Sciencing the Juniperus Communis yamadori riddle?

Hi everyone,
I’m new to the forum, and fairly new to bonsai. I’ll try to be as succinct as possible:

I live in sweden, and I’ve been thinking about what I can collect. Sadly, we only have one native juniper species - Juniperus Communis. I’ve come to understand that JC has a very poor reputation as yamadori, but no one seems to know why. I’ve read lots and lots by bonsai professionals and even quite a few scientific articles by now, and the only possible reason I’ve found is the growth habit of the roots (mainly in the top 10-15 cm of the soil, widely spreading).

Is this not a ridiculous state of affairs? Should we not be able to science this and find a somewhat high-success collection, aftercare and care routine?

I want to do this. However, the hive mind is always smarter than any single person. My suggestion is that we figure this out. Reading, reaching out to people in the professional and scientific communities, and of course testing hypotheses. Anyone interested?

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Hi Gustav,
I’m interested in Juniperus Communis for the same reason as you (living in Serbia communis is native plant). I collected one this spring and it’s doing well for now. Can you upload articles to forum ?
In Serbia communis grow vertical without deadwood, it is hard to find some interesting yamadry maybe it is main problem.

I’m guessing that the US variety is actually quite different than the European variety despite having a similar appearance, however, I can tell you with my experience here that they don’t like Akadama. A few years ago I took some rooted cuttings, put one in potting soil, one in pumice and one in Akadama. The Akadama one survived but was very weak and had almost no new roots while the potting soil and pumice cuttings thrived.

When collecting, you absolutely have to get a nice root pad or it’s death. Here they often grow on talus where the roots go quite a long ways before developing feeder roots and are impossible to collect. Sometimes, even with a nice root pad, they never perk up and just randomly die. I have to keep them out of direct sun for quite a while, sometimes even for 6 to 8 months. My fall collected ones go on a heat pad and are eased into direct sun around late May. I keep a close eye on them and any signs of desiccation they go back into shade. Heat pad will help roots grow through winter but won’t save a tree without a nice root pad. I have a couple that stayed alive but took two years to start pushing new growth. They die slooooowly. I’ve collected 11, all with nice roots and four of them never perked up and eventually died.

Cedar apple rust is a huge problem completely and obliterated one of my nicer trees. Leaving the bark on the live veins seems to help. I spray with mancozeb when the apple/pears nearby have fruiting bodies and make sure to really soak the live veins. When I had an outbreak two years ago, I completely defoliated the apple trees on my property to avoid them being infected and continuing the cycle.

Here is how the roots look on a fall collected tree that spent the winter in the shade on a heat bed:

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I should also mention that the variety here ground layers very easily. They often grow foliage in a big clump where new branches are always sprouting from the same area and form a sortof burl. Those burls will produce new roots just as easily as new foliage, so you can hedge your bets by putting pumice under those clumps when you collect.

As I understand it, collected Sabina juniper go through some sort of root cleaning process post collection, though not immediately it seems. I think its to remove some sort of pathogen that will overwhelm the plant in a pot but not necessarily where it grows. Perhaps Communis experiences the same or a similar phenomenon?

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Thank you very much for your answers!

I’ve read that other places as well, which makes it a pattern. Quite interesting. Potting soil would be wetter than akadama, and pumice dryer (right?), so excessive moisture retention can’t be the problem there. I believe I’ve read something about young JCs not wanting high nitrogen, so maybe that is something to consider?

What sort of time frame are we talking about? Do they sort of gradually fade, or does a lot of time pass, and then they die?

Same here. I’ll have to check how big the genetic diversity is across JC. I’ve found some data pertaining to JC in the british isles, and if that is any indication, the variability is pretty big. This seems to indicate the same for Europe.

Maybe! The root pathogen angle is something I need to look at. You wouldn’t happen to know what affects sabina?

I found this site a good read: Biological Flora of the British Isles: Juniperus communis L.

