How Large A Cut Needs Sealant?

The instinct to seal a recent cut is reflexive. Selective application may speed up our work, however, and economize sealant.

In Bonsai Heresy I cover the arguments before and against cut sealants, on page 216. Although I cover the differences between bonsai and arborist techniques—and that both are right for their purposes—one thing I don’t touch on is cut size. The practical question is, “What cut is too small to bother with?”

Many conifer cuts, like pines and spruce, are not sealed at all. The resin is the sealant. Large wounds, such as the creation of shari on conifers, is an example where sealant is not used. 

Deciduous trees are another matter. These may experience dieback without a sealant, if the cut is a large one. Small cuts—1/32” to 1/8”—will die back to a bud no matter what you do, and sealing those is wasteful and pointless. Typically we should cut above the bud on these thin twigs, don’t seal, and let it die back to the bud you wish to push. 


A Styrax with two cuts. The cut to the right is 1/4” wide and received sealant. The cut above the bud is 1/16” wide and did not receive any. 

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  1. kiwijaz says:

    Michael, do you always cover the entire cut with sealant or could you just put a layer of sealant around the edge where the cambium layer is found?

    • crataegus says:

      Another good question…there are some diseases which appear to outrun the compartmentalizing process, which protects the plant from pathogens. Sort of like amputating a limb with gangrene—-sorry for the graphic example. But with large wounds on deciduous trees, some sort of sealant appears helpful. I like the latex sealants, but in Japan many use the putty sealants on deciduous.

  2. yenling29 says:

    I usually use sealant on small cuts for Ume only. My thought is that it could help reduce fungal issues. Do you think this is a waste or a good practice? Your blog is awesome!

    • crataegus says:

      Thanks for the question! It’s the central question I think…and my opinion is that in the very small shoot diameter, disease does not seem to enter. It may be because it dries out so fast, or the compartmentalization is swift, or such loss is so common that those areas are less susceptible—- but whatever the reason, I haven’t seen disease entering through the thin twigs. Plenty of problems with the larger cuts, though.

  3. mcole says:

    Thanks Michael. Very helpful

    Sent from my iPhone

  4. says:

    Good article Michael! What kind of cut paste is that you are using? It looks greenish and I like the match with the trees. Thanks, August

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