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Protecting tree trunks

Sun scald in fruit and ornamental trees is on the rise

Protecting tree trunks

For more than 100 years, gardeners have practised the simple solution of painting ornamental and fruit trees white to protect them from sun damage. The world-renowned forestry and tree expert Dr. Alex L. Shigo (1930-2006) from the U.S. also repeatedly mentioned this problem in his presentations, and its occurrence in historic, gardening and forestry literature. The specialists know all about sun scalded bark. Garden lovers are only aware of the effects of this problem. Trunk protection should be standard practice not just for trees with thin bark, such as maples, horse chestnuts and lime trees, since tests show that all types of trees are susceptible to sun scald. Young tree trunks should be protected against the summer and winter sun for at least five years.

Handed-down gardening knowledge tells us that trees do not have to be protected against frost, but against heat. The problem is sunshine in the winter, combined with a dramatic change in temperature. As it's that time of year, in this article we are focusing on the approaching winter. It is worth noting, however, that this problem can also occur in summer due to strong overheating.

Sunburn necrosis in winter
Strongly fluctuating temperatures are responsible for frost cracks. The most critical situation is periods when part of the tree is above 0° C and the other part is below 0° C. In late winter, in particular, when temperatures above freezing cause the tree to start budding but then temperatures fall again dramatically, the tree can suffer sunburn necrosis. Frost then causes tears in the bark.

If you are planning to plant new trees, you must think about trunk protection in good time. At nurseries, some ornamental trees already have trunk protection. This is not standard practice for fruit trees, however. Here, tree owners are expected to sort themselves out, and protect the trunk by painting it white. This protective coating must cover the trunk right up to the lowest branches for approximately five to seven years after the tree was first planted. When choosing your paint, please note that different types have different life spans. As a rule, trunks must be repainted twice a year.

In Germany, a trunk protection paint with the trade name "Arbo-Flex" has been developed. This paint stays on the bark for five years. The slowly waning protective effect makes sure that the bark gradually adapts to the sun's rays at its site. Only apply trunk protection paint to a dry trunk on days without frost.

Trunk protection for old trees as well
Cutting and pruning often opens the way for branches of varying diameters. To protect these from the sun, white paint should also be applied here, to prevent damage in winter and summer.

Cracks that occur despite the application of white paint may be caused by the following:

  • Trees are very often placed in intermediate storage without protection before and after delivery.
  • Sometimes the trunk is only protected a while after the tree has been planted.
  • Fungal diseases

Conclusion
Every tree should be protected by white paint after planting, to prevent damage from the sun's rays. The trunk should be coated in white paint for at least five years. Paint should be applied to apricot and plum trees for a few years longer. Espalier trees, in particular, should have sun protection applied every year. Birch and plane trees are not painted at all.

Manfred Putz