Experimenting with Calluses on Thuja Plicata Cuttings, Part I.
Towards the end of my experimental stage of working with Western Red Cedar (Thuja Plicata) cuttings, after I had gotten through the early days of failing with everything I stuck into the soil, I managed to get three particular old growth cuttings to retain their green foliage and appear to be on the brink of producing roots. They were originally planted on XXXXXX 2022, and pulled them out of the soil on January 7, 2023. So, they were in their original pot for XX months before I pulled them out, expecting to see a tangle of healthy roots…
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Second comment in the article… My work based experience with callusing of woody cuttings in general is that the callus blocks roots, with any roots present on cuttings with significant callusing appearing only where there were gaps in the callusing. So that the callus has to be trimmed, the cuttings re-stuck if there is to be any possibility of good rooting afterward.
I do not know of any Pinus strobus ever being grown from a cutting. Are you trying to root these or are you just doing a callous test? For the callous test you might try a conifer that is fairly easy to root. If you want to stay with pines, dwarf selections of Pinus mugo have several cultivars that root from summer cuttings. In my experience, cuttings that develop masses of callous tissue do not develop roots unless the tissue is removed and the cutting restuck. The callous tissue comes from the cambium, as doe the roots by differentiation. If the callous grows too fast it will prevent differentiation to roots by some of the cells. But roots will grow out through callous tissue if it is not too thick. Excessive rooting hormone will sometimes cause too much callous tissue to form.
literature (which I'm including well known garden blogs and university publications in that category) differs greatly on whether callusing is good or bad or a sign of progress or a sign of failure...houzz.com