Modern findings on the effective treatment of wounds after pruning focus on the technical term "callus". Instead of sealing every cut with wax, prudent home gardeners leave this task to the self-healing powers of shrubs and trees. This guide gets to the heart of the function callus takes on in the regenerative process.

Callus are lumps that form around cuts

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  1. Callus - botanical definition with explanations
  2. This is how callus contributes to wound healing - the process in detail
  3. Wound closure torpedoes callus function

    4. Callus - botanical definition with explanations

    Bulbous growth of new tissue from undifferentiated cells at the edges of cuts and other injuries in woody plants. In the further course of the disease, there is extensive swelling of the wound from the outside inwards.

    It is characteristic of callus that the tissue forms directly from the thin ring of cambium that lies beneath the bark and bast, as illustrated in the figure below.

    Branch cross-section: 1 heartwood, 2 sapwood, 3 cambium, 4 bast, 5 bark.

    This is how callus contributes to wound healing - the process in detail

    Any injury on trees and shrubs puts the exposed cambium on alert. Fungal spores and pests lurk on every open wound on bushes and trees as an ideal target. Only rapid wound healing reduces the latent risk of infection. In order for healing to take place on its own, the cambium tissue undergoes a transformation process and becomes callus, which quickly overflows the wound. The following overview explains the individual phases of this exciting process:

    • First phase: callus formation in the form of irregularly shaped tissue cells as a small bulge along the edges of the wound
    • Second phase: Soft tissue forms bark tissue on the outside, wood tissue on the inside
    • Third phase: Fresh tissue overflows the wound from all sides

    Small cuts are overgrown with callus tissue within a short time. In the case of larger injuries, however, the process can drag on for many years. As soon as the edges of the wound meet in the center, the damaged tissue underneath is cut off from the air supply. Any fungi and pests that have already settled die off.

    The inward tissue cells close open vessels and form tannins. If rot and mold have already spread, these problem areas are separated from the rest of the tree by the tannin barrier.

    Wound closure torpedoes callus function

    We owe the father of modern arboriculture, Alex Shigo, the insight into how callus works. This goes hand in hand with the logical conclusion that any wound closure counteracts the self-healing process of woody plants. Since then, the use of impermeable sealants for treating wounds after pruning has been frowned upon - with one exception:

    If a wound is inflicted on the tree or shrub in the midst of winter, the exposed cambium should be protected from frost damage. To do this, smooth the injury with a knife. Then spread the edges of the wound thinly with tree wax (€12.96) to cover the valuable dividing tissue under the bark until next spring. This procedure is recommended for cuts with a diameter of 2 centimeters or more.

    tips

    Branches are always cut to astring so that the cambium can go through the transformation process into callus unhindered. The bulge between branch and trunk contains a high concentration of valuable cambium tissue and must therefore not be injured.

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