And, among a few other parts, this:

Juniper appears to be tolerant of all but the severest drought. [Gilbert (1980] noted a number of possible reasons for poor juniper regeneration in Teesdale but included the exceptional drought of 1976. On the thin limestone soils of the Alvar grasslands of Sweden, [Rosén (1995] found that mortality was highly synchronized with severe drought and [García et al . (1999b] suggested that drought was the most probable cause of ageing populations found in Mediterranean mountain juniper populations. By contrast, juniper is intolerant of flooding ([Glenz et al . 2006] On three sites of contrasting soil water content ([Hill et al . 1996], it was found that the sex ratio of female to male trees was around 1 : 1 on the drier sites but 11 : 1 on the waterlogged site, suggesting that male trees are less tolerant of waterlogging. Foliar carbon discrimination (δ13C) was more negative for both sexes on the waterlogged site.

I found this very interesting. Does anyone know if any bonsai people have looked into the differing needs/vulnerabilities of female and male junipers?

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Before I realized the thing about Akadama, I had one tree that I let recover using the technique Dan Robinson uses where you just leave the rootball in the bag it was collected in, cut some drainage holes and put it on the ground for a season. The next season I put it in a 1:1:1 Akadama/Pumice/Lava mix and it seems to be doing fine. This makes me think it still has something to do with the moisture retention, as an established rootball is able to pull moisture from the container faster than a rooted cutting placed in pure Akadama. I won’t know for sure until I can inspect the roots the next time I repot. Not sure why they don’t seem to mind potting soil.

After you collect them, they never start pushing new growth from the tips and slowly decline over the next 6-8 months. It starts with die back on the interior but eventually the tips start to look desiccated and turn brown.

Looking at the scientific literature I’ve read, the only thing (wild) JC seem to really hate is waterlogged soil and really dense clay. I really should see what the growth rate of JC roots is like compared to other junipers. Maybe that is a thing.

To me, that sounds more like some inability to “get going” again post collection (tree attempts to shed some foliage to regain “balance”, like) more than some kind of pathogen or shock (with shock I mean an environmental one, like maybe shifting the pH of the soil too quickly or whatever), but that is a guess. What’s your intuition?

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I really have no idea. The ones I had that died came from the same location as others that thrived, had nice root pads and went into the same heat bed in the same pumice. There may be differences in the cultivars, for example, in one of my favorite locations for collecting lodgepole pines, you occasionally find a variety that has extremely short needles (like less than a cm) and very gnarly branch formation. They never ever survive transplantation while other cultivars from the same area do fine.

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I wonder if the Akadama problem is due to the PH of the soil. Many junipers tend to like alkaline. In the Puget Sound, we have a Maritime Juniper that I’ve been propagating from cuttings and it is often found in places right on the shore and bluffs that were once beaches and/or contained midden piles, which are very basic. I use crushed seashells in the soil for these and they do great. JC here almost exclusively grow on basalt which is also fairly basic. If the JC’s in Europe are typically found on limestone, that could be the issue.

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When collecting or lifting any juniper that’s lived in the same place for a number of years it is always wise to undercut about 12 months before lifting. This is usually done in May as that’s normally the time when they are in full swing. This forces feeder roots to grow closer to the trunk. When lifting a tree I like to take as much of the ground soil as I can and pot it up in a compost / grit mixture. This is where the microbial activity is and it helps it to settle into pot life rather than shocking it too much with completely different soil. I will then wait, if it has grown a significant amount I will repot the following year into 1.1.1. but if not I’ll wait for a further 12 months. Akadama stays too wet for a freshly lifted tree and actually drowns it. There are a couple of videos on how to pot up a yamadori using pumice, one with Randy Knight, the famous collector, however these trees aren’t communis and are lifted in the mountains where it is impossible to undercut.

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From what I gather, they tolerate a ton of different pH, and absolutely the slightly acidic/neutral of akadama. But the change from one to the other is less clear.

From a bit of reading: JC seems to have relationships with a ton of fungi, but it seems to be a facultative ectromycorrhizal rather than an obligate one, so getting fungi should not be as important as with e.g. pines. Maybe the bacterial environment matters? Or indeed just the change. Thanks! What would you say your success rate is with your current method?

