German Study Finds Autumn Spray Can Delay Cherry Bloom and Cut Frost Damage

28 September 2026, Göttingen, Germany: Researchers at the University of Göttingen have shown that treating sweet cherry trees with the plant growth regulator ethephon in autumn can delay spring flowering by more than a week in some cultivars, a finding that offers orchardists a new chemical tool against the growing problem of frost damage to early-blooming fruit crops.

The study, led by corresponding author Wiebke Kämper of the university’s Department of Crop Sciences, was published in the journal BMC Plant Biology on July 9, 2026, and was highlighted again in a University of Göttingen press release on September 23, 2026, timed to reach growers ahead of this year’s autumn application window.

Why bloom timing has become a bigger problem

Fruit trees such as cherry and apple have been flowering progressively earlier over recent decades as winters warm, but the risk of a late, sharp frost after bud break has not gone away at the same pace, leaving orchards more exposed to a mismatch between early bloom and lingering cold snaps. A single hard frost during or just after flowering can destroy most of a season’s crop, since frozen flowers and young fruitlets typically do not recover. Growers have few practical options for delaying bloom itself, as opposed to protecting already-open flowers with methods like overhead sprinklers, wind machines, or heaters, all of which are expensive and only partially effective.

Ethephon is a widely used agrochemical that breaks down inside plant tissue to release ethylene, a natural plant hormone involved in fruit ripening, leaf drop, and dormancy signaling. It is already registered for various uses in fruit production, including thinning and ripening applications, which makes a bloom-delay use case a comparatively low-hurdle addition for regulators and growers already familiar with the chemistry, rather than an entirely new active ingredient requiring fresh registration.

What the trial found

The Göttingen team applied ethephon at two concentrations, 500 and 750 parts per million, at two timing points in early and late autumn, to two sweet cherry cultivars (Bellise and Kordia) and two apple cultivars (Elstar and Kanzi) growing in German orchard trial plots. Researchers then tracked the proportion of flower buds in bloom on multiple dates the following spring and measured how much fruit ultimately set on treated versus untreated control trees.

The results were sharply cultivar-dependent. In the Kordia cherry cultivar, control trees reached 88% of flower buds in bloom by April 9, compared with only 56% in trees given an early, high-concentration treatment and 63% in trees given a late, lower-concentration treatment, a delay large enough to meaningfully shift a tree’s bloom window relative to a frost event. However, this delay came at a cost in that specific case: the late, high-concentration treatment on Kordia also cut final fruit set from 16% to 6%, showing a real trade-off between how much bloom is delayed and how much fruit ultimately forms. In the Bellise cherry cultivar and both apple cultivars tested, ethephon produced no significant flowering delay at all, indicating the response is not a general effect across fruit tree species or even across cherry varieties.

The practical implication is that ethephon-based bloom delay is not a simple, one-size-fits-all frost insurance treatment. Growers and their agronomists would need cultivar-specific data on both the degree of bloom delay and the fruit-set penalty before adopting it commercially, and the researchers frame their results as an initial demonstration of feasibility rather than a ready-to-use protocol. Further work is likely needed to test more cultivars, more climates, and multiple growing seasons before the approach could be recommended at scale.

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