What a frost at blossom costs

Damage occurs when ice forms in the tissue. Ice crystals growing in the spaces between cells draw water out of the cells and rupture membranes; the killed tissue then browns and collapses. In a flower the critical structures are small — the ovary at the base and the developing ovules within it — and the diagnostic check is straightforward: cut a flower or fruitlet longitudinally and look at the centre. A healthy ovary is pale green; a frosted one is brown or black.

Damage short of death has its own consequences. A flower whose ovary survives but whose ovules are partly killed will set a fruit with few seeds, which is likely to drop at June drop and, if it stays, to be small and misshapen. Frost also damages the fruit skin, producing the ring of russet around the calyx end known as frost ring — cosmetically ruinous for dessert fruit and irrelevant for cider.

The stage of development is what determines the temperature at which this happens, and the change is steep. The figures conventionally quoted for the main stages are given below. They are indicative rather than exact: how long the temperature is held matters as much as how low it goes, and a tree that has been hardened by cool weather tolerates more than one coming out of a warm spell.

The cost of a blossom frost is the whole year’s income from the affected block, against a cost base that barely falls: the orchard still has to be mown, pruned, protected and financed. For a grower with a contract tonnage to meet it may also mean a failure to supply, and for a mill it means finding fruit or juice elsewhere.

Higher-value fruit growing defends against this. Wind machines mix warmer air from above down onto the orchard; overhead sprinklers exploit the latent heat released as water freezes to hold blossom at around zero; orchard heaters, frost fans and covers all exist. Every one of them costs capital and running expense per hectare.

For cider fruit, sold by the tonne at a fraction of the price of dessert fruit, that arithmetic almost never works. Protection is therefore effectively unavailable to cider growers, and the defences that remain are the ones designed into the orchard decades earlier: a site with good cold-air drainage, and cultivars that flower late. This is the single clearest illustration of how the low value of the crop shapes every risk decision in a cider orchard.

A frosted orchard is not an idle one. Freed of a crop, the trees make vegetative growth and initiate flower buds abundantly in early summer, and the following spring they bloom heavily. If that bloom sets, the result is a very heavy crop, small fruit, and the beginning of a biennial cycle that can persist for years.

This is why regional cider fruit supply swings. A late frost that catches a whole county puts its orchards into phase with one another, and the glut-and-shortage pattern that follows is a physiological echo of one cold night. Mills manage it by blending across seasons and holding stock; growers manage it by planting cultivars with different flowering times so that a frost catches only part of the orchard.

For a maker, the year after a frost is a year of unusually plentiful but sometimes smaller and less concentrated fruit, and the year of the frost itself may simply not exist as a vintage. Both are worth stating plainly when a single-year cider from a known frost season is discussed.