Grafting compound is a thick sealant applied to a fresh graft union to limit desiccation while the graft knits. A bit more typically gets applied to the cut distal end of the scion. There are various formulations of grafting compound, ranging from something resembling roof patch to a something with the consistency of thick paint.
The stuff, as sloppy and icky as it is, really is helpful. I can not imagine how big orchards were grafted before it was invented.
It is also useful for keeping cane borers out of the cut ends of freshly pruned roses. For those of us who remember how to prune roses properly, leaving only a few thick canes, grafting compound really is practical. I just don’t use it on roses because cane borers are not a problem here.
Since I do not use grafting compound on roses, and the plants that I graft do not need grafting compound, I presently have no use for it. I suppose I could use it on apple and pear trees, but it really is not necessary. When I get around to grafting apricots and peaches, it will only be for a few trees in my own garden, so I will just use candle wax.
This surprises people. At work, I am often asked about ‘painting’ pruning wounds and shiners as trees get pruned, presumably with sealant. Decades ago, it was actually commonly done. Even when I did my internship in arboriculture in 1988, some arborists were applying sealant because it was easier than arguing with their clients about it not being necessary.
The problem with applying sealant to large wounds is that is actually seals moisture within the otherwise exposed wood, and promotes rot. It is best to do nothing, and allow the affected trees to compartmentalize their wounds as they would do naturally if limbs were broken off by the weather. Trees know more about their processes than we do.
Tony Tomeo 
I had a Sweetgum heal a big hole in its trunk. It was drippy wet all the time and I guess it was healing itself.
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If it was dripping constantly, the wood within was likely rotting to some degree. It is normal, but some trees expel associated fluids more than others do, especially if the decaying tissue is compressed by healthy growth around it. Sealing such wounds actually enhances such decay without stopping the bleeding. Sweetgum is also susceptible to slime flux, which typically infects healthy tissue without a wound, but sometimes infects just within the callus roll (vascularly active tissue of accelerated growth intended to compartmentalize a wound). Sealants interfere with the draining of fluids, which promotes decay.
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It seems OK. I had an arborist (I think he was trained) look at it and said I didn’t need to cut it down. Hopefully it will be alright as it is on the property line.
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Such oozing is not as bad as it looks, and slime flux is generally harmless. It just smells objectionable and looks unsightly. There is no remedy for slime flux.
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When I prune roses I should leave only a few thick canes? I was taught I could leave anything thicker than a pencil that was otherwise positioned right and not dead or diseased.
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Yes, that is accurate. I leave about five. More can be left for vigorous plants. Old canes that were left to bloom last year should be removed. Fat canes that grew this year should be retained. It is sometimes necessary to retain canes that are not in the best positions if they are the only options. It might also be necessary to retain old canes if there are not enough new canes. I sometimes cut out the old canes even if it leaves less than five, because removing old growth stimulates generation of new growth.
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Reblogged this on Tony Tomeo and commented:
Actually, it seems to me that the unnecessary use of sealant on shiners has become less common during the past three years since this recycled article was posted.
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