Erratic Effects of Spring Frost


Here are two stalks of asparagus growing just a foot apart. Both are of the same thickness and height. After an early morning temperature of 28 degrees F, one stalk is frozen and one is not.  I have seen this happen many times. Anyone know why?

This spring, when temperatures went from ridiculously high levels much of winter and early spring, and then plunged on some nights in late March and early April as much as fifty degrees in 24 hours into the twenties, fruit farmers are at their wits’ end. Early warm weather usually means lots of killing frost later on. One market gardener told me a month ago while we were both enjoying our lovely blossoming trees that I could kiss my peaches goodbye for this year.  I thought so too, but strangely, against all odds including at least seven nights of below freezing weather since then, I still have peaches. Trying to figure out why provides a whole bunch of observations about frost, none of them suggesting anything conclusive except that official weather reports of the highs and lows for the day don’t always apply equally to every local area within the reported area.

So many factors influence frost killing that I doubt actual official temperatures are very meaningful. Sometimes the slightest little change in one farm’s micro-climate compared to another can make a huge difference. I don’t know for sure why my peaches survived. First of all they got through winterkill, the usual destroyer of peaches here, when a couple of warm days in January or February can cause buds to swell. Then really cold weather kills them. Having survived that, most of all because it never got really cold, these peach trees came into full bloom in early March, a month ahead of schedule. The warm spell lasted six days, enough so that the flower petals began to fall, and the tiny little peaches form.  These little peaches, however tender, can withstand a degree or two more of below freezing weather than open blossoms. (Professional peach growers say, even in bloom stage, a peach tree can handle 4 hours of 27 degree F weather but no lower or longer.) Not all the peach blooms survived. Some died and fell off, but the trees were overloaded with blossoms anyway, so that was good.

My trees are surrounded by large forest trees and grow next to the barn buildings. The trees can keep the temperature a degree or two warmer in their immediate surroundings, so experts tell me. Also barn buildings give off a bit of heat during the night that they absorbed from a preceding sunny day.  That’s why some gardeners espalier peach trees to the sides of their houses or against rock walls. Another frost protector is wind. Wind motion can literally blow frost away which is why in eastern Pennsylvania you find commercial peach orchards on steep mountainsides where one would think frost would be inescapable. At night, cold air sinks pulling warmer air higher up the mountain slope down through the orchards to fend off frost. In my situation, a northerly wind at night can sometimes keep frost away even at below freezing temperatures. Another frost defense is a large body of water nearby. Fruit orchards flourish along Lake Erie because the lake effect can keep the frost away that causes mischief farther south. I wonder if fruit trees avoid frosts if grown on the banks of farm ponds.

Frost effect can be exacerbated by mulch. In my earlier, innocent days I over-mulched part of my garden too early in the year—in May. Sure enough we had a late frost and it killed the squash plants that were heavily mulched but not anything where I had not yet mulched.  The mulch had prevented the warmth of the soil from rising up and fending off the frost.

All well and good, but none of that explains one frozen spear of asparagus just a foot away from an unfrozen spear. I like the mystery of it. If we knew the answer to everything, life wouldn’t be fun anymore.


Gene, I observed your farm pond theory in action when I worked as a loss adjuster/field tech for Farm Services Agency a few years back. I was sent out to the same orchard two years in a row that had lost its entire crop to frost. The trees were essentially bare, all except for the northern spies that grew along the edge of the farm pond…

I suppose keeping a farm pond around has more advantages than one might think. Apple pie, no matter the weather.

You could be seeing slight varietal difference in cold hardiness? Another aspect not to forget is the living soil food web. I’ve seen more biologically active soil to warm up faster in the spring and not suffer the affects of drought and heat as hard. This could also play into the previous posters comment on sugar levels.

