

   
   

PLANTS SENSITIVE TO FROST -- damage occurs because ice crystals form in the cells which rupture the cell wall. Examples include: Solanaceae (e.g., peppers and tomatoes), many mints (Lamiaceae, e.g., basil, but usually already gone {extracted} at my place long before frost), okra (Malvaceae), cucurbits (squash/melons), Kentucky coffeetree, oriental maples, goldenrain tree, black gum, Bignoniaceae, primarily a tropical family (e.g., catalpa and trumpet vine), early flowering species (esp. some magnolias), ALL tropicals, anything in the vulnerable stage (not hardened off)

(top pic SPRING) star magnolia which has suffered tepal tip damage, the function (reproduction) was not affected -- let me suggest that if one can get past the fact that the brown represents damaged/killed tissue, it is hard not to see the rich brown with pure white combo as beautiful

(bottom pic FALL) taken the day after the first fall freeze which causes all the leaves of a catalpa to fall within hours, much like the more well known quick drop of ginkgo leaves later in fall, and the catalpa drop can be no less dramatic

PLANTS TOLERANT OF FROST AND FREEZE -- less susceptible because of solutes (salts & sugars) and protein concentration buildup that dramatically decrease the freezing point, acting like a type of antifreeze and/or because of morphological modifications (e.g., surface covering, thickness, shape, etc.). Examples include: green onions, leaf lettuces, Swiss chard/beets, hardy evergreens, members of the sunflower family (Asteraceae, like cardoon/artichoke, marigolds and mums), members of the carrot family (Apiaceae, like celery and parsley), members of the mustard family (Brassicaceae, like collards and kale)

For more weather and climate information relating to plants and gardening see Chapter 12 in my Rantings book and/or my March 2020 blog. BTW, the high tomorrow will be . . . :)

Oops, I violate my 10,000 character max.