Causes of Freezing in Walnut Trees and Possible Protective Measures

         Late Frosts in Spring

o   After a temperature rise in March–April, walnut trees begin their vegetation period.

o   A sudden drop in temperature below 0°C can damage young buds, shoots, and blossoms.

o   Especially sensitive are the stages of bud break and young green shoots.

           Early Budding in Unstable Weather

o   Warm periods in February–March can trigger early sap flow.

o   Subsequent cold snaps can severely damage tissues due to their high water content.

           Insufficient Winter Hardiness

o   Walnut trees are warmth-loving plants.

o   Young trees (up to 3 years) are shallow-rooted, have thin bark and underdeveloped wood, making them more prone to freezing.

o   Temperatures below –20°C (especially without snow cover) are critical.

            Inappropriate Agronomic Practices

o   Late nitrogen fertilization in autumn promotes new growth that does not mature before winter.

o   Inadequate summer irrigation leads to weaker tissues that are more frost-sensitive.

o   Incorrect pruning in late autumn stimulates unwanted growth.

 Low-lying Locations and Cold Air Pockets

o   In plains and valleys, cold air lingers and can cause frost damage.

 

o   Seedlings in such areas are exposed to frost for longer periods.

 

 Selection of Suitable Varieties:

o   Choose frost-resistant varieties like:

§  Chandler

§  Fernette

§  Fernor

§  Franquette

§  Lara

§  Tulare

§  Ronde de Montignac

 Proper Planting Location

o   Avoid low-lying areas where cold air accumulates (frost pockets).

o   Choose sunny, south or southwest-facing slopes where snow melts quickly and air circulates better.

o   Protect from north and east winds using hedges, windbreak nets, or buildings.

Adjustment of Agronomic Practices

 Irrigation:

·        Ensure moderate but regular irrigation during the growing season.

·        Reduce irrigation toward the end of summer to harden plant tissues.

Fertilization:

For Conventional Growers:

·        Spring (March–April): Nitrogen fertilizer – 30–50 kg/ha in two doses:

o   First dose – early spring

o   Second dose – early June

·        Micronutrients (boron, zinc, magnesium): Foliar feeding, 1–2 sprays in May–June.

·        Summer (June): Stop nitrogen fertilization after mid-June to avoid soft growth.

·        Autumn (Sept–Oct): Compound NPK fertilizer high in potassium and phosphorus; organic fertilizer optionally every 2–3 years.

For Organic Growers:

·        Spring: Compost or well-rotted manure (300–500 kg/ha), depending on soil fertility; plant extracts (nettle, legumes) as liquid fertilizers 2–3 times per season; foliar feeding with organic-certified boron and zinc products.

·        Summer: Balanced fertilization with plant extracts; stop fertilization by late June.

·        Autumn: Wood ash as a potassium source (50–100 kg/ha) – apply carefully due to pH; potassium-rich compost; mulching with straw or leaves – retains heat and moisture, protects against frost.

 Pruning:

·        Avoid late autumn pruning – it promotes immature growth.

·        Recommended time: late winter or early spring before bud break.

Physical Protection of Seedlings in Winter

o   Mulch the root zone (thick layer of straw, leaves, manure) – helps retain soil heat and moisture.

Planting at Correct Depth

o   When planting in autumn or spring, the root collar should be about 4–5 cm below the soil surface.

o   This protects the seedling base from frost.

Adaptation to Local Climate

 

o   In very cold regions, spring planting is preferable when the risk of frost is lower.

Restoring frost-damaged walnut seedlings requires attention, patience, and proper care.

Diagnosing Demage

o   Buds: blackened, dry, or fallen.

o   Bark: grayish-brown, cracked or peeling.

o   Shoots: darkened, soft, or shriveled.

o   Trunk: if a scratch under the bark shows brown tissue, it is dead.

o   Roots: damaged roots may indicate seedling death; healthy roots are white/yellowish and juicy when cut.

Pruning Frost-Damaged Parts

When:

·        Early spring, once the risk of further frost is gone.

How:

·        Cut down to healthy tissue where the inner bark is green.

·        Use a sharp, disinfected pruner.

Post-Frost Irrigation and Care

·        Provide regular, moderate watering, especially during dry periods.

·        Avoid overwatering – can lead to root rot.

·        Mulch with organic materials – maintains moisture and improves root zone microclimate.

Additional Care for Recovery

·        Support: Use a stake to stabilize weakened seedlings.

·        Pest Protection: Frost-damaged plants are more vulnerable to diseases and insects.

·        Weed Control: Prevent competition for water and nutrients.

When Is Recovery Impossible?

·        If the main trunk and root collar are completely frozen and dry.

·        If no healthy buds remain on the trunk.

 

·        If the bark is completely detached (e.g., due to sunscald + frost).