I’ve created a post on Bonsainut.com in an effort to gather all information I possibly can from all corners of the interweb.
Here is a link to the thread itself, but below I’ll copy the discussion for the excessively lazy that won’t leave this forum (I know, I’m one of you too…)
It would honestly be helpful if you could keep it all in the bonsainut forum, but if not w/e.
"I’ve been trying to do research on this topic for awhile now, but I’ve never personally collected in the Late Summer/Fall. I have read stuff from Walter Pall, Harry Harrington (https://www.bonsai4me.com/AdvTech/ATquercus rootpruning and repotting.htm), and others about collecting at this time of year, and from my understanding I think Randy Knight collects from Spring constantly through Fall (different places for varying reasons such as a change in climate in collected area and where he houses them). I’ve read all over about this, but I’d love to get a solid discussion about this in one place rather than scattered all over different threads on different sites. I’m going to post information from everything I can find between Reddit, Mirai, BonsaiNut, etc. and then tag those involved in that discussion.
What I’d love to know more about from those who have collected is details . For deciduous, did you defoliate, did you leave leafs on, which species, where did you collect from, where do you live, how was the rootball when it came out, did you cutback root significantly or keep as many fine roots as possible, did you cutback the foliage to balance with roots, was it easily removed from its place in nature or was it a hard dig, yardadori or yamadori, aftercare that it was given, was it in a greenhouse, was it in full shade, did you mist or fertilize, did you place it on the ground if you potted it up (Randy Knight mentions this as paramount in survival), what medium was it planted in, etc. The list goes on, but the more information we can put together the better we can collectively understand the success of this technique of collecting outside of Spring (which is the more commonly practiced belief among most).
Also this video https://youtu.be/LxADFkspDQY was very informative. At the 11:45 marker Mauro Stemberger talks about a “resulgen area”? (I couldn’t understand what he was saying…) and he mentions that it has a somewhat better ability to push small roots and that it is common in Olives and Oaks. He says they almost collect no roots with the Oak he is talking about. He mentions that the cells of the wood are very active and that is part of the reason they re-root so well. This area is within the first 10-15cm from the base of the trunk.
Species that tend to like it from what I read (with tags with some of those who were successful): Larch, Ponderosa Pine, Tamarack, White Pine, Crape Myrtle, Hornbeam, Beech, Sweetgum (Late season to Summer), Linden @petegreg, European Hornbeam @petegreg, Scots Pine @petegreg, Norway Spruce @petegreg, Bald Cypress, Oaks, American Beech, American Hornbeam, Chinese Elm, Box Elder, Vine Maple @Arcto
Here are some interesting quotes I read while searching:
This is a 2 year old thread. However, Harry Harrington has a recent article in Bonsai Focus magazine about Autumn collecting. He says the success rate is higher, but you need to be able to protect the tree from frosts. In Autumn most trees are going into their biggest phase of root growth. Also, as temperatures go down the tree needs less water. When you collect in spring the tree has to grow new roots and put out foliage at the same time. Also, temperatures are rising and leaves are opening, so the tree starts to need more and more water soon after you’ve reduced its roots. It helps if the tree still has leaves when you collect in Autumn. This produces hormones that trigger root growth. Walter Pall and the book Modern Bonsai Practices also recommend collecting and repotting in Autumn. This idea is still new and controversial.
If you can’t provide frost protection, then collect in Spring.
Any tree that you can collect with sufficient foliage is best collected in late summer. The foliage will trigger hormones for root growth. The trees will soon go into their strongest phase of root growth and temperatures are getting cooler. In spring newly collected deciduous trees have to put out new leaves and grow new roots at the same time, which they may not have enough energy reserves for. Walter Pall recommended this in his recent maple repotting thread. I’ve had most success collecting many trees this time of year. Hornbeam, Elm, Beech, oak, etc. I like to keep the pots submerged in water for a couple of weeks if collecting at this time of year with foliage. Makes complete sense to me. This is only true if you can provide frost protection for collected trees.
No, I wouldn’t say collecting in spring and fall are equally advantageous. I have done both, but unless there’s a compelling reason I stick with a season of January 1 through March 31 for the bulk of the work. Sweetgum is collected after first flush, April through June works really well and better than in dormancy. You can lift Chinese elms after they come out, just defoliate. I’ve had worse luck with them in the dead of winter or prior to budding. Oaks can be collected later in the year, into summer, but not too late. Also defoliate (this is true for all deciduous when in leaf).
I’ve been told that the procedures are different for CA Live Oaks than for my FL Live Oaks…honestly the advice from adamaskwhy is all I can truly take as gospel, because I know he’s talking about the same specie in the same enviro!
I’d never had luck collecting an Oak til this past fall, when I collected one (on adam’s advice) because, after the rainy season, there’s optimal # fine/feeder roots under the trunk - I collected one that I’d trunk-chopped earlier in the year and it’s still alive now thankfully, though it’s a Laurel not Live (I really dig the deep grooving in Live Oak bark, gives a much more dramatic aged appearance!)
I agree on experimentation but jesus it’s tough putting in the time only for it to be a failure, right now I’m in the “collect a ton” mindset so, come spring / growing-time, I’ll at least have some that’ve made it!!
https://capebonsaikai.co.za/index.php?option=com_content&view=article&id=328:when-to-pot-what&catid=49:species-notes&Itemid=228 (Flip 6 months for Northern Hemisphere)