This may be one explanation for your thawed vs frozen asparagus: maybe the spears have different levels of sugars in them. Next time you observe the phenomenon, taste each spear to see if one is noticeably sweeter than the other and let us know! Cold-hardy plants put more sugar into their cells when it’s cold – it’s antifreeze! I never really understood the whole thing about spinach and brussels sprouts being “sweeter after a frost” until I started growing lots of kale. Then regular tasting informed me that the frost per se has nothing to do with it, but extended cold temperatures do.

P.S. I think my sour cherry crop is doomed this year. I hope I’m wrong.

Gene, in addition to the microclimate effects you describe, endophytic bacteria living inside plants can provide frost nucleation sites and catalyze freezing at warmer temperatures than a plant with fewer or no endophytic bacteria. Some people recommend spraying with copper sulfate a couple days prior to frosts to protect plants. I used to grow grapes in Minnesota, so I tried everything I could think of. Endophytes are not all bad for plants. I would like to see your observations on them. On-going research is evaluating these as biopesticides; I could send you a recent paper if you are interested. Actually, I think this is potentially very important, and controversial, especially in Mendocino County where I live, because some of the work blurs the line between conventional breeding and genetically modified organisms. I would love your take on that aspect as well. Peggy

    Peggy, I confess I know nothing from experience about endophytes. What you say sounds very interesting. I do have opinions about coventional breeding and genetically modifed organisms. In some cases the difference is not much, in my opinion, which is why I have not been outspokenly against genetic modification. I have monkeyed around with open pollinated corn for years. i am genetically modifying that corn. However I am not trying to insert genes from other species into the corn. That is where I think Monsanto is playing with fire. Gene

I’ve wondered the exact same thing about our asparagus bed. Have I done something wrong? Too much mulch? Not enough manure this year? However, I like your explanation the best, and I’ll just leave it a mystery.

Great post, Gene. You hit on a few points I identified with.

First of all, one of the local TV meteorologists out of Portland, Oregon runs a nice little blog in which he comments on the weather in more depth. I really like this guy–he’s right more often than not and on the blog he’ll get into a lot of technical details that he doesn’t in the broadcasts, some of which I understand and some not (I really don’t understand the technical weather modeling and such.) But one of his pet peeves is forecasters who will give snow levels to, say, 700 feet or 600 feet or something like that. He basically won’t give anything more specific than 1000 feet and instead qualify that you may or may not see snow depending on your location (for a borderline snow situation, obviously, that isn’t going to see just a big snow storm all over.) His point is that you can’t say someone at 600 feet is going to get a couple inches of snow while someone else at 580 isn’t going to see any. That may happen, but it could just as easily be the other way. It’s all dependent on micro climates and such, and micro climates can get very micro indeed.

As for mystery, I much agree with you on that. I enjoy the mystery, as well. Wendell Berry’s Life is a Miracle is one of my very favorite books and one of the main themes in there is the importance of mystery–that we need it, as humans, to realize that we will never fully understand the world, can thus never control the world, and must therefore stay humble and act with care and caution. That’s a lesson we really could stand to learn as a society and culture.

“If we knew the answer to everything, life wouldn’t be fun anymore.” Amen. As an engineer, I love figuring out how/why things work. The wonderful thing is, no matter how much we think we know, there always seems to be a deeper mystery. I need no other ‘proof’ of the Creator.

Jack Frost clearly has a sense of humor.

Our local weather guy suggested that the wind kept the frost from doing too much damage. Indeed it was cold (24ish) but we had no frost – it blew hard through the night.

Gee thanks, now I think I put our orchard on the wrong side of the greenhouse, as it is the greenhouse that is next to the pond for easier watering. I still have my trees under wraps here in Latvia, as our temperatures are still getting down rather low at night, but I think I will have to take a look again at how we mulch and position our plants. Thanks for the insights and the reassurance that we can never get it totally right anyway.

Re. peach trees and freezing, see Robert Frost’s exquisite little poem THERE ARE ROUGHLY ZONES. It ends: “if it is destined never again to grow,
It can blame this limitless trait in the hearts of men.”

I so enjoy your observatioins, Gene.

Ed Searl

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