Cold temps and possible crop damage?
Phil Forsyth
Wondering about the freeze predicted this week and possible effects on your blooming fruit trees?
From: Mike Biltonen from Radical Pomology! <knowyo...@substack.com>
Date: Mon, Apr 7, 2025 at 6:53 AM
Subject: The Danger Zone
To: <ph...@phillyorchards.org>
Warning: Sleepless nights ahead! Well, that time of the year has arrived, again. That one where fruit trees and vines¹ may be just far enough along to where any unreasonable dip in temperatures causes a certain anxiety in some, sleepless nights in others. It was just two years ago when the temperature dipped low enough on May 18 to cause widespread fruit tree crop losses across the entire northeast. Last year, thankfully, was a successful rebound with no serious threat of crop losses due to cold temperatures or frost. This year, with return bloom down (due to large crops and biennial bearing) and growers looking for some consistency from year to year, to have consecutive cold nights headed our way is just a bit disconcerting. Not worrisome per se (there isn’t a real threat this week), but just a not-so-gentle reminder that we have at least six weeks to go before we can relax, somewhat.
Image: Apple blossom affected by frost on May 18 2023. Variety unknown. Hector, NY Critical Temperatures. All tree fruit, grapes, and small fruit have cold temperature thresholds below which their fruit buds can’t survive. It isn’t all black and white, and depends on many factors, primarily phenological stage. But genetics, age and health of trees, previous year’s crop, how quickly did the temperatures drop, how long did the temps stay at their lowest, how quickly did they rebound, what were the conditions before the drop? Almost all research has been done around phenological stage, so it requires each grower to use their internal “processor” to adjust risk based on YOUR conditions. Michigan State has a great page where you can “see for yourselves.” Bear in mind that this work was done in a lab and not under field conditions, and needs to be updated under current climactic pressures.
Apples. Most commercial dessert apples in eastern NY are at quarter-inch green (QIG), while some crab apple varieties are further along and most European cider apple varieties are still far behind. This means that some crab apple varieties (probably species dependent) have unique phyto-protection against frost damage when in bloom, while late-blooming cider apples can provide a modicum of protection against cold temperature damage or frosts simply by developing later than your average apple². If we use the average current phenological stage, then we’d need to have temperatures of 23F (-5C) to result in a bud kill of 10% and 15F (-9.4C) for 90% bud kill. Its safe to safe to say that for this week at least, we’re safe - but there’s a long way to go³. Genetics seems to be one of the most interesting paths to take when considering a frost- or cold-resistant orchard. And while avoiding early blooming varieties and considering late-blooming cider varieties seems pretty obvious, there are some less obvious considerations to make. For example:
Each of the crab varieties probably has some interesting inherent genetics that give it this resiliency. Many varieties with the less resiliency were probably bred and/selected from chance ‘natural’ crosses when the climate was less chaotic. So considering the background genetics of any variety before planting is a worthwhile endeavor. Chris also added that he uncovered that at least Golden Hornet = Malus sieboldii x Malus prunifolia and Hewe's Crab = Malus angustifolia x unknown variety have some unique parentage. Undoubtedly others many do as well. So there’s lots to investigate!
Image: Golden Hornet tree with fruit after enduring cold temperatures/frost just a few months earlier. Courtesy Chris Negronida, Perry City Orchard and Nursery. Stone Fruit. Stone Fruit⁴ though are more sensitive since they tend to be more advanced than pome fruit at the same time of the year. Fortunately, the forecast still doesn’t suggest we’ll do more than flirt with disaster. Apricots - the furthest advanced of all stone fruit - need to see temperatures of 22F (-5.5C) for 10% bud kill and 9F (-12.8C) for 90% bud kill. Though there are differences, all stone fruit are more or less equally sensitive at the same phenological stage, some just progress faster than others.
The Bottom Line. The bottom line is that we have a long way to go. It used to be that Mother’s Day was the last date where we had to worry about late frosts. However, I am now considering that 1 June is a more appropriate date. But, of course, with climate change being a serious issue confronting farmers of all types, “all best are off” as they say. I will monitor the low temperatures for all of Know Your Roots’ client sites and report back later this week. But lowest of lows will be within 2-3F of doing only 10% damage. We should be fine, but still have six weeks to go. But what can anyone do about it? I mean, nature is nature, right? Well, there are steps one can take this early in the season. But from my vantage point, cold temperature and frost prevention is something that starts the year prior. Stay tuned for Thursday’s newsletter on Cold Temp and Frost Prevention Techniques. 1 grapes have yet to break bud so are still relatively safe. 2 For the purposes of this article, your average apple variety is the ubiquitous McIntosh. 3 Pears are very similar to apples, in case you were wondering. 4 Peaches, apricots, plums, and cherries You're currently a free subscriber to Radical Pomology!. For the full experience, upgrade your subscription.
© 2025 Mike Biltonen
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