In Chaharmahal, Azerbaijan, Hamadan and Khorasan, irrigate before the frost, whitewash the trunks of saplings, put up a windbreak, and postpone heavy pruning through the peak of the cold.
Winter in Chaharmahal and Bakhtiari, Azerbaijan, Hamadan, Kurdistan and many plains of Khorasan is not merely cold; it is a combination of night frost, harsh midday sun on a dark trunk, dry wind and sometimes frozen soil with no stored water. A tree that enters that combination in autumn with heavy foliage and dry soil suffers more than the absolute cold would explain. Winter preparation is not the showy business of covering the whole orchard in plastic. The precise work is to supply moisture to the roots before the soil locks up, to protect the bark of saplings from frost cracking, to break the wind, and not to leave a heavy pruning wound open through the peak of the cold. Farin Kesht Taban tunes this list separately for apple, pear and almond orchards and for urban plane and ash, but the principles are shared.
Irrigation before hard frost
Dry soil transmits temperature swings to the roots and collar and drives the tree into winter physiological drought: an evergreen leaf turns brown, and a deciduous bud opens late or incompletely in spring. One deep autumn irrigation — when the air is cool but the soil has not yet frozen — fills the pore space with water and raises the soil's heat capacity. Do not confuse this with flooding at the foot of the trunk. The water must reach twenty to forty centimetres deep and have drainage. In orchards on an irrigation schedule, set the final round before a forecast frost. Once the surface has frozen, irrigation no longer infiltrates and only creates ice and suffocation. Evergreens, particularly pine and cypress, still transpire in winter wind; stored moisture is even more vital for them than for a fully dormant tree.
Whitewash on the trunks of saplings and young trees
On sunny winter days, the southern and western side of the trunk warms, and at night it suddenly freezes. The thin bark of an apple, peach, young plane and many pome fruit saplings cracks; this damage is called frost crack or winter sunscald. Diluted horticultural whitewash on the trunk reflects the radiation and reduces the temperature range. Building paint and toxic oil are not a substitute. Take the coating from the collar up to the first main branch, and in spring clean it off if the layer flakes. Wrapping hessian without ventilation in humid, snowy regions sometimes increases bark fungus; if you use a physical wrap, it must be removable and dry. Old trees with thick bark usually need no whitewash, except on a wounded or freshly pruned side.
Coordinate windbreaks and pruning with the cold spells
The dry winter wind of Khorasan and the open plains of Azerbaijan both empties the soil of moisture and breaks branches. A row of windbreak trees, a temporary matting on the prevailing wind side of the nursery, and even keeping the mulch over the root shade are all part of winterizing. Do not carry out heavy pruning at the peak of the cold, when the wood is frozen and brittle. A large wound in dry frost does not heal, and the surrounding cambium dies. In very cold regions, put formative pruning and the removal of thick branches off to late winter, close to bud swell. Removing a dead, hazardous branch for safety is the exception, and it must be a clean cut with the wound protected, on a day without frost.
- The last deep irrigation before the soil freezes, not flooding at the collar.
- Whitewash on the sun-facing side of the trunk for saplings and young trees.
- Mulch clear of the trunk to reduce freeze-thaw swings.
- A windbreak on the prevailing wind side; check the sapling stakes before the winter storms.
- Move the pruning of thick branches from very cold January to a milder March.
A trunk crack in February is not caused by February's cold; it comes from a bare trunk, dry soil and untimely autumn pruning.
Take a frost crack seriously, do not just paint over it
If you see a longitudinal crack on a trunk, do not fill it with cement or plaster. Keep the edge clean, reduce the moisture at the foot of the collar, and let the callus come gradually. Filling a cavity with building material drives the decay inwards. On an old urban tree, cracks and cavities are a matter of structural assessment, covered separately in the article on caring for veteran trees. Rodents gnaw the bark of saplings under snow; a mesh guard around the trunk is part of winterizing in the apple orchards of Hamadan and Khorasan. Cut out late nitrogen fertiliser so that soft tissue does not go into the frost.
- Check the soil moisture at spade depth and, if it is dry, give a pre-frost irrigation.
- Whitewash saplings in their first to third year and secure the stakes.
- Remove mounds of mulch and manure from the collar; spread a proper mulch layer with a gap.
- Move the heavy pruning programme out of the peak of the cold and remove only hazardous branches.
- After a frost event, record trunk cracks and evergreen scorch so that a corrective decision can be taken in March.
Shake heavy snow gently off young cypress and pine so the framework does not break; clear the snow from the collar of an old plane too, if it creates ice water at the foot of the trunk. Keep street salt away from the root shade of an urban tree; that same salt behaves like a saline fertiliser in spring. In the almond and apricot orchards of Hamadan, the flower buds wake early; your winterizing must protect bark and roots but must not wake the tree with late fertiliser. If you put a wrap on a trunk, take it off in early spring so it does not become a refuge for pests and moisture. Recording the orchard's minimum temperature with a simple thermometer advances the plan better than the rumour that this year is colder than last.
Winterizing a tree in Iran's cold belt has four pillars: water before the soil locks, protection of sapling bark against the winter sun, breaking the wind, and delaying heavy pruning. Draping plastic over the crown of a mature tree rarely substitutes for any of these, and usually creates scorch and fungus. If your orchard sits between two climates — the warmer edge of Khorasan, say, or the temperate slopes of the Zagros — set the intensity of each pillar by the minimum temperature of that particular district. Farkesht writes a winter visit before January so the task list is about the real tree rather than a national calendar. A heavy-cropping spring starts from a winter in which the tree did not crack and the roots did not dry.