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I forgot to mention that prior to lifting the juniper should not be pruned as that’s where they get their energy

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This is a sabina juniper that I lifted in May. It was undercut last may. I also made sure that plenty of soil remained with it when potting up although I did take off quite a bit.
It is about 45yrs old. It was dug up and given to me about 15 yrs ago where I planted it in my garden. 12yrs ago it was dug up and planted in the garden at my new house where until last year no root work had been done. It had a couple of light prunings during this time. Other than a bit of conifer scale, it is doing well and has put on quite a bit of growth.
Watering has to be carefully monitored as the soil tends to dry out faster than thee compost. Tricky but manageable.
I have a blauws juniper that has been in the ground for 20 years and in that time it has been in 4 different locations (we move around a bit!!), with no ill effects.

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That is a cool peice of material for sure. However, I feel like the moving of sabina junipers, and most definitely blauws (eg chinensis) is well understood compared to Communis, so I’m not sure if the methods necessarily translate. The Communis seems to be its own animal.

But the principle would be the same. Leave the foliage, undercut 12 months prior, check there is sufficient rootball and pot into a suitable container which it just fits into and has lots of air holes, at least at the bottom.

Have you done it reliably with communis? Don’t get me wrong, it sounds perfectly reasonable and I would probably do something similar if I were to try it today. Most people just seem oddly agreed on JC being not like the others, and I’m hoping to find where the stumbling block is.

Hi Gustav, I don’t actually like communis. There’s just something that resonates with me about them. If I was to lift one from the wild I would definitely use my method. There are obviously more details to look at though. Such as the environment it is currently in and how to replicate this in the short term. What aftercare would be required such as morning sun as a minimum etc.
You may even want to take two years to lift and start by undercutting at 1 metre the first year
then go back the following year and do 60cm and lift in the third year.
Not over potting would also be crucial so the tree doesn’t drown.
However you do it, the basic method remains the same.
One alternative would be to undercut as normal then lift the following year but instead of potting up plant in your garden for a year or two. Or try sawdust as Randy Knight recommends.

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Cheers Keith, I appreciate the input.

For anyone interested, here are a few pertinent bits I’ve been able to find:

  • In a study over several decades, the authors of one study wrote the following: " From approximately 24 to 47 years, there was a slow but steady decrease in the proportion of females, and the sex ratio could be predicted by bush age.[A bit about rabbit damage] Of the damaged individuals that died later, more were females and all were in poor condition succumbing eventually with severe basal and root cankers and rots. Stressed females may have been more vulnerable to these pathogens, which caused loss of rooting, and probably consequently caused water stress on the dry chalk soils." (Which makes me think there might be something to female JCs being a bit less tolerant of disturbance)

  • As for pathogens, it seems JC get “Tip blight” (Phomopsis), “Root rots” (Phytophtora) and “Leaf and shoot death” (Coniothyrium fuckelii Sacc.) and others. Phytophtora of different types seem occasionally wipe out whole populations.

The quote above - to me - suggests the hypothesis is that the collection process might give one or several root/soil pathogens a boost, making the tree less tolerant of suboptimal watering. It might be that a collected JC often ends up walking a tight rope between too wet (risking rot, too little oxygen, and hence further root degeneration) or underwatered, with nothing to spare.

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I wouldn’t be surprised if there are differences here too between males and females. Here the males are usually not great trees for bonsai. They tend to have very leggy/extending foliage while the females are more mounded and compact. So even if males are more tolerant of adverse conditions, they usually aren’t worth collecting.

For example, here is a very large male. This is the same tree as in the heat bed root photo I posted above. The foliage is mostly at the end of very long tentacle like branches that keep extending every year. Making it compact is going to be difficult…I will probably opt to graft in some foliage at better locations next year.

These are both females (they had seed when they were collected three years ago):

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Hi Gustav, have you thought about grafting on roots from a domestic variety of communis? Possibly 2 or 3 plants round the base of the trunk may eliminate the problems of lifting from the wild. Once they’ve fused together you should be able to lift and settle into a pot. Then a couple of years later remove the foliage from the grafted ones. Just an idea…

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