Frost damage to the olive tree - what to do if it does not expel?


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Olive tree - Olea europaea

All arrangements for hibernation go nowhere when an olive tree has to endure severe frosts below -10 degrees Celsius. There are mainly three types of frost damage that can cause an unexpectedly heavy winter on the Mediterranean fruit tree. Depending on whether roots, trunk and branches or the cambium are affected, you can save the noble tree with targeted measures. This green guide explains step-by-step what to do if an olea europaea stops working.

Hibernation in the garden - a climatic balancing act

Olive trees thrive and fruit only where winter temperatures approach the freezing point, at least for a short time. In tropical countries with permanently hot and humid-humid climates, you will therefore look in vain for olive plantations. In its habitats around the Mediterranean Sea, a true olive tree can stand up to - 10 degrees Celsius in dry winter climates. For hibernation in the German garden this requirement applies only conditionally. North of the Alps, the winter is characterized by long-lasting cold and plenty of wetness.
In addition, there are repeated changes between frost and thaw, which brings the Mediterranean Olea europaea to the edge of their capacity. Under these conditions, frost damage is not uncommon even within the Z8 winter hardiness zone, which actually allows hibernation in the open air. Particularly affected are young olive trees, as the frost tolerance builds up gradually until the temperature minimum of - 10 degrees Celsius.

Three types of frost damage

Olive gardeners and botanists distinguish the following 3 types of frost damage, which can be remedied with adequate measures:
  • Frost damage to the cambium
  • Frost cracks on the trunk and on the branches
  • Frostbite in the root area
The extent of these cold damages depends on various criteria, such as the local light and temperature conditions or the olive variety. Consequently, anchoring frost damage only at the minimum temperature is not enough. Other factors must be taken into account, such as the actual temperature profile, the temperature spread between plus and minus degrees or the actual duration of the frosty weather. Furthermore, the soil quality, the local light conditions and the constitution of the olive play an important role. In the following, we will explain in detail how to identify the actual frost damage and to motivate your True Olive tree to shoot again.

Frost damage to the cambium

The destruction of the cambium by frost is the biggest problem for olive trees in the garden. This applies equally to olives in the tub and the bed. The cambium is the growth layer between the outer bark and the physiologically active sapwood or xylem. This area contains the water and nutrient pathways. Thus, the cambium is primarily responsible for an important protective function. At the same time, it makes a contribution to the growth of trunk and instincts.
If your olive tree leaves its leaves hanging down after a bitterly cold winter's night or at worst drops it, a frozen cambium can be identified by two characteristics. The overlying bark can not be easily peeled off, because the frost has disturbed the metabolism so much that it is glued to the cambium.
Scrape off a little bit of bark, the first layer underneath is dark brown to black discolored. Unfortunately, the bark can still show an undamaged picture at this time, as it gradually develops an unhealthy brown discoloration as a chlorophyll-bearing layer. In case of suspicion, always take a look at the underlying cambium. This action plan fixes the problem:
  • Wait until mid / end of June with a pruning cut to recognize the new shoot
  • Perform a vitality test on all leafless branches by scraping the bark in places
  • Where no green tissue can be detected, a shoot has died
  • Use a sharp, clean pair of scissors to cut the twig into healthy, green wood
  • Completely dead branches on Astring auslichten

Olive tree - Olea europaea

If an olive tree with frost damage is radically cut back to healthy wood, it shows a different reaction than after a regular form and maintenance cut. As a rule, two opposing branches act below one interface. Not so with a frost-damaged copy. Here, the new drive shifts to the regions near the ground. This behavior thus allows a rebuilding of the crown, as he once succeeded with a parenting on the young olive tree.
Tip: After a comprehensive pruning due to frost damage, you can help the stressed olive tree with prudent care. Nitrogen-boosted fertilization and needs-based watering in a sunny, sunny location will boost growth again.

Frost cracks on trunk and branches

Frost cracks occur mostly in late winter. At this time, the temperatures at night still fall below freezing, while during the day the intensity of the sun's rays increases. As a result, the temperature fluctuations put the bark under tension. If this load gets overwhelming, the bark tears open lengthwise. Where this frost damage occurs, there is a need for immediate action. Should water penetrate the cracks and freeze, your olive tree will hardly recover from it. Diseases and pests use these wounds as a welcome attack surface. How to proceed professionally:
  • Wrap cracks of less than 5 cm in length with water-repellent, breathable fleece or straw band
  • Treat larger cracks in the cortex promptly with a wound closure agent, such as Malusan wound closure from Neudorff
  • Spread the preparation on the edge up to a maximum of 5 cm into the wound
  • Do not tear off loose pieces of bark, but fix them with small nails back to the trunk
The use of wound closure agents is discussed controversially among experts. The fact is that there is so far lack of scientific evidence that these funds prevent colonization of the tree with wood-destroying pathogens and pests. Nevertheless, the application after a frost crack is not useless. Wound closures have an effective protective function on the vital cambium. In this way they give the tree enough time to cover the wound. This is particularly true for frost damage, as they occur at a time when your olive tree is still in the dormancy. On the basis of this knowledge, we recommend that a rind in the bark is not applied over the entire surface but only with the agent along the edges of the wound.
Tip: Frost cracks on trees are also known as 'Labello effect'. Dryness not only ruptures lips in cold weather and sunlight. By watering your evergreen olive tree even in winter, you effectively prevent frost cracks.

Frostbite on the roots

Olive tree - Olea europaea

Frost damage in the root area affects primarily an olive tree in the tub. In its exposed position behind the vessel walls, a root ball is much more vulnerable to cold than in the shelter of the garden floor. In contrast to damage to the cambium or on the bark, frostbite on the roots are only apparent after the beginning of the growth and flowering period. Leaf loss and wilting flowers signal that supply via the roots is impaired. It is alarming if you can lift the olive tree with a light draft from the substrate. How to act correctly:
  • Pot the bale with the frost-damaged roots
  • Shake off the substrate completely for a clear view of the root system
  • Cut out dead, brown, rotten rhizomes
  • Pour the olive tree in fresh substrate and pour
Depending on the size of the root incision, it may be necessary to shorten the shoots proportionately. If half of the root volume falls away, a corresponding pruning of the branches by about 30 percent restores balance. A reduction of the root ball by a third or less can regulate your olive tree in the midst of the growing season itself. The gift of a plant fertilizer for Mediterranean woody plants has a beneficial effect on regeneration.
Conclusion
In Central European, wet and cold winters, an olive tree in the garden can cause significant damage even at temperatures around freezing. If the mercury column falls well below the temperature minimum of - 10 degrees Celsius, hardly any Olea europaea is spared. Frost damage occurs mainly on the cambium, trunk and branches as well as in the root area. So that the Mediterranean ornamental and fruit trees expel again, the package of measures should be based on the actual damaged area. A frost-damaged cambium requires a radical pruning down to healthy wood in early summer. Frost cracks, on the other hand, must be treated immediately in order to contain the damage. For larger wounds, special closures are recommended, while at smaller cracks already a water-repellent, breathable dressing is sufficient. If an olive tree in the tub suffers frostbite on the roots, the damage is remedied by a root incision, combined with repotting into fresh substrate.

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