When A Top Graft Fails

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Top-grafted shrubs, like this weeping Siberian pea shrub (Caragana arborescens ‘Walker’), are cute as a button… but not always long-lived.

Top-grafted shrubs, also called top-grafted standards or just standards, are shrubs grafted on top of the upright stem of a related species or variety. Often weeping or lollipoplike, with a rounded ball on top of a straight trunk, they’re very popular. They have a treelike appearance, yet barely grow in height, making them apparently ideal for today’s small lots. But they’re not always very long-lived.

A graft union – point where a grafted plant is attached to its rootstock – tends to be naturally weak. After all, it is a wound and wounds don’t always heal over perfectly. In fact, wounds in woody plants don’t actually heal at all, they compartmentalize, that is, new tissues grow over wounded tissue. That’s why a graft union always remains much more susceptible to weather damage, insects and disease than other parts of the plant.

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The graft union – where the top-graft is joined to the trunk – is the weakest part of the plant and often causes problems, especially on top-grafted shrubs.

When the graft union is at the foot of the plant, the way most fruit trees and ornamental conifers are produced, it is generally fairly well protected from the elements and tends to be strong, allowing the plant to live a near normal life. Top grafts, though, are very exposed to the elements, affected by wind, snow and ice buildup, freezing and thawing, etc. If a crack forms, rot or insects can work their way in or part of the top may simply snap off. That’s why so many top-grafted shrubs die after only few years.

But you can sometimes save a failing top-grafted shrub… if you know what to do.

A Spring Inspection

Often damage to top-grafted shrubs becomes most evident at winter’s end. Scarcely visible cracks may have spread or opened up under the influence of freezing and thawing or the weight of snow or ice on the branches. That’s why it’s always wise to examine your specimen each spring for signs of fissures or splitting.

If the top of the shrub does begin to split open, it’s often still possible to save it by essentially screwing it back together.

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Simply screw the splitting parts back together.

First, clean away any debris that may prevent the wound from closing. Then, drill two holes in the trunk, one on each side of the wound, one near the top of the crack, the other a few inches (5 to 10 cm) lower down. Countersink each hole, then insert a galvanized wood screw and tighten well to bring the two parts back together.

Apply no pruning paint, paste or any other so-called wound sealant. Such products tend keep the wound moist, whereas for the wound to cover over without inviting rot, it should be dry.

With a little luck, the wound will close as bark grows over it and should become pretty much invisible, although that will take likely a year or more.

Of course, sometimes this simply doesn’t work (if rot has set in, for example, the plant is pretty much a goner)… but at least you tried!

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